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-rw-r--r--html/065duplex_list.mu.html1124
1 files changed, 574 insertions, 550 deletions
diff --git a/html/065duplex_list.mu.html b/html/065duplex_list.mu.html
index ce239cde..d21807e2 100644
--- a/html/065duplex_list.mu.html
+++ b/html/065duplex_list.mu.html
@@ -6,7 +6,7 @@
 <meta name="Generator" content="Vim/7.4">
 <meta name="plugin-version" content="vim7.4_v2">
 <meta name="syntax" content="none">
-<meta name="settings" content="use_css,pre_wrap,no_foldcolumn,expand_tabs,prevent_copy=">
+<meta name="settings" content="number_lines,use_css,pre_wrap,no_foldcolumn,expand_tabs,line_ids,prevent_copy=">
 <meta name="colorscheme" content="minimal">
 <style type="text/css">
 <!--
@@ -15,10 +15,11 @@ body { font-size: 12pt; font-family: monospace; color: #eeeeee; background-color
 * { font-size: 12pt; font-size: 1em; }
 .muData { color: #ffff00; }
 .muControl { color: #c0a020; }
+.Special { color: #c00000; }
 .Delimiter { color: #800080; }
 .Comment { color: #9090ff; }
 .Constant { color: #00a0a0; }
-.Special { color: #c00000; }
+.LineNr { color: #444444; }
 .muRecipe { color: #ff8700; }
 .muScenario { color: #00af00; }
 -->
@@ -27,558 +28,581 @@ body { font-size: 12pt; font-family: monospace; color: #eeeeee; background-color
 <script type='text/javascript'>
 <!--
 
+/* function to open any folds containing a jumped-to line before jumping to it */
+function JumpToLine()
+{
+  var lineNum;
+  lineNum = window.location.hash;
+  lineNum = lineNum.substr(1); /* strip off '#' */
+
+  if (lineNum.indexOf('L') == -1) {
+    lineNum = 'L'+lineNum;
+  }
+  lineElem = document.getElementById(lineNum);
+  /* Always jump to new location even if the line was hidden inside a fold, or
+   * we corrected the raw number to a line ID.
+   */
+  if (lineElem) {
+    lineElem.scrollIntoView(true);
+  }
+  return true;
+}
+if ('onhashchange' in window) {
+  window.onhashchange = JumpToLine;
+}
+
 -->
 </script>
 </head>
-<body>
+<body onload='JumpToLine();'>
 <pre id='vimCodeElement'>
-<span class="Comment"># A doubly linked list permits bidirectional traversal.</span>
-
-<span class="muData">container</span> duplex-list:_elem [
-  value:_elem
-  next:&amp;:duplex-list:_elem
-  prev:&amp;:duplex-list:_elem
-]
-
-<span class="Comment"># should I say in/contained-in:result, allow ingredients to refer to products?</span>
-<span class="muRecipe">def</span> push x:_elem, in:&amp;:duplex-list:_elem<span class="muRecipe"> -&gt; </span>in:&amp;:duplex-list:_elem [
-  <span class="Constant">local-scope</span>
-  <span class="Constant">load-ingredients</span>
-  result:&amp;:duplex-list:_elem <span class="Special">&lt;-</span> new <span class="Delimiter">{</span>(duplex-list _elem): type<span class="Delimiter">}</span>
-  *result <span class="Special">&lt;-</span> merge x, in,<span class="Constant"> 0</span>
-  <span class="Delimiter">{</span>
-    <span class="muControl">break-unless</span> in
-    *in <span class="Special">&lt;-</span> put *in, <span class="Constant">prev:offset</span>, result
-  <span class="Delimiter">}</span>
-  <span class="muControl">return</span> result  <span class="Comment"># needed explicitly because we need to replace 'in' with 'result'</span>
-]
-
-<span class="muRecipe">def</span> first in:&amp;:duplex-list:_elem<span class="muRecipe"> -&gt; </span>result:_elem [
-  <span class="Constant">local-scope</span>
-  <span class="Constant">load-ingredients</span>
-  <span class="muControl">return-unless</span> in,<span class="Constant"> 0</span>
-  result <span class="Special">&lt;-</span> get *in, <span class="Constant">value:offset</span>
-]
-
-<span class="muRecipe">def</span> next in:&amp;:duplex-list:_elem<span class="muRecipe"> -&gt; </span>result:&amp;:duplex-list:_elem/contained-in:in [
-  <span class="Constant">local-scope</span>
-  <span class="Constant">load-ingredients</span>
-  <span class="muControl">return-unless</span> in,<span class="Constant"> 0</span>
-  result <span class="Special">&lt;-</span> get *in, <span class="Constant">next:offset</span>
-]
-
-<span class="muRecipe">def</span> prev in:&amp;:duplex-list:_elem<span class="muRecipe"> -&gt; </span>result:&amp;:duplex-list:_elem/contained-in:in [
-  <span class="Constant">local-scope</span>
-  <span class="Constant">load-ingredients</span>
-  <span class="muControl">return-unless</span> in,<span class="Constant"> 0</span>
-  result <span class="Special">&lt;-</span> get *in, <span class="Constant">prev:offset</span>
-  <span class="muControl">return</span> result
-]
-
-<span class="muScenario">scenario</span> duplex-list-handling [
-  run [
-    <span class="Constant">local-scope</span>
-    <span class="Comment"># reserve locations 0-9 to check for missing null check</span>
-    10:num/<span class="Special">raw</span> <span class="Special">&lt;-</span> copy<span class="Constant"> 34</span>
-    11:num/<span class="Special">raw</span> <span class="Special">&lt;-</span> copy<span class="Constant"> 35</span>
-    list:&amp;:duplex-list:char <span class="Special">&lt;-</span> push<span class="Constant"> 3</span>,<span class="Constant"> 0</span>
-    list <span class="Special">&lt;-</span> push<span class="Constant"> 4</span>, list
-    list <span class="Special">&lt;-</span> push<span class="Constant"> 5</span>, list
-    list2:&amp;:duplex-list:char <span class="Special">&lt;-</span> copy list
-    20:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> first list2
-    list2 <span class="Special">&lt;-</span> next list2
-    21:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> first list2
-    list2 <span class="Special">&lt;-</span> next list2
-    22:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> first list2
-    30:&amp;:duplex-list:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> next list2
-    31:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> first 30:&amp;:duplex-list:char/<span class="Special">raw</span>
-    32:&amp;:duplex-list:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> next 30:&amp;:duplex-list:char/<span class="Special">raw</span>
-    33:&amp;:duplex-list:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> prev 30:&amp;:duplex-list:char/<span class="Special">raw</span>
-    list2 <span class="Special">&lt;-</span> prev list2
-    40:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> first list2
-    list2 <span class="Special">&lt;-</span> prev list2
-    41:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> first list2
-    50:bool/<span class="Special">raw</span> <span class="Special">&lt;-</span> equal list, list2
-  ]
-  memory-should-contain [
-   <span class="Constant"> 0</span> <span class="Special">&lt;-</span><span class="Constant"> 0</span>  <span class="Comment"># no modifications to null pointers</span>
-   <span class="Constant"> 10</span> <span class="Special">&lt;-</span><span class="Constant"> 34</span>
-   <span class="Constant"> 11</span> <span class="Special">&lt;-</span><span class="Constant"> 35</span>
-   <span class="Constant"> 20</span> <span class="Special">&lt;-</span><span class="Constant"> 5</span>  <span class="Comment"># scanning next</span>
-   <span class="Constant"> 21</span> <span class="Special">&lt;-</span><span class="Constant"> 4</span>
-   <span class="Constant"> 22</span> <span class="Special">&lt;-</span><span class="Constant"> 3</span>
-   <span class="Constant"> 30</span> <span class="Special">&lt;-</span><span class="Constant"> 0</span>  <span class="Comment"># null</span>
-   <span class="Constant"> 31</span> <span class="Special">&lt;-</span><span class="Constant"> 0</span>  <span class="Comment"># first of null</span>
-   <span class="Constant"> 32</span> <span class="Special">&lt;-</span><span class="Constant"> 0</span>  <span class="Comment"># next of null</span>
-   <span class="Constant"> 33</span> <span class="Special">&lt;-</span><span class="Constant"> 0</span>  <span class="Comment"># prev of null</span>
-   <span class="Constant"> 40</span> <span class="Special">&lt;-</span><span class="Constant"> 4</span>  <span class="Comment"># then start scanning prev</span>
-   <span class="Constant"> 41</span> <span class="Special">&lt;-</span><span class="Constant"> 5</span>
-   <span class="Constant"> 50</span> <span class="Special">&lt;-</span><span class="Constant"> 1</span>  <span class="Comment"># list back at start</span>
-  ]
-]
-
-<span class="Comment"># insert 'x' after 'in'</span>
-<span class="muRecipe">def</span> insert x:_elem, in:&amp;:duplex-list:_elem<span class="muRecipe"> -&gt; </span>in:&amp;:duplex-list:_elem [
-  <span class="Constant">local-scope</span>
-  <span class="Constant">load-ingredients</span>
-  new-node:&amp;:duplex-list:_elem <span class="Special">&lt;-</span> new <span class="Delimiter">{</span>(duplex-list _elem): type<span class="Delimiter">}</span>
-  *new-node <span class="Special">&lt;-</span> put *new-node, <span class="Constant">value:offset</span>, x
-  <span class="Comment"># save old next before changing it</span>
-  next-node:&amp;:duplex-list:_elem <span class="Special">&lt;-</span> get *in, <span class="Constant">next:offset</span>
-  *in <span class="Special">&lt;-</span> put *in, <span class="Constant">next:offset</span>, new-node
-  *new-node <span class="Special">&lt;-</span> put *new-node, <span class="Constant">prev:offset</span>, in
-  *new-node <span class="Special">&lt;-</span> put *new-node, <span class="Constant">next:offset</span>, next-node
-  <span class="muControl">return-unless</span> next-node
-  *next-node <span class="Special">&lt;-</span> put *next-node, <span class="Constant">prev:offset</span>, new-node
-]
-
-<span class="muScenario">scenario</span> inserting-into-duplex-list [
-  <span class="Constant">local-scope</span>
-  list:&amp;:duplex-list:char <span class="Special">&lt;-</span> push<span class="Constant"> 3</span>,<span class="Constant"> 0</span>
-  list <span class="Special">&lt;-</span> push<span class="Constant"> 4</span>, list
-  list <span class="Special">&lt;-</span> push<span class="Constant"> 5</span>, list
-  run [
-    list2:&amp;:duplex-list:char <span class="Special">&lt;-</span> next list  <span class="Comment"># inside list</span>
-    list2 <span class="Special">&lt;-</span> insert<span class="Constant"> 6</span>, list2
-    <span class="Comment"># check structure like before</span>
-    list2 <span class="Special">&lt;-</span> copy list
-    10:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> first list2
-    list2 <span class="Special">&lt;-</span> next list2
-    11:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> first list2
-    list2 <span class="Special">&lt;-</span> next list2
-    12:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> first list2
-    list2 <span class="Special">&lt;-</span> next list2
-    13:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> first list2
-    list2 <span class="Special">&lt;-</span> prev list2
-    20:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> first list2
-    list2 <span class="Special">&lt;-</span> prev list2
-    21:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> first list2
-    list2 <span class="Special">&lt;-</span> prev list2
-    22:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> first list2
-    30:bool/<span class="Special">raw</span> <span class="Special">&lt;-</span> equal list, list2
-  ]
-  memory-should-contain [
-   <span class="Constant"> 10</span> <span class="Special">&lt;-</span><span class="Constant"> 5</span>  <span class="Comment"># scanning next</span>
-   <span class="Constant"> 11</span> <span class="Special">&lt;-</span><span class="Constant"> 4</span>
-   <span class="Constant"> 12</span> <span class="Special">&lt;-</span><span class="Constant"> 6</span>  <span class="Comment"># inserted element</span>
-   <span class="Constant"> 13</span> <span class="Special">&lt;-</span><span class="Constant"> 3</span>
-   <span class="Constant"> 20</span> <span class="Special">&lt;-</span><span class="Constant"> 6</span>  <span class="Comment"># then prev</span>
-   <span class="Constant"> 21</span> <span class="Special">&lt;-</span><span class="Constant"> 4</span>
-   <span class="Constant"> 22</span> <span class="Special">&lt;-</span><span class="Constant"> 5</span>
-   <span class="Constant"> 30</span> <span class="Special">&lt;-</span><span class="Constant"> 1</span>  <span class="Comment"># list back at start</span>
-  ]
-]
-
-<span class="muScenario">scenario</span> inserting-at-end-of-duplex-list [
-  <span class="Constant">local-scope</span>
-  list:&amp;:duplex-list:char <span class="Special">&lt;-</span> push<span class="Constant"> 3</span>,<span class="Constant"> 0</span>
-  list <span class="Special">&lt;-</span> push<span class="Constant"> 4</span>, list
-  list <span class="Special">&lt;-</span> push<span class="Constant"> 5</span>, list
-  run [
-    list2:&amp;:duplex-list:char <span class="Special">&lt;-</span> next list  <span class="Comment"># inside list</span>
-    list2 <span class="Special">&lt;-</span> next list2  <span class="Comment"># now at end of list</span>
-    list2 <span class="Special">&lt;-</span> insert<span class="Constant"> 6</span>, list2
-    <span class="Comment"># check structure like before</span>
-    list2 <span class="Special">&lt;-</span> copy list
-    10:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> first list2
-    list2 <span class="Special">&lt;-</span> next list2
-    11:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> first list2
-    list2 <span class="Special">&lt;-</span> next list2
-    12:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> first list2
-    list2 <span class="Special">&lt;-</span> next list2
-    13:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> first list2
-    list2 <span class="Special">&lt;-</span> prev list2
-    20:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> first list2
-    list2 <span class="Special">&lt;-</span> prev list2
-    21:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> first list2
-    list2 <span class="Special">&lt;-</span> prev list2
-    22:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> first list2
-    30:bool/<span class="Special">raw</span> <span class="Special">&lt;-</span> equal list, list2
-  ]
-  memory-should-contain [
-   <span class="Constant"> 10</span> <span class="Special">&lt;-</span><span class="Constant"> 5</span>  <span class="Comment"># scanning next</span>
-   <span class="Constant"> 11</span> <span class="Special">&lt;-</span><span class="Constant"> 4</span>
-   <span class="Constant"> 12</span> <span class="Special">&lt;-</span><span class="Constant"> 3</span>
-   <span class="Constant"> 13</span> <span class="Special">&lt;-</span><span class="Constant"> 6</span>  <span class="Comment"># inserted element</span>
-   <span class="Constant"> 20</span> <span class="Special">&lt;-</span><span class="Constant"> 3</span>  <span class="Comment"># then prev</span>
-   <span class="Constant"> 21</span> <span class="Special">&lt;-</span><span class="Constant"> 4</span>
-   <span class="Constant"> 22</span> <span class="Special">&lt;-</span><span class="Constant"> 5</span>
-   <span class="Constant"> 30</span> <span class="Special">&lt;-</span><span class="Constant"> 1</span>  <span class="Comment"># list back at start</span>
-  ]
-]
-
-<span class="muScenario">scenario</span> inserting-after-start-of-duplex-list [
-  <span class="Constant">local-scope</span>
-  list:&amp;:duplex-list:char <span class="Special">&lt;-</span> push<span class="Constant"> 3</span>,<span class="Constant"> 0</span>
-  list <span class="Special">&lt;-</span> push<span class="Constant"> 4</span>, list
-  list <span class="Special">&lt;-</span> push<span class="Constant"> 5</span>, list
-  run [
-    list <span class="Special">&lt;-</span> insert<span class="Constant"> 6</span>, list
-    <span class="Comment"># check structure like before</span>
-    list2:&amp;:duplex-list:char <span class="Special">&lt;-</span> copy list
-    10:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> first list2
-    list2 <span class="Special">&lt;-</span> next list2
-    11:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> first list2
-    list2 <span class="Special">&lt;-</span> next list2
-    12:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> first list2
-    list2 <span class="Special">&lt;-</span> next list2
-    13:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> first list2
-    list2 <span class="Special">&lt;-</span> prev list2
-    20:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> first list2
-    list2 <span class="Special">&lt;-</span> prev list2
-    21:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> first list2
-    list2 <span class="Special">&lt;-</span> prev list2
-    22:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> first list2
-    30:bool/<span class="Special">raw</span> <span class="Special">&lt;-</span> equal list, list2
-  ]
-  memory-should-contain [
-   <span class="Constant"> 10</span> <span class="Special">&lt;-</span><span class="Constant"> 5</span>  <span class="Comment"># scanning next</span>
-   <span class="Constant"> 11</span> <span class="Special">&lt;-</span><span class="Constant"> 6</span>  <span class="Comment"># inserted element</span>
-   <span class="Constant"> 12</span> <span class="Special">&lt;-</span><span class="Constant"> 4</span>
-   <span class="Constant"> 13</span> <span class="Special">&lt;-</span><span class="Constant"> 3</span>
-   <span class="Constant"> 20</span> <span class="Special">&lt;-</span><span class="Constant"> 4</span>  <span class="Comment"># then prev</span>
-   <span class="Constant"> 21</span> <span class="Special">&lt;-</span><span class="Constant"> 6</span>
-   <span class="Constant"> 22</span> <span class="Special">&lt;-</span><span class="Constant"> 5</span>
-   <span class="Constant"> 30</span> <span class="Special">&lt;-</span><span class="Constant"> 1</span>  <span class="Comment"># list back at start</span>
-  ]
-]
-
-<span class="Comment"># remove 'x' from its surrounding list 'in'</span>
-<span class="Comment">#</span>
-<span class="Comment"># Returns null if and only if list is empty. Beware: in that case any other</span>
-<span class="Comment"># pointers to the head are now invalid.</span>
-<span class="muRecipe">def</span> remove x:&amp;:duplex-list:_elem/contained-in:in, in:&amp;:duplex-list:_elem<span class="muRecipe"> -&gt; </span>in:&amp;:duplex-list:_elem [
-  <span class="Constant">local-scope</span>
-  <span class="Constant">load-ingredients</span>
-  <span class="Comment"># if 'x' is null, return</span>
-  <span class="muControl">return-unless</span> x
-  next-node:&amp;:duplex-list:_elem <span class="Special">&lt;-</span> get *x, <span class="Constant">next:offset</span>
-  prev-node:&amp;:duplex-list:_elem <span class="Special">&lt;-</span> get *x, <span class="Constant">prev:offset</span>
-  <span class="Comment"># null x's pointers</span>
-  *x <span class="Special">&lt;-</span> put *x, <span class="Constant">next:offset</span>,<span class="Constant"> 0</span>
-  *x <span class="Special">&lt;-</span> put *x, <span class="Constant">prev:offset</span>,<span class="Constant"> 0</span>
-  <span class="Comment"># if next-node is not null, set its prev pointer</span>
-  <span class="Delimiter">{</span>
-    <span class="muControl">break-unless</span> next-node
-    *next-node <span class="Special">&lt;-</span> put *next-node, <span class="Constant">prev:offset</span>, prev-node
-  <span class="Delimiter">}</span>
-  <span class="Comment"># if prev-node is not null, set its next pointer and return</span>
-  <span class="Delimiter">{</span>
-    <span class="muControl">break-unless</span> prev-node
-    *prev-node <span class="Special">&lt;-</span> put *prev-node, <span class="Constant">next:offset</span>, next-node
-    <span class="muControl">return</span>
-  <span class="Delimiter">}</span>
-  <span class="Comment"># if prev-node is null, then we removed the head node at 'in'</span>
-  <span class="Comment"># return the new head rather than the old 'in'</span>
-  <span class="muControl">return</span> next-node
-]
-
-<span class="muScenario">scenario</span> removing-from-duplex-list [
-  <span class="Constant">local-scope</span>
-  list:&amp;:duplex-list:char <span class="Special">&lt;-</span> push<span class="Constant"> 3</span>,<span class="Constant"> 0</span>
-  list <span class="Special">&lt;-</span> push<span class="Constant"> 4</span>, list
-  list <span class="Special">&lt;-</span> push<span class="Constant"> 5</span>, list
-  run [
-    list2:&amp;:duplex-list:char <span class="Special">&lt;-</span> next list  <span class="Comment"># second element</span>
-    list <span class="Special">&lt;-</span> remove list2, list
-    10:bool/<span class="Special">raw</span> <span class="Special">&lt;-</span> equal list2,<span class="Constant"> 0</span>
-    <span class="Comment"># check structure like before</span>
-    list2 <span class="Special">&lt;-</span> copy list
-    11:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> first list2
-    list2 <span class="Special">&lt;-</span> next list2
-    12:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> first list2
-    20:&amp;:duplex-list:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> next list2
-    list2 <span class="Special">&lt;-</span> prev list2
-    30:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> first list2
-    40:bool/<span class="Special">raw</span> <span class="Special">&lt;-</span> equal list, list2
-  ]
-  memory-should-contain [
-   <span class="Constant"> 10</span> <span class="Special">&lt;-</span><span class="Constant"> 0</span>  <span class="Comment"># remove returned non-null</span>
-   <span class="Constant"> 11</span> <span class="Special">&lt;-</span><span class="Constant"> 5</span>  <span class="Comment"># scanning next, skipping deleted element</span>
-   <span class="Constant"> 12</span> <span class="Special">&lt;-</span><span class="Constant"> 3</span>
-   <span class="Constant"> 20</span> <span class="Special">&lt;-</span><span class="Constant"> 0</span>  <span class="Comment"># no more elements</span>
-   <span class="Constant"> 30</span> <span class="Special">&lt;-</span><span class="Constant"> 5</span>  <span class="Comment"># prev of final element</span>
-   <span class="Constant"> 40</span> <span class="Special">&lt;-</span><span class="Constant"> 1</span>  <span class="Comment"># list back at start</span>
-  ]
-]
-
-<span class="muScenario">scenario</span> removing-from-start-of-duplex-list [
-  <span class="Constant">local-scope</span>
-  list:&amp;:duplex-list:char <span class="Special">&lt;-</span> push<span class="Constant"> 3</span>,<span class="Constant"> 0</span>
-  list <span class="Special">&lt;-</span> push<span class="Constant"> 4</span>, list
-  list <span class="Special">&lt;-</span> push<span class="Constant"> 5</span>, list
-  run [
-    list <span class="Special">&lt;-</span> remove list, list
-    <span class="Comment"># check structure like before</span>
-    list2:&amp;:duplex-list:char <span class="Special">&lt;-</span> copy list
-    10:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> first list2
-    list2 <span class="Special">&lt;-</span> next list2
-    11:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> first list2
-    20:&amp;:duplex-list:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> next list2
-    list2 <span class="Special">&lt;-</span> prev list2
-    30:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> first list2
-    40:bool/<span class="Special">raw</span> <span class="Special">&lt;-</span> equal list, list2
-  ]
-  memory-should-contain [
-   <span class="Constant"> 10</span> <span class="Special">&lt;-</span><span class="Constant"> 4</span>  <span class="Comment"># scanning next, skipping deleted element</span>
-   <span class="Constant"> 11</span> <span class="Special">&lt;-</span><span class="Constant"> 3</span>
-   <span class="Constant"> 20</span> <span class="Special">&lt;-</span><span class="Constant"> 0</span>  <span class="Comment"># no more elements</span>
-   <span class="Constant"> 30</span> <span class="Special">&lt;-</span><span class="Constant"> 4</span>  <span class="Comment"># prev of final element</span>
-   <span class="Constant"> 40</span> <span class="Special">&lt;-</span><span class="Constant"> 1</span>  <span class="Comment"># list back at start</span>
-  ]
-]
-
-<span class="muScenario">scenario</span> removing-from-end-of-duplex-list [
-  <span class="Constant">local-scope</span>
-  list:&amp;:duplex-list:char <span class="Special">&lt;-</span> push<span class="Constant"> 3</span>,<span class="Constant"> 0</span>
-  list <span class="Special">&lt;-</span> push<span class="Constant"> 4</span>, list
-  list <span class="Special">&lt;-</span> push<span class="Constant"> 5</span>, list
-  run [
-    <span class="Comment"># delete last element</span>
-    list2:&amp;:duplex-list:char <span class="Special">&lt;-</span> next list
-    list2 <span class="Special">&lt;-</span> next list2
-    list <span class="Special">&lt;-</span> remove list2, list
-    10:bool/<span class="Special">raw</span> <span class="Special">&lt;-</span> equal list2,<span class="Constant"> 0</span>
-    <span class="Comment"># check structure like before</span>
-    list2 <span class="Special">&lt;-</span> copy list
-    11:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> first list2
-    list2 <span class="Special">&lt;-</span> next list2
-    12:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> first list2
-    20:&amp;:duplex-list:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> next list2
-    list2 <span class="Special">&lt;-</span> prev list2
-    30:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> first list2
-    40:bool/<span class="Special">raw</span> <span class="Special">&lt;-</span> equal list, list2
-  ]
-  memory-should-contain [
-   <span class="Constant"> 10</span> <span class="Special">&lt;-</span><span class="Constant"> 0</span>  <span class="Comment"># remove returned non-null</span>
-   <span class="Constant"> 11</span> <span class="Special">&lt;-</span><span class="Constant"> 5</span>  <span class="Comment"># scanning next, skipping deleted element</span>
-   <span class="Constant"> 12</span> <span class="Special">&lt;-</span><span class="Constant"> 4</span>
-   <span class="Constant"> 20</span> <span class="Special">&lt;-</span><span class="Constant"> 0</span>  <span class="Comment"># no more elements</span>
-   <span class="Constant"> 30</span> <span class="Special">&lt;-</span><span class="Constant"> 5</span>  <span class="Comment"># prev of final element</span>
-   <span class="Constant"> 40</span> <span class="Special">&lt;-</span><span class="Constant"> 1</span>  <span class="Comment"># list back at start</span>
-  ]
-]
-
-<span class="muScenario">scenario</span> removing-from-singleton-duplex-list [
-  <span class="Constant">local-scope</span>
-  list:&amp;:duplex-list:char <span class="Special">&lt;-</span> push<span class="Constant"> 3</span>,<span class="Constant"> 0</span>
-  run [
-    list <span class="Special">&lt;-</span> remove list, list
-    1:num/<span class="Special">raw</span> <span class="Special">&lt;-</span> copy list
-  ]
-  memory-should-contain [
-   <span class="Constant"> 1</span> <span class="Special">&lt;-</span><span class="Constant"> 0</span>  <span class="Comment"># back to an empty list</span>
-  ]
-]
-
-<span class="Comment"># remove values between 'start' and 'end' (both exclusive).</span>
-<span class="Comment"># also clear pointers back out from start/end for hygiene.</span>
-<span class="Comment"># set end to 0 to delete everything past start.</span>
-<span class="Comment"># can't set start to 0 to delete everything before end, because there's no</span>
-<span class="Comment"># clean way to return the new head pointer.</span>
-<span class="muRecipe">def</span> remove-between start:&amp;:duplex-list:_elem, end:&amp;:duplex-list:_elem/contained-in:start<span class="muRecipe"> -&gt; </span>start:&amp;:duplex-list:_elem [
-  <span class="Constant">local-scope</span>
-  <span class="Constant">load-ingredients</span>
-  next:&amp;:duplex-list:_elem <span class="Special">&lt;-</span> get *start, <span class="Constant">next:offset</span>
-  nothing-to-delete?:bool <span class="Special">&lt;-</span> equal next, end
-  <span class="muControl">return-if</span> nothing-to-delete?
-  assert next, <span class="Constant">[malformed duplex list]</span>
-  <span class="Comment"># start-&gt;next-&gt;prev = 0</span>
-  <span class="Comment"># start-&gt;next = end</span>
-  *next <span class="Special">&lt;-</span> put *next, <span class="Constant">prev:offset</span>,<span class="Constant"> 0</span>
-  *start <span class="Special">&lt;-</span> put *start, <span class="Constant">next:offset</span>, end
-  <span class="muControl">return-unless</span> end
-  <span class="Comment"># end-&gt;prev-&gt;next = 0</span>
-  <span class="Comment"># end-&gt;prev = start</span>
-  prev:&amp;:duplex-list:_elem <span class="Special">&lt;-</span> get *end, <span class="Constant">prev:offset</span>
-  assert prev, <span class="Constant">[malformed duplex list - 2]</span>
-  *prev <span class="Special">&lt;-</span> put *prev, <span class="Constant">next:offset</span>,<span class="Constant"> 0</span>
-  *end <span class="Special">&lt;-</span> put *end, <span class="Constant">prev:offset</span>, start
-]
-
-<span class="muScenario">scenario</span> remove-range [
-  <span class="Comment"># construct a duplex list with six elements [13, 14, 15, 16, 17, 18]</span>
-  <span class="Constant">local-scope</span>
-  list:&amp;:duplex-list:char <span class="Special">&lt;-</span> push<span class="Constant"> 18</span>,<span class="Constant"> 0</span>
-  list <span class="Special">&lt;-</span> push<span class="Constant"> 17</span>, list
-  list <span class="Special">&lt;-</span> push<span class="Constant"> 16</span>, list
-  list <span class="Special">&lt;-</span> push<span class="Constant"> 15</span>, list
-  list <span class="Special">&lt;-</span> push<span class="Constant"> 14</span>, list
-  list <span class="Special">&lt;-</span> push<span class="Constant"> 13</span>, list
-  run [
-    <span class="Comment"># delete 16 onwards</span>
-    <span class="Comment"># first pointer: to the third element</span>
-    list2:&amp;:duplex-list:char <span class="Special">&lt;-</span> next list
-    list2 <span class="Special">&lt;-</span> next list2
-    list2 <span class="Special">&lt;-</span> remove-between list2,<span class="Constant"> 0</span>
-    <span class="Comment"># now check the list</span>
-    10:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> get *list, <span class="Constant">value:offset</span>
-    list <span class="Special">&lt;-</span> next list
-    11:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> get *list, <span class="Constant">value:offset</span>
-    list <span class="Special">&lt;-</span> next list
-    12:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> get *list, <span class="Constant">value:offset</span>
-    20:&amp;:duplex-list:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> next list
-  ]
-  memory-should-contain [
-   <span class="Constant"> 10</span> <span class="Special">&lt;-</span><span class="Constant"> 13</span>
-   <span class="Constant"> 11</span> <span class="Special">&lt;-</span><span class="Constant"> 14</span>
-   <span class="Constant"> 12</span> <span class="Special">&lt;-</span><span class="Constant"> 15</span>
-   <span class="Constant"> 20</span> <span class="Special">&lt;-</span><span class="Constant"> 0</span>
-  ]
-]
-
-<span class="muScenario">scenario</span> remove-range-to-final [
-  <span class="Constant">local-scope</span>
-  <span class="Comment"># construct a duplex list with six elements [13, 14, 15, 16, 17, 18]</span>
-  list:&amp;:duplex-list:char <span class="Special">&lt;-</span> push<span class="Constant"> 18</span>,<span class="Constant"> 0</span>
-  list <span class="Special">&lt;-</span> push<span class="Constant"> 17</span>, list
-  list <span class="Special">&lt;-</span> push<span class="Constant"> 16</span>, list
-  list <span class="Special">&lt;-</span> push<span class="Constant"> 15</span>, list
-  list <span class="Special">&lt;-</span> push<span class="Constant"> 14</span>, list
-  list <span class="Special">&lt;-</span> push<span class="Constant"> 13</span>, list
-  run [
-    <span class="Comment"># delete 15, 16 and 17</span>
-    <span class="Comment"># start pointer: to the second element</span>
-    list2:&amp;:duplex-list:char <span class="Special">&lt;-</span> next list
-    <span class="Comment"># end pointer: to the last (sixth) element</span>
-    end:&amp;:duplex-list:char <span class="Special">&lt;-</span> next list2
-    end <span class="Special">&lt;-</span> next end
-    end <span class="Special">&lt;-</span> next end
-    end <span class="Special">&lt;-</span> next end
-    remove-between list2, end
-    <span class="Comment"># now check the list</span>
-    10:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> get *list, <span class="Constant">value:offset</span>
-    list <span class="Special">&lt;-</span> next list
-    11:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> get *list, <span class="Constant">value:offset</span>
-    list <span class="Special">&lt;-</span> next list
-    12:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> get *list, <span class="Constant">value:offset</span>
-    20:&amp;:duplex-list:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> next list
-  ]
-  memory-should-contain [
-   <span class="Constant"> 10</span> <span class="Special">&lt;-</span><span class="Constant"> 13</span>
-   <span class="Constant"> 11</span> <span class="Special">&lt;-</span><span class="Constant"> 14</span>
-   <span class="Constant"> 12</span> <span class="Special">&lt;-</span><span class="Constant"> 18</span>
-   <span class="Constant"> 20</span> <span class="Special">&lt;-</span><span class="Constant"> 0</span>  <span class="Comment"># no more elements</span>
-  ]
-]
-
-<span class="muScenario">scenario</span> remove-range-empty [
-  <span class="Constant">local-scope</span>
-  <span class="Comment"># construct a duplex list with three elements [13, 14, 15]</span>
-  list:&amp;:duplex-list:char <span class="Special">&lt;-</span> push<span class="Constant"> 15</span>,<span class="Constant"> 0</span>
-  list <span class="Special">&lt;-</span> push<span class="Constant"> 14</span>, list
-  list <span class="Special">&lt;-</span> push<span class="Constant"> 13</span>, list
-  run [
-    <span class="Comment"># delete between first and second element (i.e. nothing)</span>
-    list2:&amp;:duplex-list:char <span class="Special">&lt;-</span> next list
-    remove-between list, list2
-    <span class="Comment"># now check the list</span>
-    10:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> get *list, <span class="Constant">value:offset</span>
-    list <span class="Special">&lt;-</span> next list
-    11:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> get *list, <span class="Constant">value:offset</span>
-    list <span class="Special">&lt;-</span> next list
-    12:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> get *list, <span class="Constant">value:offset</span>
-    20:&amp;:duplex-list:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> next list
-  ]
-  <span class="Comment"># no change</span>
-  memory-should-contain [
-   <span class="Constant"> 10</span> <span class="Special">&lt;-</span><span class="Constant"> 13</span>
-   <span class="Constant"> 11</span> <span class="Special">&lt;-</span><span class="Constant"> 14</span>
-   <span class="Constant"> 12</span> <span class="Special">&lt;-</span><span class="Constant"> 15</span>
-   <span class="Constant"> 20</span> <span class="Special">&lt;-</span><span class="Constant"> 0</span>
-  ]
-]
-
-<span class="muScenario">scenario</span> remove-range-to-end [
-  <span class="Constant">local-scope</span>
-  <span class="Comment"># construct a duplex list with six elements [13, 14, 15, 16, 17, 18]</span>
-  list:&amp;:duplex-list:char <span class="Special">&lt;-</span> push<span class="Constant"> 18</span>,<span class="Constant"> 0</span>
-  list <span class="Special">&lt;-</span> push<span class="Constant"> 17</span>, list
-  list <span class="Special">&lt;-</span> push<span class="Constant"> 16</span>, list
-  list <span class="Special">&lt;-</span> push<span class="Constant"> 15</span>, list
-  list <span class="Special">&lt;-</span> push<span class="Constant"> 14</span>, list
-  list <span class="Special">&lt;-</span> push<span class="Constant"> 13</span>, list
-  run [
-    <span class="Comment"># remove the third element and beyond</span>
-    list2:&amp;:duplex-list:char <span class="Special">&lt;-</span> next list
-    remove-between list2,<span class="Constant"> 0</span>
-    <span class="Comment"># now check the list</span>
-    10:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> get *list, <span class="Constant">value:offset</span>
-    list <span class="Special">&lt;-</span> next list
-    11:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> get *list, <span class="Constant">value:offset</span>
-    20:&amp;:duplex-list:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> next list
-  ]
-  memory-should-contain [
-   <span class="Constant"> 10</span> <span class="Special">&lt;-</span><span class="Constant"> 13</span>
-   <span class="Constant"> 11</span> <span class="Special">&lt;-</span><span class="Constant"> 14</span>
-   <span class="Constant"> 20</span> <span class="Special">&lt;-</span><span class="Constant"> 0</span>
-  ]
-]
-
-<span class="Comment"># insert list beginning at 'new' after 'in'</span>
-<span class="muRecipe">def</span> insert-range in:&amp;:duplex-list:_elem, start:&amp;:duplex-list:_elem/contained-in:in<span class="muRecipe"> -&gt; </span>in:&amp;:duplex-list:_elem [
-  <span class="Constant">local-scope</span>
-  <span class="Constant">load-ingredients</span>
-  <span class="muControl">return-unless</span> in
-  <span class="muControl">return-unless</span> start
-  end:&amp;:duplex-list:_elem <span class="Special">&lt;-</span> copy start
-  <span class="Delimiter">{</span>
-    next:&amp;:duplex-list:_elem <span class="Special">&lt;-</span> next end/insert-range
-    <span class="muControl">break-unless</span> next
-    end <span class="Special">&lt;-</span> copy next
-    <span class="muControl">loop</span>
-  <span class="Delimiter">}</span>
-  next:&amp;:duplex-list:_elem <span class="Special">&lt;-</span> next in
-  *end <span class="Special">&lt;-</span> put *end, <span class="Constant">next:offset</span>, next
-  <span class="Delimiter">{</span>
-    <span class="muControl">break-unless</span> next
-    *next <span class="Special">&lt;-</span> put *next, <span class="Constant">prev:offset</span>, end
-  <span class="Delimiter">}</span>
-  *in <span class="Special">&lt;-</span> put *in, <span class="Constant">next:offset</span>, start
-  *start <span class="Special">&lt;-</span> put *start, <span class="Constant">prev:offset</span>, in
-]
-
-<span class="muRecipe">def</span> append in:&amp;:duplex-list:_elem, new:&amp;:duplex-list:_elem/contained-in:in<span class="muRecipe"> -&gt; </span>in:&amp;:duplex-list:_elem [
-  <span class="Constant">local-scope</span>
-  <span class="Constant">load-ingredients</span>
-  last:&amp;:duplex-list:_elem <span class="Special">&lt;-</span> last in
-  *last <span class="Special">&lt;-</span> put *last, <span class="Constant">next:offset</span>, new
-  <span class="muControl">return-unless</span> new
-  *new <span class="Special">&lt;-</span> put *new, <span class="Constant">prev:offset</span>, last
-]
-
-<span class="muRecipe">def</span> last in:&amp;:duplex-list:_elem<span class="muRecipe"> -&gt; </span>result:&amp;:duplex-list:_elem [
-  <span class="Constant">local-scope</span>
-  <span class="Constant">load-ingredients</span>
-  result <span class="Special">&lt;-</span> copy in
-  <span class="Delimiter">{</span>
-    next:&amp;:duplex-list:_elem <span class="Special">&lt;-</span> next result
-    <span class="muControl">break-unless</span> next
-    result <span class="Special">&lt;-</span> copy next
-    <span class="muControl">loop</span>
-  <span class="Delimiter">}</span>
-]
-
-<span class="Comment"># helper for debugging</span>
-<span class="muRecipe">def</span> dump-from x:&amp;:duplex-list:_elem [
-  <span class="Constant">local-scope</span>
-  <span class="Constant">load-ingredients</span>
-  $print x, <span class="Constant">[: ]</span>
-  <span class="Delimiter">{</span>
-    <span class="muControl">break-unless</span> x
-    c:_elem <span class="Special">&lt;-</span> get *x, <span class="Constant">value:offset</span>
-    $print c, <span class="Constant">[ ]</span>
-    x <span class="Special">&lt;-</span> next x
-    <span class="Delimiter">{</span>
-      is-newline?:bool <span class="Special">&lt;-</span> equal c, <span class="Constant">10/newline</span>
-      <span class="muControl">break-unless</span> is-newline?
-      $print <span class="Constant">10/newline</span>
-      $print x, <span class="Constant">[: ]</span>
-    <span class="Delimiter">}</span>
-    <span class="muControl">loop</span>
-  <span class="Delimiter">}</span>
-  $print <span class="Constant">10/newline</span>, <span class="Constant">[---]</span>, <span class="Constant">10/newline</span>
-]
+<a name="L1"></a><span id="L1" class="LineNr">  1 </span><span class="Comment"># A doubly linked list permits bidirectional traversal.</span>
+<a name="L2"></a><span id="L2" class="LineNr">  2 </span>
+<a name="L3"></a><span id="L3" class="LineNr">  3 </span><span class="muData">container</span> duplex-list:_elem [
+<a name="L4"></a><span id="L4" class="LineNr">  4 </span>  value:_elem
+<a name="L5"></a><span id="L5" class="LineNr">  5 </span>  next:&amp;:duplex-list:_elem
+<a name="L6"></a><span id="L6" class="LineNr">  6 </span>  prev:&amp;:duplex-list:_elem
+<a name="L7"></a><span id="L7" class="LineNr">  7 </span>]
+<a name="L8"></a><span id="L8" class="LineNr">  8 </span>
+<a name="L9"></a><span id="L9" class="LineNr">  9 </span><span class="Comment"># should I say in/contained-in:result, allow ingredients to refer to products?</span>
+<a name="L10"></a><span id="L10" class="LineNr"> 10 </span><span class="muRecipe">def</span> push x:_elem, in:&amp;:duplex-list:_elem<span class="muRecipe"> -&gt; </span>in:&amp;:duplex-list:_elem [
+<a name="L11"></a><span id="L11" class="LineNr"> 11 </span>  <span class="Constant">local-scope</span>
+<a name="L12"></a><span id="L12" class="LineNr"> 12 </span>  <span class="Constant">load-ingredients</span>
+<a name="L13"></a><span id="L13" class="LineNr"> 13 </span>  result:&amp;:duplex-list:_elem <span class="Special">&lt;-</span> new <span class="Delimiter">{</span>(duplex-list _elem): type<span class="Delimiter">}</span>
+<a name="L14"></a><span id="L14" class="LineNr"> 14 </span>  *result <span class="Special">&lt;-</span> merge x, in,<span class="Constant"> 0</span>
+<a name="L15"></a><span id="L15" class="LineNr"> 15 </span>  <span class="Delimiter">{</span>
+<a name="L16"></a><span id="L16" class="LineNr"> 16 </span>    <span class="muControl">break-unless</span> in
+<a name="L17"></a><span id="L17" class="LineNr"> 17 </span>    *in <span class="Special">&lt;-</span> put *in, <span class="Constant">prev:offset</span>, result
+<a name="L18"></a><span id="L18" class="LineNr"> 18 </span>  <span class="Delimiter">}</span>
+<a name="L19"></a><span id="L19" class="LineNr"> 19 </span>  <span class="muControl">return</span> result  <span class="Comment"># needed explicitly because we need to replace 'in' with 'result'</span>
+<a name="L20"></a><span id="L20" class="LineNr"> 20 </span>]
+<a name="L21"></a><span id="L21" class="LineNr"> 21 </span>
+<a name="L22"></a><span id="L22" class="LineNr"> 22 </span><span class="muRecipe">def</span> first in:&amp;:duplex-list:_elem<span class="muRecipe"> -&gt; </span>result:_elem [
+<a name="L23"></a><span id="L23" class="LineNr"> 23 </span>  <span class="Constant">local-scope</span>
+<a name="L24"></a><span id="L24" class="LineNr"> 24 </span>  <span class="Constant">load-ingredients</span>
+<a name="L25"></a><span id="L25" class="LineNr"> 25 </span>  <span class="muControl">return-unless</span> in,<span class="Constant"> 0</span>
+<a name="L26"></a><span id="L26" class="LineNr"> 26 </span>  result <span class="Special">&lt;-</span> get *in, <span class="Constant">value:offset</span>
+<a name="L27"></a><span id="L27" class="LineNr"> 27 </span>]
+<a name="L28"></a><span id="L28" class="LineNr"> 28 </span>
+<a name="L29"></a><span id="L29" class="LineNr"> 29 </span><span class="muRecipe">def</span> next in:&amp;:duplex-list:_elem<span class="muRecipe"> -&gt; </span>result:&amp;:duplex-list:_elem/contained-in:in [
+<a name="L30"></a><span id="L30" class="LineNr"> 30 </span>  <span class="Constant">local-scope</span>
+<a name="L31"></a><span id="L31" class="LineNr"> 31 </span>  <span class="Constant">load-ingredients</span>
+<a name="L32"></a><span id="L32" class="LineNr"> 32 </span>  <span class="muControl">return-unless</span> in,<span class="Constant"> 0</span>
+<a name="L33"></a><span id="L33" class="LineNr"> 33 </span>  result <span class="Special">&lt;-</span> get *in, <span class="Constant">next:offset</span>
+<a name="L34"></a><span id="L34" class="LineNr"> 34 </span>]
+<a name="L35"></a><span id="L35" class="LineNr"> 35 </span>
+<a name="L36"></a><span id="L36" class="LineNr"> 36 </span><span class="muRecipe">def</span> prev in:&amp;:duplex-list:_elem<span class="muRecipe"> -&gt; </span>result:&amp;:duplex-list:_elem/contained-in:in [
+<a name="L37"></a><span id="L37" class="LineNr"> 37 </span>  <span class="Constant">local-scope</span>
+<a name="L38"></a><span id="L38" class="LineNr"> 38 </span>  <span class="Constant">load-ingredients</span>
+<a name="L39"></a><span id="L39" class="LineNr"> 39 </span>  <span class="muControl">return-unless</span> in,<span class="Constant"> 0</span>
+<a name="L40"></a><span id="L40" class="LineNr"> 40 </span>  result <span class="Special">&lt;-</span> get *in, <span class="Constant">prev:offset</span>
+<a name="L41"></a><span id="L41" class="LineNr"> 41 </span>  <span class="muControl">return</span> result
+<a name="L42"></a><span id="L42" class="LineNr"> 42 </span>]
+<a name="L43"></a><span id="L43" class="LineNr"> 43 </span>
+<a name="L44"></a><span id="L44" class="LineNr"> 44 </span><span class="muScenario">scenario</span> duplex-list-handling [
+<a name="L45"></a><span id="L45" class="LineNr"> 45 </span>  run [
+<a name="L46"></a><span id="L46" class="LineNr"> 46 </span>    <span class="Constant">local-scope</span>
+<a name="L47"></a><span id="L47" class="LineNr"> 47 </span>    <span class="Comment"># reserve locations 0-9 to check for missing null check</span>
+<a name="L48"></a><span id="L48" class="LineNr"> 48 </span>    10:num/<span class="Special">raw</span> <span class="Special">&lt;-</span> copy<span class="Constant"> 34</span>
+<a name="L49"></a><span id="L49" class="LineNr"> 49 </span>    11:num/<span class="Special">raw</span> <span class="Special">&lt;-</span> copy<span class="Constant"> 35</span>
+<a name="L50"></a><span id="L50" class="LineNr"> 50 </span>    list:&amp;:duplex-list:char <span class="Special">&lt;-</span> push<span class="Constant"> 3</span>,<span class="Constant"> 0</span>
+<a name="L51"></a><span id="L51" class="LineNr"> 51 </span>    list <span class="Special">&lt;-</span> push<span class="Constant"> 4</span>, list
+<a name="L52"></a><span id="L52" class="LineNr"> 52 </span>    list <span class="Special">&lt;-</span> push<span class="Constant"> 5</span>, list
+<a name="L53"></a><span id="L53" class="LineNr"> 53 </span>    list2:&amp;:duplex-list:char <span class="Special">&lt;-</span> copy list
+<a name="L54"></a><span id="L54" class="LineNr"> 54 </span>    20:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> first list2
+<a name="L55"></a><span id="L55" class="LineNr"> 55 </span>    list2 <span class="Special">&lt;-</span> next list2
+<a name="L56"></a><span id="L56" class="LineNr"> 56 </span>    21:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> first list2
+<a name="L57"></a><span id="L57" class="LineNr"> 57 </span>    list2 <span class="Special">&lt;-</span> next list2
+<a name="L58"></a><span id="L58" class="LineNr"> 58 </span>    22:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> first list2
+<a name="L59"></a><span id="L59" class="LineNr"> 59 </span>    30:&amp;:duplex-list:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> next list2
+<a name="L60"></a><span id="L60" class="LineNr"> 60 </span>    31:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> first 30:&amp;:duplex-list:char/<span class="Special">raw</span>
+<a name="L61"></a><span id="L61" class="LineNr"> 61 </span>    32:&amp;:duplex-list:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> next 30:&amp;:duplex-list:char/<span class="Special">raw</span>
+<a name="L62"></a><span id="L62" class="LineNr"> 62 </span>    33:&amp;:duplex-list:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> prev 30:&amp;:duplex-list:char/<span class="Special">raw</span>
+<a name="L63"></a><span id="L63" class="LineNr"> 63 </span>    list2 <span class="Special">&lt;-</span> prev list2
+<a name="L64"></a><span id="L64" class="LineNr"> 64 </span>    40:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> first list2
+<a name="L65"></a><span id="L65" class="LineNr"> 65 </span>    list2 <span class="Special">&lt;-</span> prev list2
+<a name="L66"></a><span id="L66" class="LineNr"> 66 </span>    41:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> first list2
+<a name="L67"></a><span id="L67" class="LineNr"> 67 </span>    50:bool/<span class="Special">raw</span> <span class="Special">&lt;-</span> equal list, list2
+<a name="L68"></a><span id="L68" class="LineNr"> 68 </span>  ]
+<a name="L69"></a><span id="L69" class="LineNr"> 69 </span>  memory-should-contain [
+<a name="L70"></a><span id="L70" class="LineNr"> 70 </span>   <span class="Constant"> 0</span> <span class="Special">&lt;-</span><span class="Constant"> 0</span>  <span class="Comment"># no modifications to null pointers</span>
+<a name="L71"></a><span id="L71" class="LineNr"> 71 </span>   <span class="Constant"> 10</span> <span class="Special">&lt;-</span><span class="Constant"> 34</span>
+<a name="L72"></a><span id="L72" class="LineNr"> 72 </span>   <span class="Constant"> 11</span> <span class="Special">&lt;-</span><span class="Constant"> 35</span>
+<a name="L73"></a><span id="L73" class="LineNr"> 73 </span>   <span class="Constant"> 20</span> <span class="Special">&lt;-</span><span class="Constant"> 5</span>  <span class="Comment"># scanning next</span>
+<a name="L74"></a><span id="L74" class="LineNr"> 74 </span>   <span class="Constant"> 21</span> <span class="Special">&lt;-</span><span class="Constant"> 4</span>
+<a name="L75"></a><span id="L75" class="LineNr"> 75 </span>   <span class="Constant"> 22</span> <span class="Special">&lt;-</span><span class="Constant"> 3</span>
+<a name="L76"></a><span id="L76" class="LineNr"> 76 </span>   <span class="Constant"> 30</span> <span class="Special">&lt;-</span><span class="Constant"> 0</span>  <span class="Comment"># null</span>
+<a name="L77"></a><span id="L77" class="LineNr"> 77 </span>   <span class="Constant"> 31</span> <span class="Special">&lt;-</span><span class="Constant"> 0</span>  <span class="Comment"># first of null</span>
+<a name="L78"></a><span id="L78" class="LineNr"> 78 </span>   <span class="Constant"> 32</span> <span class="Special">&lt;-</span><span class="Constant"> 0</span>  <span class="Comment"># next of null</span>
+<a name="L79"></a><span id="L79" class="LineNr"> 79 </span>   <span class="Constant"> 33</span> <span class="Special">&lt;-</span><span class="Constant"> 0</span>  <span class="Comment"># prev of null</span>
+<a name="L80"></a><span id="L80" class="LineNr"> 80 </span>   <span class="Constant"> 40</span> <span class="Special">&lt;-</span><span class="Constant"> 4</span>  <span class="Comment"># then start scanning prev</span>
+<a name="L81"></a><span id="L81" class="LineNr"> 81 </span>   <span class="Constant"> 41</span> <span class="Special">&lt;-</span><span class="Constant"> 5</span>
+<a name="L82"></a><span id="L82" class="LineNr"> 82 </span>   <span class="Constant"> 50</span> <span class="Special">&lt;-</span><span class="Constant"> 1</span>  <span class="Comment"># list back at start</span>
+<a name="L83"></a><span id="L83" class="LineNr"> 83 </span>  ]
+<a name="L84"></a><span id="L84" class="LineNr"> 84 </span>]
+<a name="L85"></a><span id="L85" class="LineNr"> 85 </span>
+<a name="L86"></a><span id="L86" class="LineNr"> 86 </span><span class="Comment"># insert 'x' after 'in'</span>
+<a name="L87"></a><span id="L87" class="LineNr"> 87 </span><span class="muRecipe">def</span> insert x:_elem, in:&amp;:duplex-list:_elem<span class="muRecipe"> -&gt; </span>in:&amp;:duplex-list:_elem [
+<a name="L88"></a><span id="L88" class="LineNr"> 88 </span>  <span class="Constant">local-scope</span>
+<a name="L89"></a><span id="L89" class="LineNr"> 89 </span>  <span class="Constant">load-ingredients</span>
+<a name="L90"></a><span id="L90" class="LineNr"> 90 </span>  new-node:&amp;:duplex-list:_elem <span class="Special">&lt;-</span> new <span class="Delimiter">{</span>(duplex-list _elem): type<span class="Delimiter">}</span>
+<a name="L91"></a><span id="L91" class="LineNr"> 91 </span>  *new-node <span class="Special">&lt;-</span> put *new-node, <span class="Constant">value:offset</span>, x
+<a name="L92"></a><span id="L92" class="LineNr"> 92 </span>  <span class="Comment"># save old next before changing it</span>
+<a name="L93"></a><span id="L93" class="LineNr"> 93 </span>  next-node:&amp;:duplex-list:_elem <span class="Special">&lt;-</span> get *in, <span class="Constant">next:offset</span>
+<a name="L94"></a><span id="L94" class="LineNr"> 94 </span>  *in <span class="Special">&lt;-</span> put *in, <span class="Constant">next:offset</span>, new-node
+<a name="L95"></a><span id="L95" class="LineNr"> 95 </span>  *new-node <span class="Special">&lt;-</span> put *new-node, <span class="Constant">prev:offset</span>, in
+<a name="L96"></a><span id="L96" class="LineNr"> 96 </span>  *new-node <span class="Special">&lt;-</span> put *new-node, <span class="Constant">next:offset</span>, next-node
+<a name="L97"></a><span id="L97" class="LineNr"> 97 </span>  <span class="muControl">return-unless</span> next-node
+<a name="L98"></a><span id="L98" class="LineNr"> 98 </span>  *next-node <span class="Special">&lt;-</span> put *next-node, <span class="Constant">prev:offset</span>, new-node
+<a name="L99"></a><span id="L99" class="LineNr"> 99 </span>]
+<a name="L100"></a><span id="L100" class="LineNr">100 </span>
+<a name="L101"></a><span id="L101" class="LineNr">101 </span><span class="muScenario">scenario</span> inserting-into-duplex-list [
+<a name="L102"></a><span id="L102" class="LineNr">102 </span>  <span class="Constant">local-scope</span>
+<a name="L103"></a><span id="L103" class="LineNr">103 </span>  list:&amp;:duplex-list:char <span class="Special">&lt;-</span> push<span class="Constant"> 3</span>,<span class="Constant"> 0</span>
+<a name="L104"></a><span id="L104" class="LineNr">104 </span>  list <span class="Special">&lt;-</span> push<span class="Constant"> 4</span>, list
+<a name="L105"></a><span id="L105" class="LineNr">105 </span>  list <span class="Special">&lt;-</span> push<span class="Constant"> 5</span>, list
+<a name="L106"></a><span id="L106" class="LineNr">106 </span>  run [
+<a name="L107"></a><span id="L107" class="LineNr">107 </span>    list2:&amp;:duplex-list:char <span class="Special">&lt;-</span> next list  <span class="Comment"># inside list</span>
+<a name="L108"></a><span id="L108" class="LineNr">108 </span>    list2 <span class="Special">&lt;-</span> insert<span class="Constant"> 6</span>, list2
+<a name="L109"></a><span id="L109" class="LineNr">109 </span>    <span class="Comment"># check structure like before</span>
+<a name="L110"></a><span id="L110" class="LineNr">110 </span>    list2 <span class="Special">&lt;-</span> copy list
+<a name="L111"></a><span id="L111" class="LineNr">111 </span>    10:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> first list2
+<a name="L112"></a><span id="L112" class="LineNr">112 </span>    list2 <span class="Special">&lt;-</span> next list2
+<a name="L113"></a><span id="L113" class="LineNr">113 </span>    11:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> first list2
+<a name="L114"></a><span id="L114" class="LineNr">114 </span>    list2 <span class="Special">&lt;-</span> next list2
+<a name="L115"></a><span id="L115" class="LineNr">115 </span>    12:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> first list2
+<a name="L116"></a><span id="L116" class="LineNr">116 </span>    list2 <span class="Special">&lt;-</span> next list2
+<a name="L117"></a><span id="L117" class="LineNr">117 </span>    13:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> first list2
+<a name="L118"></a><span id="L118" class="LineNr">118 </span>    list2 <span class="Special">&lt;-</span> prev list2
+<a name="L119"></a><span id="L119" class="LineNr">119 </span>    20:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> first list2
+<a name="L120"></a><span id="L120" class="LineNr">120 </span>    list2 <span class="Special">&lt;-</span> prev list2
+<a name="L121"></a><span id="L121" class="LineNr">121 </span>    21:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> first list2
+<a name="L122"></a><span id="L122" class="LineNr">122 </span>    list2 <span class="Special">&lt;-</span> prev list2
+<a name="L123"></a><span id="L123" class="LineNr">123 </span>    22:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> first list2
+<a name="L124"></a><span id="L124" class="LineNr">124 </span>    30:bool/<span class="Special">raw</span> <span class="Special">&lt;-</span> equal list, list2
+<a name="L125"></a><span id="L125" class="LineNr">125 </span>  ]
+<a name="L126"></a><span id="L126" class="LineNr">126 </span>  memory-should-contain [
+<a name="L127"></a><span id="L127" class="LineNr">127 </span>   <span class="Constant"> 10</span> <span class="Special">&lt;-</span><span class="Constant"> 5</span>  <span class="Comment"># scanning next</span>
+<a name="L128"></a><span id="L128" class="LineNr">128 </span>   <span class="Constant"> 11</span> <span class="Special">&lt;-</span><span class="Constant"> 4</span>
+<a name="L129"></a><span id="L129" class="LineNr">129 </span>   <span class="Constant"> 12</span> <span class="Special">&lt;-</span><span class="Constant"> 6</span>  <span class="Comment"># inserted element</span>
+<a name="L130"></a><span id="L130" class="LineNr">130 </span>   <span class="Constant"> 13</span> <span class="Special">&lt;-</span><span class="Constant"> 3</span>
+<a name="L131"></a><span id="L131" class="LineNr">131 </span>   <span class="Constant"> 20</span> <span class="Special">&lt;-</span><span class="Constant"> 6</span>  <span class="Comment"># then prev</span>
+<a name="L132"></a><span id="L132" class="LineNr">132 </span>   <span class="Constant"> 21</span> <span class="Special">&lt;-</span><span class="Constant"> 4</span>
+<a name="L133"></a><span id="L133" class="LineNr">133 </span>   <span class="Constant"> 22</span> <span class="Special">&lt;-</span><span class="Constant"> 5</span>
+<a name="L134"></a><span id="L134" class="LineNr">134 </span>   <span class="Constant"> 30</span> <span class="Special">&lt;-</span><span class="Constant"> 1</span>  <span class="Comment"># list back at start</span>
+<a name="L135"></a><span id="L135" class="LineNr">135 </span>  ]
+<a name="L136"></a><span id="L136" class="LineNr">136 </span>]
+<a name="L137"></a><span id="L137" class="LineNr">137 </span>
+<a name="L138"></a><span id="L138" class="LineNr">138 </span><span class="muScenario">scenario</span> inserting-at-end-of-duplex-list [
+<a name="L139"></a><span id="L139" class="LineNr">139 </span>  <span class="Constant">local-scope</span>
+<a name="L140"></a><span id="L140" class="LineNr">140 </span>  list:&amp;:duplex-list:char <span class="Special">&lt;-</span> push<span class="Constant"> 3</span>,<span class="Constant"> 0</span>
+<a name="L141"></a><span id="L141" class="LineNr">141 </span>  list <span class="Special">&lt;-</span> push<span class="Constant"> 4</span>, list
+<a name="L142"></a><span id="L142" class="LineNr">142 </span>  list <span class="Special">&lt;-</span> push<span class="Constant"> 5</span>, list
+<a name="L143"></a><span id="L143" class="LineNr">143 </span>  run [
+<a name="L144"></a><span id="L144" class="LineNr">144 </span>    list2:&amp;:duplex-list:char <span class="Special">&lt;-</span> next list  <span class="Comment"># inside list</span>
+<a name="L145"></a><span id="L145" class="LineNr">145 </span>    list2 <span class="Special">&lt;-</span> next list2  <span class="Comment"># now at end of list</span>
+<a name="L146"></a><span id="L146" class="LineNr">146 </span>    list2 <span class="Special">&lt;-</span> insert<span class="Constant"> 6</span>, list2
+<a name="L147"></a><span id="L147" class="LineNr">147 </span>    <span class="Comment"># check structure like before</span>
+<a name="L148"></a><span id="L148" class="LineNr">148 </span>    list2 <span class="Special">&lt;-</span> copy list
+<a name="L149"></a><span id="L149" class="LineNr">149 </span>    10:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> first list2
+<a name="L150"></a><span id="L150" class="LineNr">150 </span>    list2 <span class="Special">&lt;-</span> next list2
+<a name="L151"></a><span id="L151" class="LineNr">151 </span>    11:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> first list2
+<a name="L152"></a><span id="L152" class="LineNr">152 </span>    list2 <span class="Special">&lt;-</span> next list2
+<a name="L153"></a><span id="L153" class="LineNr">153 </span>    12:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> first list2
+<a name="L154"></a><span id="L154" class="LineNr">154 </span>    list2 <span class="Special">&lt;-</span> next list2
+<a name="L155"></a><span id="L155" class="LineNr">155 </span>    13:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> first list2
+<a name="L156"></a><span id="L156" class="LineNr">156 </span>    list2 <span class="Special">&lt;-</span> prev list2
+<a name="L157"></a><span id="L157" class="LineNr">157 </span>    20:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> first list2
+<a name="L158"></a><span id="L158" class="LineNr">158 </span>    list2 <span class="Special">&lt;-</span> prev list2
+<a name="L159"></a><span id="L159" class="LineNr">159 </span>    21:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> first list2
+<a name="L160"></a><span id="L160" class="LineNr">160 </span>    list2 <span class="Special">&lt;-</span> prev list2
+<a name="L161"></a><span id="L161" class="LineNr">161 </span>    22:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> first list2
+<a name="L162"></a><span id="L162" class="LineNr">162 </span>    30:bool/<span class="Special">raw</span> <span class="Special">&lt;-</span> equal list, list2
+<a name="L163"></a><span id="L163" class="LineNr">163 </span>  ]
+<a name="L164"></a><span id="L164" class="LineNr">164 </span>  memory-should-contain [
+<a name="L165"></a><span id="L165" class="LineNr">165 </span>   <span class="Constant"> 10</span> <span class="Special">&lt;-</span><span class="Constant"> 5</span>  <span class="Comment"># scanning next</span>
+<a name="L166"></a><span id="L166" class="LineNr">166 </span>   <span class="Constant"> 11</span> <span class="Special">&lt;-</span><span class="Constant"> 4</span>
+<a name="L167"></a><span id="L167" class="LineNr">167 </span>   <span class="Constant"> 12</span> <span class="Special">&lt;-</span><span class="Constant"> 3</span>
+<a name="L168"></a><span id="L168" class="LineNr">168 </span>   <span class="Constant"> 13</span> <span class="Special">&lt;-</span><span class="Constant"> 6</span>  <span class="Comment"># inserted element</span>
+<a name="L169"></a><span id="L169" class="LineNr">169 </span>   <span class="Constant"> 20</span> <span class="Special">&lt;-</span><span class="Constant"> 3</span>  <span class="Comment"># then prev</span>
+<a name="L170"></a><span id="L170" class="LineNr">170 </span>   <span class="Constant"> 21</span> <span class="Special">&lt;-</span><span class="Constant"> 4</span>
+<a name="L171"></a><span id="L171" class="LineNr">171 </span>   <span class="Constant"> 22</span> <span class="Special">&lt;-</span><span class="Constant"> 5</span>
+<a name="L172"></a><span id="L172" class="LineNr">172 </span>   <span class="Constant"> 30</span> <span class="Special">&lt;-</span><span class="Constant"> 1</span>  <span class="Comment"># list back at start</span>
+<a name="L173"></a><span id="L173" class="LineNr">173 </span>  ]
+<a name="L174"></a><span id="L174" class="LineNr">174 </span>]
+<a name="L175"></a><span id="L175" class="LineNr">175 </span>
+<a name="L176"></a><span id="L176" class="LineNr">176 </span><span class="muScenario">scenario</span> inserting-after-start-of-duplex-list [
+<a name="L177"></a><span id="L177" class="LineNr">177 </span>  <span class="Constant">local-scope</span>
+<a name="L178"></a><span id="L178" class="LineNr">178 </span>  list:&amp;:duplex-list:char <span class="Special">&lt;-</span> push<span class="Constant"> 3</span>,<span class="Constant"> 0</span>
+<a name="L179"></a><span id="L179" class="LineNr">179 </span>  list <span class="Special">&lt;-</span> push<span class="Constant"> 4</span>, list
+<a name="L180"></a><span id="L180" class="LineNr">180 </span>  list <span class="Special">&lt;-</span> push<span class="Constant"> 5</span>, list
+<a name="L181"></a><span id="L181" class="LineNr">181 </span>  run [
+<a name="L182"></a><span id="L182" class="LineNr">182 </span>    list <span class="Special">&lt;-</span> insert<span class="Constant"> 6</span>, list
+<a name="L183"></a><span id="L183" class="LineNr">183 </span>    <span class="Comment"># check structure like before</span>
+<a name="L184"></a><span id="L184" class="LineNr">184 </span>    list2:&amp;:duplex-list:char <span class="Special">&lt;-</span> copy list
+<a name="L185"></a><span id="L185" class="LineNr">185 </span>    10:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> first list2
+<a name="L186"></a><span id="L186" class="LineNr">186 </span>    list2 <span class="Special">&lt;-</span> next list2
+<a name="L187"></a><span id="L187" class="LineNr">187 </span>    11:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> first list2
+<a name="L188"></a><span id="L188" class="LineNr">188 </span>    list2 <span class="Special">&lt;-</span> next list2
+<a name="L189"></a><span id="L189" class="LineNr">189 </span>    12:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> first list2
+<a name="L190"></a><span id="L190" class="LineNr">190 </span>    list2 <span class="Special">&lt;-</span> next list2
+<a name="L191"></a><span id="L191" class="LineNr">191 </span>    13:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> first list2
+<a name="L192"></a><span id="L192" class="LineNr">192 </span>    list2 <span class="Special">&lt;-</span> prev list2
+<a name="L193"></a><span id="L193" class="LineNr">193 </span>    20:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> first list2
+<a name="L194"></a><span id="L194" class="LineNr">194 </span>    list2 <span class="Special">&lt;-</span> prev list2
+<a name="L195"></a><span id="L195" class="LineNr">195 </span>    21:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> first list2
+<a name="L196"></a><span id="L196" class="LineNr">196 </span>    list2 <span class="Special">&lt;-</span> prev list2
+<a name="L197"></a><span id="L197" class="LineNr">197 </span>    22:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> first list2
+<a name="L198"></a><span id="L198" class="LineNr">198 </span>    30:bool/<span class="Special">raw</span> <span class="Special">&lt;-</span> equal list, list2
+<a name="L199"></a><span id="L199" class="LineNr">199 </span>  ]
+<a name="L200"></a><span id="L200" class="LineNr">200 </span>  memory-should-contain [
+<a name="L201"></a><span id="L201" class="LineNr">201 </span>   <span class="Constant"> 10</span> <span class="Special">&lt;-</span><span class="Constant"> 5</span>  <span class="Comment"># scanning next</span>
+<a name="L202"></a><span id="L202" class="LineNr">202 </span>   <span class="Constant"> 11</span> <span class="Special">&lt;-</span><span class="Constant"> 6</span>  <span class="Comment"># inserted element</span>
+<a name="L203"></a><span id="L203" class="LineNr">203 </span>   <span class="Constant"> 12</span> <span class="Special">&lt;-</span><span class="Constant"> 4</span>
+<a name="L204"></a><span id="L204" class="LineNr">204 </span>   <span class="Constant"> 13</span> <span class="Special">&lt;-</span><span class="Constant"> 3</span>
+<a name="L205"></a><span id="L205" class="LineNr">205 </span>   <span class="Constant"> 20</span> <span class="Special">&lt;-</span><span class="Constant"> 4</span>  <span class="Comment"># then prev</span>
+<a name="L206"></a><span id="L206" class="LineNr">206 </span>   <span class="Constant"> 21</span> <span class="Special">&lt;-</span><span class="Constant"> 6</span>
+<a name="L207"></a><span id="L207" class="LineNr">207 </span>   <span class="Constant"> 22</span> <span class="Special">&lt;-</span><span class="Constant"> 5</span>
+<a name="L208"></a><span id="L208" class="LineNr">208 </span>   <span class="Constant"> 30</span> <span class="Special">&lt;-</span><span class="Constant"> 1</span>  <span class="Comment"># list back at start</span>
+<a name="L209"></a><span id="L209" class="LineNr">209 </span>  ]
+<a name="L210"></a><span id="L210" class="LineNr">210 </span>]
+<a name="L211"></a><span id="L211" class="LineNr">211 </span>
+<a name="L212"></a><span id="L212" class="LineNr">212 </span><span class="Comment"># remove 'x' from its surrounding list 'in'</span>
+<a name="L213"></a><span id="L213" class="LineNr">213 </span><span class="Comment">#</span>
+<a name="L214"></a><span id="L214" class="LineNr">214 </span><span class="Comment"># Returns null if and only if list is empty. Beware: in that case any other</span>
+<a name="L215"></a><span id="L215" class="LineNr">215 </span><span class="Comment"># pointers to the head are now invalid.</span>
+<a name="L216"></a><span id="L216" class="LineNr">216 </span><span class="muRecipe">def</span> remove x:&amp;:duplex-list:_elem/contained-in:in, in:&amp;:duplex-list:_elem<span class="muRecipe"> -&gt; </span>in:&amp;:duplex-list:_elem [
+<a name="L217"></a><span id="L217" class="LineNr">217 </span>  <span class="Constant">local-scope</span>
+<a name="L218"></a><span id="L218" class="LineNr">218 </span>  <span class="Constant">load-ingredients</span>
+<a name="L219"></a><span id="L219" class="LineNr">219 </span>  <span class="Comment"># if 'x' is null, return</span>
+<a name="L220"></a><span id="L220" class="LineNr">220 </span>  <span class="muControl">return-unless</span> x
+<a name="L221"></a><span id="L221" class="LineNr">221 </span>  next-node:&amp;:duplex-list:_elem <span class="Special">&lt;-</span> get *x, <span class="Constant">next:offset</span>
+<a name="L222"></a><span id="L222" class="LineNr">222 </span>  prev-node:&amp;:duplex-list:_elem <span class="Special">&lt;-</span> get *x, <span class="Constant">prev:offset</span>
+<a name="L223"></a><span id="L223" class="LineNr">223 </span>  <span class="Comment"># null x's pointers</span>
+<a name="L224"></a><span id="L224" class="LineNr">224 </span>  *x <span class="Special">&lt;-</span> put *x, <span class="Constant">next:offset</span>,<span class="Constant"> 0</span>
+<a name="L225"></a><span id="L225" class="LineNr">225 </span>  *x <span class="Special">&lt;-</span> put *x, <span class="Constant">prev:offset</span>,<span class="Constant"> 0</span>
+<a name="L226"></a><span id="L226" class="LineNr">226 </span>  <span class="Comment"># if next-node is not null, set its prev pointer</span>
+<a name="L227"></a><span id="L227" class="LineNr">227 </span>  <span class="Delimiter">{</span>
+<a name="L228"></a><span id="L228" class="LineNr">228 </span>    <span class="muControl">break-unless</span> next-node
+<a name="L229"></a><span id="L229" class="LineNr">229 </span>    *next-node <span class="Special">&lt;-</span> put *next-node, <span class="Constant">prev:offset</span>, prev-node
+<a name="L230"></a><span id="L230" class="LineNr">230 </span>  <span class="Delimiter">}</span>
+<a name="L231"></a><span id="L231" class="LineNr">231 </span>  <span class="Comment"># if prev-node is not null, set its next pointer and return</span>
+<a name="L232"></a><span id="L232" class="LineNr">232 </span>  <span class="Delimiter">{</span>
+<a name="L233"></a><span id="L233" class="LineNr">233 </span>    <span class="muControl">break-unless</span> prev-node
+<a name="L234"></a><span id="L234" class="LineNr">234 </span>    *prev-node <span class="Special">&lt;-</span> put *prev-node, <span class="Constant">next:offset</span>, next-node
+<a name="L235"></a><span id="L235" class="LineNr">235 </span>    <span class="muControl">return</span>
+<a name="L236"></a><span id="L236" class="LineNr">236 </span>  <span class="Delimiter">}</span>
+<a name="L237"></a><span id="L237" class="LineNr">237 </span>  <span class="Comment"># if prev-node is null, then we removed the head node at 'in'</span>
+<a name="L238"></a><span id="L238" class="LineNr">238 </span>  <span class="Comment"># return the new head rather than the old 'in'</span>
+<a name="L239"></a><span id="L239" class="LineNr">239 </span>  <span class="muControl">return</span> next-node
+<a name="L240"></a><span id="L240" class="LineNr">240 </span>]
+<a name="L241"></a><span id="L241" class="LineNr">241 </span>
+<a name="L242"></a><span id="L242" class="LineNr">242 </span><span class="muScenario">scenario</span> removing-from-duplex-list [
+<a name="L243"></a><span id="L243" class="LineNr">243 </span>  <span class="Constant">local-scope</span>
+<a name="L244"></a><span id="L244" class="LineNr">244 </span>  list:&amp;:duplex-list:char <span class="Special">&lt;-</span> push<span class="Constant"> 3</span>,<span class="Constant"> 0</span>
+<a name="L245"></a><span id="L245" class="LineNr">245 </span>  list <span class="Special">&lt;-</span> push<span class="Constant"> 4</span>, list
+<a name="L246"></a><span id="L246" class="LineNr">246 </span>  list <span class="Special">&lt;-</span> push<span class="Constant"> 5</span>, list
+<a name="L247"></a><span id="L247" class="LineNr">247 </span>  run [
+<a name="L248"></a><span id="L248" class="LineNr">248 </span>    list2:&amp;:duplex-list:char <span class="Special">&lt;-</span> next list  <span class="Comment"># second element</span>
+<a name="L249"></a><span id="L249" class="LineNr">249 </span>    list <span class="Special">&lt;-</span> remove list2, list
+<a name="L250"></a><span id="L250" class="LineNr">250 </span>    10:bool/<span class="Special">raw</span> <span class="Special">&lt;-</span> equal list2,<span class="Constant"> 0</span>
+<a name="L251"></a><span id="L251" class="LineNr">251 </span>    <span class="Comment"># check structure like before</span>
+<a name="L252"></a><span id="L252" class="LineNr">252 </span>    list2 <span class="Special">&lt;-</span> copy list
+<a name="L253"></a><span id="L253" class="LineNr">253 </span>    11:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> first list2
+<a name="L254"></a><span id="L254" class="LineNr">254 </span>    list2 <span class="Special">&lt;-</span> next list2
+<a name="L255"></a><span id="L255" class="LineNr">255 </span>    12:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> first list2
+<a name="L256"></a><span id="L256" class="LineNr">256 </span>    20:&amp;:duplex-list:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> next list2
+<a name="L257"></a><span id="L257" class="LineNr">257 </span>    list2 <span class="Special">&lt;-</span> prev list2
+<a name="L258"></a><span id="L258" class="LineNr">258 </span>    30:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> first list2
+<a name="L259"></a><span id="L259" class="LineNr">259 </span>    40:bool/<span class="Special">raw</span> <span class="Special">&lt;-</span> equal list, list2
+<a name="L260"></a><span id="L260" class="LineNr">260 </span>  ]
+<a name="L261"></a><span id="L261" class="LineNr">261 </span>  memory-should-contain [
+<a name="L262"></a><span id="L262" class="LineNr">262 </span>   <span class="Constant"> 10</span> <span class="Special">&lt;-</span><span class="Constant"> 0</span>  <span class="Comment"># remove returned non-null</span>
+<a name="L263"></a><span id="L263" class="LineNr">263 </span>   <span class="Constant"> 11</span> <span class="Special">&lt;-</span><span class="Constant"> 5</span>  <span class="Comment"># scanning next, skipping deleted element</span>
+<a name="L264"></a><span id="L264" class="LineNr">264 </span>   <span class="Constant"> 12</span> <span class="Special">&lt;-</span><span class="Constant"> 3</span>
+<a name="L265"></a><span id="L265" class="LineNr">265 </span>   <span class="Constant"> 20</span> <span class="Special">&lt;-</span><span class="Constant"> 0</span>  <span class="Comment"># no more elements</span>
+<a name="L266"></a><span id="L266" class="LineNr">266 </span>   <span class="Constant"> 30</span> <span class="Special">&lt;-</span><span class="Constant"> 5</span>  <span class="Comment"># prev of final element</span>
+<a name="L267"></a><span id="L267" class="LineNr">267 </span>   <span class="Constant"> 40</span> <span class="Special">&lt;-</span><span class="Constant"> 1</span>  <span class="Comment"># list back at start</span>
+<a name="L268"></a><span id="L268" class="LineNr">268 </span>  ]
+<a name="L269"></a><span id="L269" class="LineNr">269 </span>]
+<a name="L270"></a><span id="L270" class="LineNr">270 </span>
+<a name="L271"></a><span id="L271" class="LineNr">271 </span><span class="muScenario">scenario</span> removing-from-start-of-duplex-list [
+<a name="L272"></a><span id="L272" class="LineNr">272 </span>  <span class="Constant">local-scope</span>
+<a name="L273"></a><span id="L273" class="LineNr">273 </span>  list:&amp;:duplex-list:char <span class="Special">&lt;-</span> push<span class="Constant"> 3</span>,<span class="Constant"> 0</span>
+<a name="L274"></a><span id="L274" class="LineNr">274 </span>  list <span class="Special">&lt;-</span> push<span class="Constant"> 4</span>, list
+<a name="L275"></a><span id="L275" class="LineNr">275 </span>  list <span class="Special">&lt;-</span> push<span class="Constant"> 5</span>, list
+<a name="L276"></a><span id="L276" class="LineNr">276 </span>  run [
+<a name="L277"></a><span id="L277" class="LineNr">277 </span>    list <span class="Special">&lt;-</span> remove list, list
+<a name="L278"></a><span id="L278" class="LineNr">278 </span>    <span class="Comment"># check structure like before</span>
+<a name="L279"></a><span id="L279" class="LineNr">279 </span>    list2:&amp;:duplex-list:char <span class="Special">&lt;-</span> copy list
+<a name="L280"></a><span id="L280" class="LineNr">280 </span>    10:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> first list2
+<a name="L281"></a><span id="L281" class="LineNr">281 </span>    list2 <span class="Special">&lt;-</span> next list2
+<a name="L282"></a><span id="L282" class="LineNr">282 </span>    11:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> first list2
+<a name="L283"></a><span id="L283" class="LineNr">283 </span>    20:&amp;:duplex-list:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> next list2
+<a name="L284"></a><span id="L284" class="LineNr">284 </span>    list2 <span class="Special">&lt;-</span> prev list2
+<a name="L285"></a><span id="L285" class="LineNr">285 </span>    30:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> first list2
+<a name="L286"></a><span id="L286" class="LineNr">286 </span>    40:bool/<span class="Special">raw</span> <span class="Special">&lt;-</span> equal list, list2
+<a name="L287"></a><span id="L287" class="LineNr">287 </span>  ]
+<a name="L288"></a><span id="L288" class="LineNr">288 </span>  memory-should-contain [
+<a name="L289"></a><span id="L289" class="LineNr">289 </span>   <span class="Constant"> 10</span> <span class="Special">&lt;-</span><span class="Constant"> 4</span>  <span class="Comment"># scanning next, skipping deleted element</span>
+<a name="L290"></a><span id="L290" class="LineNr">290 </span>   <span class="Constant"> 11</span> <span class="Special">&lt;-</span><span class="Constant"> 3</span>
+<a name="L291"></a><span id="L291" class="LineNr">291 </span>   <span class="Constant"> 20</span> <span class="Special">&lt;-</span><span class="Constant"> 0</span>  <span class="Comment"># no more elements</span>
+<a name="L292"></a><span id="L292" class="LineNr">292 </span>   <span class="Constant"> 30</span> <span class="Special">&lt;-</span><span class="Constant"> 4</span>  <span class="Comment"># prev of final element</span>
+<a name="L293"></a><span id="L293" class="LineNr">293 </span>   <span class="Constant"> 40</span> <span class="Special">&lt;-</span><span class="Constant"> 1</span>  <span class="Comment"># list back at start</span>
+<a name="L294"></a><span id="L294" class="LineNr">294 </span>  ]
+<a name="L295"></a><span id="L295" class="LineNr">295 </span>]
+<a name="L296"></a><span id="L296" class="LineNr">296 </span>
+<a name="L297"></a><span id="L297" class="LineNr">297 </span><span class="muScenario">scenario</span> removing-from-end-of-duplex-list [
+<a name="L298"></a><span id="L298" class="LineNr">298 </span>  <span class="Constant">local-scope</span>
+<a name="L299"></a><span id="L299" class="LineNr">299 </span>  list:&amp;:duplex-list:char <span class="Special">&lt;-</span> push<span class="Constant"> 3</span>,<span class="Constant"> 0</span>
+<a name="L300"></a><span id="L300" class="LineNr">300 </span>  list <span class="Special">&lt;-</span> push<span class="Constant"> 4</span>, list
+<a name="L301"></a><span id="L301" class="LineNr">301 </span>  list <span class="Special">&lt;-</span> push<span class="Constant"> 5</span>, list
+<a name="L302"></a><span id="L302" class="LineNr">302 </span>  run [
+<a name="L303"></a><span id="L303" class="LineNr">303 </span>    <span class="Comment"># delete last element</span>
+<a name="L304"></a><span id="L304" class="LineNr">304 </span>    list2:&amp;:duplex-list:char <span class="Special">&lt;-</span> next list
+<a name="L305"></a><span id="L305" class="LineNr">305 </span>    list2 <span class="Special">&lt;-</span> next list2
+<a name="L306"></a><span id="L306" class="LineNr">306 </span>    list <span class="Special">&lt;-</span> remove list2, list
+<a name="L307"></a><span id="L307" class="LineNr">307 </span>    10:bool/<span class="Special">raw</span> <span class="Special">&lt;-</span> equal list2,<span class="Constant"> 0</span>
+<a name="L308"></a><span id="L308" class="LineNr">308 </span>    <span class="Comment"># check structure like before</span>
+<a name="L309"></a><span id="L309" class="LineNr">309 </span>    list2 <span class="Special">&lt;-</span> copy list
+<a name="L310"></a><span id="L310" class="LineNr">310 </span>    11:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> first list2
+<a name="L311"></a><span id="L311" class="LineNr">311 </span>    list2 <span class="Special">&lt;-</span> next list2
+<a name="L312"></a><span id="L312" class="LineNr">312 </span>    12:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> first list2
+<a name="L313"></a><span id="L313" class="LineNr">313 </span>    20:&amp;:duplex-list:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> next list2
+<a name="L314"></a><span id="L314" class="LineNr">314 </span>    list2 <span class="Special">&lt;-</span> prev list2
+<a name="L315"></a><span id="L315" class="LineNr">315 </span>    30:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> first list2
+<a name="L316"></a><span id="L316" class="LineNr">316 </span>    40:bool/<span class="Special">raw</span> <span class="Special">&lt;-</span> equal list, list2
+<a name="L317"></a><span id="L317" class="LineNr">317 </span>  ]
+<a name="L318"></a><span id="L318" class="LineNr">318 </span>  memory-should-contain [
+<a name="L319"></a><span id="L319" class="LineNr">319 </span>   <span class="Constant"> 10</span> <span class="Special">&lt;-</span><span class="Constant"> 0</span>  <span class="Comment"># remove returned non-null</span>
+<a name="L320"></a><span id="L320" class="LineNr">320 </span>   <span class="Constant"> 11</span> <span class="Special">&lt;-</span><span class="Constant"> 5</span>  <span class="Comment"># scanning next, skipping deleted element</span>
+<a name="L321"></a><span id="L321" class="LineNr">321 </span>   <span class="Constant"> 12</span> <span class="Special">&lt;-</span><span class="Constant"> 4</span>
+<a name="L322"></a><span id="L322" class="LineNr">322 </span>   <span class="Constant"> 20</span> <span class="Special">&lt;-</span><span class="Constant"> 0</span>  <span class="Comment"># no more elements</span>
+<a name="L323"></a><span id="L323" class="LineNr">323 </span>   <span class="Constant"> 30</span> <span class="Special">&lt;-</span><span class="Constant"> 5</span>  <span class="Comment"># prev of final element</span>
+<a name="L324"></a><span id="L324" class="LineNr">324 </span>   <span class="Constant"> 40</span> <span class="Special">&lt;-</span><span class="Constant"> 1</span>  <span class="Comment"># list back at start</span>
+<a name="L325"></a><span id="L325" class="LineNr">325 </span>  ]
+<a name="L326"></a><span id="L326" class="LineNr">326 </span>]
+<a name="L327"></a><span id="L327" class="LineNr">327 </span>
+<a name="L328"></a><span id="L328" class="LineNr">328 </span><span class="muScenario">scenario</span> removing-from-singleton-duplex-list [
+<a name="L329"></a><span id="L329" class="LineNr">329 </span>  <span class="Constant">local-scope</span>
+<a name="L330"></a><span id="L330" class="LineNr">330 </span>  list:&amp;:duplex-list:char <span class="Special">&lt;-</span> push<span class="Constant"> 3</span>,<span class="Constant"> 0</span>
+<a name="L331"></a><span id="L331" class="LineNr">331 </span>  run [
+<a name="L332"></a><span id="L332" class="LineNr">332 </span>    list <span class="Special">&lt;-</span> remove list, list
+<a name="L333"></a><span id="L333" class="LineNr">333 </span>    1:num/<span class="Special">raw</span> <span class="Special">&lt;-</span> copy list
+<a name="L334"></a><span id="L334" class="LineNr">334 </span>  ]
+<a name="L335"></a><span id="L335" class="LineNr">335 </span>  memory-should-contain [
+<a name="L336"></a><span id="L336" class="LineNr">336 </span>   <span class="Constant"> 1</span> <span class="Special">&lt;-</span><span class="Constant"> 0</span>  <span class="Comment"># back to an empty list</span>
+<a name="L337"></a><span id="L337" class="LineNr">337 </span>  ]
+<a name="L338"></a><span id="L338" class="LineNr">338 </span>]
+<a name="L339"></a><span id="L339" class="LineNr">339 </span>
+<a name="L340"></a><span id="L340" class="LineNr">340 </span><span class="Comment"># remove values between 'start' and 'end' (both exclusive).</span>
+<a name="L341"></a><span id="L341" class="LineNr">341 </span><span class="Comment"># also clear pointers back out from start/end for hygiene.</span>
+<a name="L342"></a><span id="L342" class="LineNr">342 </span><span class="Comment"># set end to 0 to delete everything past start.</span>
+<a name="L343"></a><span id="L343" class="LineNr">343 </span><span class="Comment"># can't set start to 0 to delete everything before end, because there's no</span>
+<a name="L344"></a><span id="L344" class="LineNr">344 </span><span class="Comment"># clean way to return the new head pointer.</span>
+<a name="L345"></a><span id="L345" class="LineNr">345 </span><span class="muRecipe">def</span> remove-between start:&amp;:duplex-list:_elem, end:&amp;:duplex-list:_elem/contained-in:start<span class="muRecipe"> -&gt; </span>start:&amp;:duplex-list:_elem [
+<a name="L346"></a><span id="L346" class="LineNr">346 </span>  <span class="Constant">local-scope</span>
+<a name="L347"></a><span id="L347" class="LineNr">347 </span>  <span class="Constant">load-ingredients</span>
+<a name="L348"></a><span id="L348" class="LineNr">348 </span>  next:&amp;:duplex-list:_elem <span class="Special">&lt;-</span> get *start, <span class="Constant">next:offset</span>
+<a name="L349"></a><span id="L349" class="LineNr">349 </span>  nothing-to-delete?:bool <span class="Special">&lt;-</span> equal next, end
+<a name="L350"></a><span id="L350" class="LineNr">350 </span>  <span class="muControl">return-if</span> nothing-to-delete?
+<a name="L351"></a><span id="L351" class="LineNr">351 </span>  assert next, <span class="Constant">[malformed duplex list]</span>
+<a name="L352"></a><span id="L352" class="LineNr">352 </span>  <span class="Comment"># start-&gt;next-&gt;prev = 0</span>
+<a name="L353"></a><span id="L353" class="LineNr">353 </span>  <span class="Comment"># start-&gt;next = end</span>
+<a name="L354"></a><span id="L354" class="LineNr">354 </span>  *next <span class="Special">&lt;-</span> put *next, <span class="Constant">prev:offset</span>,<span class="Constant"> 0</span>
+<a name="L355"></a><span id="L355" class="LineNr">355 </span>  *start <span class="Special">&lt;-</span> put *start, <span class="Constant">next:offset</span>, end
+<a name="L356"></a><span id="L356" class="LineNr">356 </span>  <span class="muControl">return-unless</span> end
+<a name="L357"></a><span id="L357" class="LineNr">357 </span>  <span class="Comment"># end-&gt;prev-&gt;next = 0</span>
+<a name="L358"></a><span id="L358" class="LineNr">358 </span>  <span class="Comment"># end-&gt;prev = start</span>
+<a name="L359"></a><span id="L359" class="LineNr">359 </span>  prev:&amp;:duplex-list:_elem <span class="Special">&lt;-</span> get *end, <span class="Constant">prev:offset</span>
+<a name="L360"></a><span id="L360" class="LineNr">360 </span>  assert prev, <span class="Constant">[malformed duplex list - 2]</span>
+<a name="L361"></a><span id="L361" class="LineNr">361 </span>  *prev <span class="Special">&lt;-</span> put *prev, <span class="Constant">next:offset</span>,<span class="Constant"> 0</span>
+<a name="L362"></a><span id="L362" class="LineNr">362 </span>  *end <span class="Special">&lt;-</span> put *end, <span class="Constant">prev:offset</span>, start
+<a name="L363"></a><span id="L363" class="LineNr">363 </span>]
+<a name="L364"></a><span id="L364" class="LineNr">364 </span>
+<a name="L365"></a><span id="L365" class="LineNr">365 </span><span class="muScenario">scenario</span> remove-range [
+<a name="L366"></a><span id="L366" class="LineNr">366 </span>  <span class="Comment"># construct a duplex list with six elements [13, 14, 15, 16, 17, 18]</span>
+<a name="L367"></a><span id="L367" class="LineNr">367 </span>  <span class="Constant">local-scope</span>
+<a name="L368"></a><span id="L368" class="LineNr">368 </span>  list:&amp;:duplex-list:char <span class="Special">&lt;-</span> push<span class="Constant"> 18</span>,<span class="Constant"> 0</span>
+<a name="L369"></a><span id="L369" class="LineNr">369 </span>  list <span class="Special">&lt;-</span> push<span class="Constant"> 17</span>, list
+<a name="L370"></a><span id="L370" class="LineNr">370 </span>  list <span class="Special">&lt;-</span> push<span class="Constant"> 16</span>, list
+<a name="L371"></a><span id="L371" class="LineNr">371 </span>  list <span class="Special">&lt;-</span> push<span class="Constant"> 15</span>, list
+<a name="L372"></a><span id="L372" class="LineNr">372 </span>  list <span class="Special">&lt;-</span> push<span class="Constant"> 14</span>, list
+<a name="L373"></a><span id="L373" class="LineNr">373 </span>  list <span class="Special">&lt;-</span> push<span class="Constant"> 13</span>, list
+<a name="L374"></a><span id="L374" class="LineNr">374 </span>  run [
+<a name="L375"></a><span id="L375" class="LineNr">375 </span>    <span class="Comment"># delete 16 onwards</span>
+<a name="L376"></a><span id="L376" class="LineNr">376 </span>    <span class="Comment"># first pointer: to the third element</span>
+<a name="L377"></a><span id="L377" class="LineNr">377 </span>    list2:&amp;:duplex-list:char <span class="Special">&lt;-</span> next list
+<a name="L378"></a><span id="L378" class="LineNr">378 </span>    list2 <span class="Special">&lt;-</span> next list2
+<a name="L379"></a><span id="L379" class="LineNr">379 </span>    list2 <span class="Special">&lt;-</span> remove-between list2,<span class="Constant"> 0</span>
+<a name="L380"></a><span id="L380" class="LineNr">380 </span>    <span class="Comment"># now check the list</span>
+<a name="L381"></a><span id="L381" class="LineNr">381 </span>    10:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> get *list, <span class="Constant">value:offset</span>
+<a name="L382"></a><span id="L382" class="LineNr">382 </span>    list <span class="Special">&lt;-</span> next list
+<a name="L383"></a><span id="L383" class="LineNr">383 </span>    11:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> get *list, <span class="Constant">value:offset</span>
+<a name="L384"></a><span id="L384" class="LineNr">384 </span>    list <span class="Special">&lt;-</span> next list
+<a name="L385"></a><span id="L385" class="LineNr">385 </span>    12:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> get *list, <span class="Constant">value:offset</span>
+<a name="L386"></a><span id="L386" class="LineNr">386 </span>    20:&amp;:duplex-list:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> next list
+<a name="L387"></a><span id="L387" class="LineNr">387 </span>  ]
+<a name="L388"></a><span id="L388" class="LineNr">388 </span>  memory-should-contain [
+<a name="L389"></a><span id="L389" class="LineNr">389 </span>   <span class="Constant"> 10</span> <span class="Special">&lt;-</span><span class="Constant"> 13</span>
+<a name="L390"></a><span id="L390" class="LineNr">390 </span>   <span class="Constant"> 11</span> <span class="Special">&lt;-</span><span class="Constant"> 14</span>
+<a name="L391"></a><span id="L391" class="LineNr">391 </span>   <span class="Constant"> 12</span> <span class="Special">&lt;-</span><span class="Constant"> 15</span>
+<a name="L392"></a><span id="L392" class="LineNr">392 </span>   <span class="Constant"> 20</span> <span class="Special">&lt;-</span><span class="Constant"> 0</span>
+<a name="L393"></a><span id="L393" class="LineNr">393 </span>  ]
+<a name="L394"></a><span id="L394" class="LineNr">394 </span>]
+<a name="L395"></a><span id="L395" class="LineNr">395 </span>
+<a name="L396"></a><span id="L396" class="LineNr">396 </span><span class="muScenario">scenario</span> remove-range-to-final [
+<a name="L397"></a><span id="L397" class="LineNr">397 </span>  <span class="Constant">local-scope</span>
+<a name="L398"></a><span id="L398" class="LineNr">398 </span>  <span class="Comment"># construct a duplex list with six elements [13, 14, 15, 16, 17, 18]</span>
+<a name="L399"></a><span id="L399" class="LineNr">399 </span>  list:&amp;:duplex-list:char <span class="Special">&lt;-</span> push<span class="Constant"> 18</span>,<span class="Constant"> 0</span>
+<a name="L400"></a><span id="L400" class="LineNr">400 </span>  list <span class="Special">&lt;-</span> push<span class="Constant"> 17</span>, list
+<a name="L401"></a><span id="L401" class="LineNr">401 </span>  list <span class="Special">&lt;-</span> push<span class="Constant"> 16</span>, list
+<a name="L402"></a><span id="L402" class="LineNr">402 </span>  list <span class="Special">&lt;-</span> push<span class="Constant"> 15</span>, list
+<a name="L403"></a><span id="L403" class="LineNr">403 </span>  list <span class="Special">&lt;-</span> push<span class="Constant"> 14</span>, list
+<a name="L404"></a><span id="L404" class="LineNr">404 </span>  list <span class="Special">&lt;-</span> push<span class="Constant"> 13</span>, list
+<a name="L405"></a><span id="L405" class="LineNr">405 </span>  run [
+<a name="L406"></a><span id="L406" class="LineNr">406 </span>    <span class="Comment"># delete 15, 16 and 17</span>
+<a name="L407"></a><span id="L407" class="LineNr">407 </span>    <span class="Comment"># start pointer: to the second element</span>
+<a name="L408"></a><span id="L408" class="LineNr">408 </span>    list2:&amp;:duplex-list:char <span class="Special">&lt;-</span> next list
+<a name="L409"></a><span id="L409" class="LineNr">409 </span>    <span class="Comment"># end pointer: to the last (sixth) element</span>
+<a name="L410"></a><span id="L410" class="LineNr">410 </span>    end:&amp;:duplex-list:char <span class="Special">&lt;-</span> next list2
+<a name="L411"></a><span id="L411" class="LineNr">411 </span>    end <span class="Special">&lt;-</span> next end
+<a name="L412"></a><span id="L412" class="LineNr">412 </span>    end <span class="Special">&lt;-</span> next end
+<a name="L413"></a><span id="L413" class="LineNr">413 </span>    end <span class="Special">&lt;-</span> next end
+<a name="L414"></a><span id="L414" class="LineNr">414 </span>    remove-between list2, end
+<a name="L415"></a><span id="L415" class="LineNr">415 </span>    <span class="Comment"># now check the list</span>
+<a name="L416"></a><span id="L416" class="LineNr">416 </span>    10:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> get *list, <span class="Constant">value:offset</span>
+<a name="L417"></a><span id="L417" class="LineNr">417 </span>    list <span class="Special">&lt;-</span> next list
+<a name="L418"></a><span id="L418" class="LineNr">418 </span>    11:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> get *list, <span class="Constant">value:offset</span>
+<a name="L419"></a><span id="L419" class="LineNr">419 </span>    list <span class="Special">&lt;-</span> next list
+<a name="L420"></a><span id="L420" class="LineNr">420 </span>    12:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> get *list, <span class="Constant">value:offset</span>
+<a name="L421"></a><span id="L421" class="LineNr">421 </span>    20:&amp;:duplex-list:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> next list
+<a name="L422"></a><span id="L422" class="LineNr">422 </span>  ]
+<a name="L423"></a><span id="L423" class="LineNr">423 </span>  memory-should-contain [
+<a name="L424"></a><span id="L424" class="LineNr">424 </span>   <span class="Constant"> 10</span> <span class="Special">&lt;-</span><span class="Constant"> 13</span>
+<a name="L425"></a><span id="L425" class="LineNr">425 </span>   <span class="Constant"> 11</span> <span class="Special">&lt;-</span><span class="Constant"> 14</span>
+<a name="L426"></a><span id="L426" class="LineNr">426 </span>   <span class="Constant"> 12</span> <span class="Special">&lt;-</span><span class="Constant"> 18</span>
+<a name="L427"></a><span id="L427" class="LineNr">427 </span>   <span class="Constant"> 20</span> <span class="Special">&lt;-</span><span class="Constant"> 0</span>  <span class="Comment"># no more elements</span>
+<a name="L428"></a><span id="L428" class="LineNr">428 </span>  ]
+<a name="L429"></a><span id="L429" class="LineNr">429 </span>]
+<a name="L430"></a><span id="L430" class="LineNr">430 </span>
+<a name="L431"></a><span id="L431" class="LineNr">431 </span><span class="muScenario">scenario</span> remove-range-empty [
+<a name="L432"></a><span id="L432" class="LineNr">432 </span>  <span class="Constant">local-scope</span>
+<a name="L433"></a><span id="L433" class="LineNr">433 </span>  <span class="Comment"># construct a duplex list with three elements [13, 14, 15]</span>
+<a name="L434"></a><span id="L434" class="LineNr">434 </span>  list:&amp;:duplex-list:char <span class="Special">&lt;-</span> push<span class="Constant"> 15</span>,<span class="Constant"> 0</span>
+<a name="L435"></a><span id="L435" class="LineNr">435 </span>  list <span class="Special">&lt;-</span> push<span class="Constant"> 14</span>, list
+<a name="L436"></a><span id="L436" class="LineNr">436 </span>  list <span class="Special">&lt;-</span> push<span class="Constant"> 13</span>, list
+<a name="L437"></a><span id="L437" class="LineNr">437 </span>  run [
+<a name="L438"></a><span id="L438" class="LineNr">438 </span>    <span class="Comment"># delete between first and second element (i.e. nothing)</span>
+<a name="L439"></a><span id="L439" class="LineNr">439 </span>    list2:&amp;:duplex-list:char <span class="Special">&lt;-</span> next list
+<a name="L440"></a><span id="L440" class="LineNr">440 </span>    remove-between list, list2
+<a name="L441"></a><span id="L441" class="LineNr">441 </span>    <span class="Comment"># now check the list</span>
+<a name="L442"></a><span id="L442" class="LineNr">442 </span>    10:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> get *list, <span class="Constant">value:offset</span>
+<a name="L443"></a><span id="L443" class="LineNr">443 </span>    list <span class="Special">&lt;-</span> next list
+<a name="L444"></a><span id="L444" class="LineNr">444 </span>    11:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> get *list, <span class="Constant">value:offset</span>
+<a name="L445"></a><span id="L445" class="LineNr">445 </span>    list <span class="Special">&lt;-</span> next list
+<a name="L446"></a><span id="L446" class="LineNr">446 </span>    12:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> get *list, <span class="Constant">value:offset</span>
+<a name="L447"></a><span id="L447" class="LineNr">447 </span>    20:&amp;:duplex-list:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> next list
+<a name="L448"></a><span id="L448" class="LineNr">448 </span>  ]
+<a name="L449"></a><span id="L449" class="LineNr">449 </span>  <span class="Comment"># no change</span>
+<a name="L450"></a><span id="L450" class="LineNr">450 </span>  memory-should-contain [
+<a name="L451"></a><span id="L451" class="LineNr">451 </span>   <span class="Constant"> 10</span> <span class="Special">&lt;-</span><span class="Constant"> 13</span>
+<a name="L452"></a><span id="L452" class="LineNr">452 </span>   <span class="Constant"> 11</span> <span class="Special">&lt;-</span><span class="Constant"> 14</span>
+<a name="L453"></a><span id="L453" class="LineNr">453 </span>   <span class="Constant"> 12</span> <span class="Special">&lt;-</span><span class="Constant"> 15</span>
+<a name="L454"></a><span id="L454" class="LineNr">454 </span>   <span class="Constant"> 20</span> <span class="Special">&lt;-</span><span class="Constant"> 0</span>
+<a name="L455"></a><span id="L455" class="LineNr">455 </span>  ]
+<a name="L456"></a><span id="L456" class="LineNr">456 </span>]
+<a name="L457"></a><span id="L457" class="LineNr">457 </span>
+<a name="L458"></a><span id="L458" class="LineNr">458 </span><span class="muScenario">scenario</span> remove-range-to-end [
+<a name="L459"></a><span id="L459" class="LineNr">459 </span>  <span class="Constant">local-scope</span>
+<a name="L460"></a><span id="L460" class="LineNr">460 </span>  <span class="Comment"># construct a duplex list with six elements [13, 14, 15, 16, 17, 18]</span>
+<a name="L461"></a><span id="L461" class="LineNr">461 </span>  list:&amp;:duplex-list:char <span class="Special">&lt;-</span> push<span class="Constant"> 18</span>,<span class="Constant"> 0</span>
+<a name="L462"></a><span id="L462" class="LineNr">462 </span>  list <span class="Special">&lt;-</span> push<span class="Constant"> 17</span>, list
+<a name="L463"></a><span id="L463" class="LineNr">463 </span>  list <span class="Special">&lt;-</span> push<span class="Constant"> 16</span>, list
+<a name="L464"></a><span id="L464" class="LineNr">464 </span>  list <span class="Special">&lt;-</span> push<span class="Constant"> 15</span>, list
+<a name="L465"></a><span id="L465" class="LineNr">465 </span>  list <span class="Special">&lt;-</span> push<span class="Constant"> 14</span>, list
+<a name="L466"></a><span id="L466" class="LineNr">466 </span>  list <span class="Special">&lt;-</span> push<span class="Constant"> 13</span>, list
+<a name="L467"></a><span id="L467" class="LineNr">467 </span>  run [
+<a name="L468"></a><span id="L468" class="LineNr">468 </span>    <span class="Comment"># remove the third element and beyond</span>
+<a name="L469"></a><span id="L469" class="LineNr">469 </span>    list2:&amp;:duplex-list:char <span class="Special">&lt;-</span> next list
+<a name="L470"></a><span id="L470" class="LineNr">470 </span>    remove-between list2,<span class="Constant"> 0</span>
+<a name="L471"></a><span id="L471" class="LineNr">471 </span>    <span class="Comment"># now check the list</span>
+<a name="L472"></a><span id="L472" class="LineNr">472 </span>    10:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> get *list, <span class="Constant">value:offset</span>
+<a name="L473"></a><span id="L473" class="LineNr">473 </span>    list <span class="Special">&lt;-</span> next list
+<a name="L474"></a><span id="L474" class="LineNr">474 </span>    11:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> get *list, <span class="Constant">value:offset</span>
+<a name="L475"></a><span id="L475" class="LineNr">475 </span>    20:&amp;:duplex-list:char/<span class="Special">raw</span> <span class="Special">&lt;-</span> next list
+<a name="L476"></a><span id="L476" class="LineNr">476 </span>  ]
+<a name="L477"></a><span id="L477" class="LineNr">477 </span>  memory-should-contain [
+<a name="L478"></a><span id="L478" class="LineNr">478 </span>   <span class="Constant"> 10</span> <span class="Special">&lt;-</span><span class="Constant"> 13</span>
+<a name="L479"></a><span id="L479" class="LineNr">479 </span>   <span class="Constant"> 11</span> <span class="Special">&lt;-</span><span class="Constant"> 14</span>
+<a name="L480"></a><span id="L480" class="LineNr">480 </span>   <span class="Constant"> 20</span> <span class="Special">&lt;-</span><span class="Constant"> 0</span>
+<a name="L481"></a><span id="L481" class="LineNr">481 </span>  ]
+<a name="L482"></a><span id="L482" class="LineNr">482 </span>]
+<a name="L483"></a><span id="L483" class="LineNr">483 </span>
+<a name="L484"></a><span id="L484" class="LineNr">484 </span><span class="Comment"># insert list beginning at 'new' after 'in'</span>
+<a name="L485"></a><span id="L485" class="LineNr">485 </span><span class="muRecipe">def</span> insert-range in:&amp;:duplex-list:_elem, start:&amp;:duplex-list:_elem/contained-in:in<span class="muRecipe"> -&gt; </span>in:&amp;:duplex-list:_elem [
+<a name="L486"></a><span id="L486" class="LineNr">486 </span>  <span class="Constant">local-scope</span>
+<a name="L487"></a><span id="L487" class="LineNr">487 </span>  <span class="Constant">load-ingredients</span>
+<a name="L488"></a><span id="L488" class="LineNr">488 </span>  <span class="muControl">return-unless</span> in
+<a name="L489"></a><span id="L489" class="LineNr">489 </span>  <span class="muControl">return-unless</span> start
+<a name="L490"></a><span id="L490" class="LineNr">490 </span>  end:&amp;:duplex-list:_elem <span class="Special">&lt;-</span> copy start
+<a name="L491"></a><span id="L491" class="LineNr">491 </span>  <span class="Delimiter">{</span>
+<a name="L492"></a><span id="L492" class="LineNr">492 </span>    next:&amp;:duplex-list:_elem <span class="Special">&lt;-</span> next end/insert-range
+<a name="L493"></a><span id="L493" class="LineNr">493 </span>    <span class="muControl">break-unless</span> next
+<a name="L494"></a><span id="L494" class="LineNr">494 </span>    end <span class="Special">&lt;-</span> copy next
+<a name="L495"></a><span id="L495" class="LineNr">495 </span>    <span class="muControl">loop</span>
+<a name="L496"></a><span id="L496" class="LineNr">496 </span>  <span class="Delimiter">}</span>
+<a name="L497"></a><span id="L497" class="LineNr">497 </span>  next:&amp;:duplex-list:_elem <span class="Special">&lt;-</span> next in
+<a name="L498"></a><span id="L498" class="LineNr">498 </span>  *end <span class="Special">&lt;-</span> put *end, <span class="Constant">next:offset</span>, next
+<a name="L499"></a><span id="L499" class="LineNr">499 </span>  <span class="Delimiter">{</span>
+<a name="L500"></a><span id="L500" class="LineNr">500 </span>    <span class="muControl">break-unless</span> next
+<a name="L501"></a><span id="L501" class="LineNr">501 </span>    *next <span class="Special">&lt;-</span> put *next, <span class="Constant">prev:offset</span>, end
+<a name="L502"></a><span id="L502" class="LineNr">502 </span>  <span class="Delimiter">}</span>
+<a name="L503"></a><span id="L503" class="LineNr">503 </span>  *in <span class="Special">&lt;-</span> put *in, <span class="Constant">next:offset</span>, start
+<a name="L504"></a><span id="L504" class="LineNr">504 </span>  *start <span class="Special">&lt;-</span> put *start, <span class="Constant">prev:offset</span>, in
+<a name="L505"></a><span id="L505" class="LineNr">505 </span>]
+<a name="L506"></a><span id="L506" class="LineNr">506 </span>
+<a name="L507"></a><span id="L507" class="LineNr">507 </span><span class="muRecipe">def</span> append in:&amp;:duplex-list:_elem, new:&amp;:duplex-list:_elem/contained-in:in<span class="muRecipe"> -&gt; </span>in:&amp;:duplex-list:_elem [
+<a name="L508"></a><span id="L508" class="LineNr">508 </span>  <span class="Constant">local-scope</span>
+<a name="L509"></a><span id="L509" class="LineNr">509 </span>  <span class="Constant">load-ingredients</span>
+<a name="L510"></a><span id="L510" class="LineNr">510 </span>  last:&amp;:duplex-list:_elem <span class="Special">&lt;-</span> last in
+<a name="L511"></a><span id="L511" class="LineNr">511 </span>  *last <span class="Special">&lt;-</span> put *last, <span class="Constant">next:offset</span>, new
+<a name="L512"></a><span id="L512" class="LineNr">512 </span>  <span class="muControl">return-unless</span> new
+<a name="L513"></a><span id="L513" class="LineNr">513 </span>  *new <span class="Special">&lt;-</span> put *new, <span class="Constant">prev:offset</span>, last
+<a name="L514"></a><span id="L514" class="LineNr">514 </span>]
+<a name="L515"></a><span id="L515" class="LineNr">515 </span>
+<a name="L516"></a><span id="L516" class="LineNr">516 </span><span class="muRecipe">def</span> last in:&amp;:duplex-list:_elem<span class="muRecipe"> -&gt; </span>result:&amp;:duplex-list:_elem [
+<a name="L517"></a><span id="L517" class="LineNr">517 </span>  <span class="Constant">local-scope</span>
+<a name="L518"></a><span id="L518" class="LineNr">518 </span>  <span class="Constant">load-ingredients</span>
+<a name="L519"></a><span id="L519" class="LineNr">519 </span>  result <span class="Special">&lt;-</span> copy in
+<a name="L520"></a><span id="L520" class="LineNr">520 </span>  <span class="Delimiter">{</span>
+<a name="L521"></a><span id="L521" class="LineNr">521 </span>    next:&amp;:duplex-list:_elem <span class="Special">&lt;-</span> next result
+<a name="L522"></a><span id="L522" class="LineNr">522 </span>    <span class="muControl">break-unless</span> next
+<a name="L523"></a><span id="L523" class="LineNr">523 </span>    result <span class="Special">&lt;-</span> copy next
+<a name="L524"></a><span id="L524" class="LineNr">524 </span>    <span class="muControl">loop</span>
+<a name="L525"></a><span id="L525" class="LineNr">525 </span>  <span class="Delimiter">}</span>
+<a name="L526"></a><span id="L526" class="LineNr">526 </span>]
+<a name="L527"></a><span id="L527" class="LineNr">527 </span>
+<a name="L528"></a><span id="L528" class="LineNr">528 </span><span class="Comment"># helper for debugging</span>
+<a name="L529"></a><span id="L529" class="LineNr">529 </span><span class="muRecipe">def</span> dump-from x:&amp;:duplex-list:_elem [
+<a name="L530"></a><span id="L530" class="LineNr">530 </span>  <span class="Constant">local-scope</span>
+<a name="L531"></a><span id="L531" class="LineNr">531 </span>  <span class="Constant">load-ingredients</span>
+<a name="L532"></a><span id="L532" class="LineNr">532 </span>  $print x, <span class="Constant">[: ]</span>
+<a name="L533"></a><span id="L533" class="LineNr">533 </span>  <span class="Delimiter">{</span>
+<a name="L534"></a><span id="L534" class="LineNr">534 </span>    <span class="muControl">break-unless</span> x
+<a name="L535"></a><span id="L535" class="LineNr">535 </span>    c:_elem <span class="Special">&lt;-</span> get *x, <span class="Constant">value:offset</span>
+<a name="L536"></a><span id="L536" class="LineNr">536 </span>    $print c, <span class="Constant">[ ]</span>
+<a name="L537"></a><span id="L537" class="LineNr">537 </span>    x <span class="Special">&lt;-</span> next x
+<a name="L538"></a><span id="L538" class="LineNr">538 </span>    <span class="Delimiter">{</span>
+<a name="L539"></a><span id="L539" class="LineNr">539 </span>      is-newline?:bool <span class="Special">&lt;-</span> equal c, <span class="Constant">10/newline</span>
+<a name="L540"></a><span id="L540" class="LineNr">540 </span>      <span class="muControl">break-unless</span> is-newline?
+<a name="L541"></a><span id="L541" class="LineNr">541 </span>      $print <span class="Constant">10/newline</span>
+<a name="L542"></a><span id="L542" class="LineNr">542 </span>      $print x, <span class="Constant">[: ]</span>
+<a name="L543"></a><span id="L543" class="LineNr">543 </span>    <span class="Delimiter">}</span>
+<a name="L544"></a><span id="L544" class="LineNr">544 </span>    <span class="muControl">loop</span>
+<a name="L545"></a><span id="L545" class="LineNr">545 </span>  <span class="Delimiter">}</span>
+<a name="L546"></a><span id="L546" class="LineNr">546 </span>  $print <span class="Constant">10/newline</span>, <span class="Constant">[---]</span>, <span class="Constant">10/newline</span>
+<a name="L547"></a><span id="L547" class="LineNr">547 </span>]
 </pre>
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