1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
|
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
<html>
<head>
<meta http-equiv="content-type" content="text/html; charset=UTF-8">
<title>Mu - exception2.mu</title>
<meta name="Generator" content="Vim/8.0">
<meta name="plugin-version" content="vim7.4_v2">
<meta name="syntax" content="none">
<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">
<!--
pre { white-space: pre-wrap; font-family: monospace; color: #aaaaaa; background-color: #080808; }
body { font-size: 12pt; font-family: monospace; color: #aaaaaa; background-color: #080808; }
a { color:#eeeeee; text-decoration: none; }
a:hover { text-decoration: underline; }
* { font-size: 12pt; font-size: 1em; }
.muControl { color: #c0a020; }
.muRecipe { color: #ff8700; }
.LineNr { color: #444444; }
.muData { color: #ffff00; }
.Delimiter { color: #800080; }
.Constant { color: #00a0a0; }
.Special { color: #c00000; }
.Comment { color: #9090ff; }
.Comment a { color:#0000ee; text-decoration:underline; }
-->
</style>
<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 onload='JumpToLine();'>
<pre id='vimCodeElement'>
<span id="L1" class="LineNr"> 1 </span><span class="Comment"># Example program showing exceptions built out of delimited continuations.</span>
<span id="L2" class="LineNr"> 2 </span><span class="Comment"># Slightly less klunky than exception1.mu.</span>
<span id="L3" class="LineNr"> 3 </span>
<span id="L4" class="LineNr"> 4 </span><span class="Comment"># Since Mu is statically typed, we can't build an all-purpose higher-order</span>
<span id="L5" class="LineNr"> 5 </span><span class="Comment"># function called 'try'; it wouldn't know how many arguments the function</span>
<span id="L6" class="LineNr"> 6 </span><span class="Comment"># passed to it needs to take, what their types are, etc. Instead, until Mu</span>
<span id="L7" class="LineNr"> 7 </span><span class="Comment"># gets macros we'll directly use the continuation primitives.</span>
<span id="L8" class="LineNr"> 8 </span>
<span id="L9" class="LineNr"> 9 </span><span class="muData">exclusive-container</span> <a href='exception2.mu.html#L9'>error-or</a>:_elem [
<span id="L10" class="LineNr">10 </span> error:text
<span id="L11" class="LineNr">11 </span> value:_elem
<span id="L12" class="LineNr">12 </span>]
<span id="L13" class="LineNr">13 </span>
<span id="L14" class="LineNr">14 </span><span class="muRecipe">def</span> <a href='exception2.mu.html#L14'>main</a> [
<span id="L15" class="LineNr">15 </span> <span class="Constant">local-scope</span>
<span id="L16" class="LineNr">16 </span> <a href='exception2.mu.html#L21'>foo</a><span class="Constant"> false/no-exception</span>
<span id="L17" class="LineNr">17 </span> <a href='exception2.mu.html#L21'>foo</a><span class="Constant"> true/raise-exception</span>
<span id="L18" class="LineNr">18 </span>]
<span id="L19" class="LineNr">19 </span>
<span id="L20" class="LineNr">20 </span><span class="Comment"># example showing exception handling</span>
<span id="L21" class="LineNr">21 </span><span class="muRecipe">def</span> <a href='exception2.mu.html#L21'>foo</a> raise-exception?:bool [
<span id="L22" class="LineNr">22 </span> <span class="Constant">local-scope</span>
<span id="L23" class="LineNr">23 </span> <span class="Constant">load-inputs</span>
<span id="L24" class="LineNr">24 </span> <span class="Comment"># To run an instruction of the form:</span>
<span id="L25" class="LineNr">25 </span> <span class="Comment"># try f ...</span>
<span id="L26" class="LineNr">26 </span> <span class="Comment"># write this:</span>
<span id="L27" class="LineNr">27 </span> <span class="Comment"># call-with-continuation-mark 999/exception-tag, f, ...</span>
<span id="L28" class="LineNr">28 </span> <span class="Comment"># By convention we reserve tag 999 for exceptions.</span>
<span id="L29" class="LineNr">29 </span> <span class="Comment">#</span>
<span id="L30" class="LineNr">30 </span> <span class="Comment"># The other inputs and outputs to 'call-with-continuation-mark' depend on</span>
<span id="L31" class="LineNr">31 </span> <span class="Comment"># the function it is called with.</span>
<span id="L32" class="LineNr">32 </span> _, result:<a href='exception2.mu.html#L9'>error-or</a>:num <span class="Special"><-</span> <span class="muControl">call-with-continuation-mark</span> <span class="Constant">999/exception-tag</span>, <a href='exception2.mu.html#L47'>f</a>, raise-exception?
<span id="L33" class="LineNr">33 </span> <span class="Delimiter">{</span>
<span id="L34" class="LineNr">34 </span> val:num, normal-exit?:bool <span class="Special"><-</span> maybe-convert result, <span class="Constant">value:variant</span>
<span id="L35" class="LineNr">35 </span> <span class="muControl">break-unless</span> normal-exit?
<span id="L36" class="LineNr">36 </span> $print <span class="Constant">[normal exit; result ]</span> val <span class="Constant">10/newline</span>
<span id="L37" class="LineNr">37 </span> <span class="Delimiter">}</span>
<span id="L38" class="LineNr">38 </span> <span class="Delimiter">{</span>
<span id="L39" class="LineNr">39 </span> err:text, error-exit?:bool <span class="Special"><-</span> maybe-convert result, <span class="Constant">error:variant</span>
<span id="L40" class="LineNr">40 </span> <span class="muControl">break-unless</span> error-exit?
<span id="L41" class="LineNr">41 </span> $print <span class="Constant">[error caught: ]</span> err <span class="Constant">10/newline</span>
<span id="L42" class="LineNr">42 </span> <span class="Delimiter">}</span>
<span id="L43" class="LineNr">43 </span>]
<span id="L44" class="LineNr">44 </span>
<span id="L45" class="LineNr">45 </span><span class="Comment"># Callee function that we catch exceptions in must always return using a</span>
<span id="L46" class="LineNr">46 </span><span class="Comment"># continuation.</span>
<span id="L47" class="LineNr">47 </span><span class="muRecipe">def</span> <a href='exception2.mu.html#L47'>f</a> raise-exception?:bool<span class="muRecipe"> -> </span>result:<a href='exception2.mu.html#L9'>error-or</a>:num [
<span id="L48" class="LineNr">48 </span> <span class="Constant">local-scope</span>
<span id="L49" class="LineNr">49 </span> <span class="Constant">load-inputs</span>
<span id="L50" class="LineNr">50 </span> <span class="Delimiter">{</span>
<span id="L51" class="LineNr">51 </span> <span class="muControl">break-unless</span> raise-exception?
<span id="L52" class="LineNr">52 </span> <span class="Comment"># throw/raise</span>
<span id="L53" class="LineNr">53 </span> result <span class="Special"><-</span> merge <span class="Constant">0/error</span>, <span class="Constant">[error will robinson!]</span>
<span id="L54" class="LineNr">54 </span> <span class="muControl">return-continuation-until-mark</span> <span class="Constant">999/exception-tag</span>, result
<span id="L55" class="LineNr">55 </span> <span class="Delimiter">}</span>
<span id="L56" class="LineNr">56 </span> <span class="Comment"># 'normal' return; still uses the continuation mark</span>
<span id="L57" class="LineNr">57 </span> result <span class="Special"><-</span> merge <span class="Constant">1/value</span>,<span class="Constant"> 34</span>
<span id="L58" class="LineNr">58 </span> <span class="muControl">return-continuation-until-mark</span> <span class="Constant">999/exception-tag</span>, result
<span id="L59" class="LineNr">59 </span> <span class="Comment"># dead code just to avoid errors</span>
<span id="L60" class="LineNr">60 </span> result <span class="Special"><-</span> merge <span class="Constant">1/value</span>,<span class="Constant"> 0</span>
<span id="L61" class="LineNr">61 </span> <span class="muControl"> return</span> result
<span id="L62" class="LineNr">62 </span>]
</pre>
</body>
</html>
<!-- vim: set foldmethod=manual : -->
|