3954

As a blanket rule, down-arrow now stops scrolling once the bottom margin
comes on screen.

Now that we have page-wise scrolling with ctrl-f/b and line-wise
scrolling with ctrl-s/x, we don't need to conflate scroll positioning
with the arrow keys. And as a result, early students no longer have to
struggle with accidentally scrolling part of the sandbox off the screen
when there's tons of empty space available.

`move-to-next-line` is still super messy and will need further
rethinking, but this commit simplifies the codebase as a whole by
eliminating a couple of historical accidents:

  a) We only introduced scrolling past the bottom of the screen to allow
  more sandboxes to come into view before we had scrolling for the
  sandbox side.

  b) We undid scrolling past the bottom in just the recipe side to allow
  errors to come into view.

Since these historical details are now irrelevant, we no longer need
separate logic for the recipe and sandbox sides, and we don't need to
keep track of the recipe-bottom separate from the bottom margin of
arbitrary editors.

4 files changed, 65 insertions, 131 deletions

diff --git a/edit/003-shortcuts.mu b/edit/003-shortcuts.mu
index 7089a26b..ae9609a7 100644
--- a/edit/003-shortcuts.mu
+++ b/edit/003-shortcuts.mu
@@ -1360,9 +1360,31 @@ def move-to-next-line editor:&:editor, screen-height:num -> go-render?:bool, edi
   left:num <- get *editor, left:offset
   right:num <- get *editor, right:offset
   last-line:num <- subtract screen-height, 1
-  break-unless before-cursor, +try-to-scroll
+  bottom:num <- get *editor, bottom:offset
+  at-bottom-of-screen?:bool <- greater-or-equal bottom, last-line
+  {
+    break-if before-cursor
+    {
+      break-if at-bottom-of-screen?
+      return 0/don't-render
+    }
+    {
+      break-unless at-bottom-of-screen?
+      jump +try-to-scroll
+    }
+  }
   next:&:duplex-list:char <- next before-cursor
-  break-unless next, +try-to-scroll
+  {
+    break-if next
+    {
+      break-if at-bottom-of-screen?
+      return 0/don't-render
+    }
+    {
+      break-unless at-bottom-of-screen?
+      jump +try-to-scroll
+    }
+  }
   already-at-bottom?:bool <- greater-or-equal cursor-row, last-line
   {
     # if cursor not at bottom, move it
@@ -1381,7 +1403,17 @@ def move-to-next-line editor:&:editor, screen-height:num -> go-render?:bool, edi
       break-if at-newline?
       loop
     }
-    break-unless next  # at bottom of editor; scroll
+    {
+      break-if next
+      {
+        break-if at-bottom-of-screen?
+        return 0/don't-render
+      }
+      {
+        break-unless at-bottom-of-screen?
+        jump +try-to-scroll
+      }
+    }
     cursor-row <- add cursor-row, 1
     cursor-column <- copy left
     {
@@ -3012,51 +3044,10 @@ de]
     3:num/raw <- get *e, cursor-row:offset
     4:num/raw <- get *e, cursor-column:offset
   ]
-  # screen should scroll, moving cursor to end of text
+  # no change
   memory-should-contain [
-    3 <- 1
-    4 <- 2
-  ]
-  assume-console [
-    type [0]
-  ]
-  run [
-    editor-event-loop screen, console, e
-  ]
-  screen-should-contain [
-    .          .
-    .de0       .
-    .┈┈┈┈┈┈┈┈┈┈.
-    .          .
-  ]
-  # try to move down again
-  $clear-trace
-  assume-console [
-    left-click 2, 0
-    press down-arrow
-  ]
-  run [
-    editor-event-loop screen, console, e
-    3:num/raw <- get *e, cursor-row:offset
-    4:num/raw <- get *e, cursor-column:offset
-  ]
-  # screen stops scrolling because cursor is already at top
-  memory-should-contain [
-    3 <- 1
-    4 <- 3
-  ]
-  check-trace-count-for-label 0, [print-character]
-  assume-console [
-    type [1]
-  ]
-  run [
-    editor-event-loop screen, console, e
-  ]
-  screen-should-contain [
-    .          .
-    .de01      .
-    .┈┈┈┈┈┈┈┈┈┈.
-    .          .
+    3 <- 2
+    4 <- 0
   ]
 ]
 
diff --git a/edit/005-sandbox.mu b/edit/005-sandbox.mu
index e154b69c..d8058d18 100644
--- a/edit/005-sandbox.mu
+++ b/edit/005-sandbox.mu
@@ -754,60 +754,6 @@ scenario cursor-down-in-recipe-editor [
   ]
 ]
 
-# we'll not use the recipe-editor's 'bottom' element directly, because later
-# layers will add other stuff to the left side below the editor (error messages)
-
-container environment [
-  recipe-bottom:num
-]
-
-after <render-recipe-components-end> [
-  *env <- put *env, recipe-bottom:offset, row
-]
-
-after <global-keypress> [
-  {
-    break-if sandbox-in-focus?
-    down-arrow?:bool <- equal k, 65516/down-arrow
-    break-unless down-arrow?
-    recipe-editor:&:editor <- get *env, recipes:offset
-    recipe-cursor-row:num <- get *recipe-editor, cursor-row:offset
-    recipe-editor-bottom:num <- get *recipe-editor, bottom:offset
-    at-bottom-of-editor?:bool <- greater-or-equal recipe-cursor-row, recipe-editor-bottom
-    break-unless at-bottom-of-editor?
-    more-to-scroll?:bool <- more-to-scroll? env, screen
-    break-if more-to-scroll?
-    loop +next-event
-  }
-  {
-    break-if sandbox-in-focus?
-    page-down?:bool <- equal k, 65518/page-down
-    break-unless page-down?
-    more-to-scroll?:bool <- more-to-scroll? env, screen
-    break-if more-to-scroll?
-    loop +next-event
-  }
-]
-
-after <global-type> [
-  {
-    break-if sandbox-in-focus?
-    page-down?:bool <- equal k, 6/ctrl-f
-    break-unless page-down?
-    more-to-scroll?:bool <- more-to-scroll? env, screen
-    break-if more-to-scroll?
-    loop +next-event
-  }
-]
-
-def more-to-scroll? env:&:environment, screen:&:screen -> result:bool [
-  local-scope
-  load-ingredients
-  recipe-bottom:num <- get *env, recipe-bottom:offset
-  height:num <- screen-height screen
-  result <- greater-or-equal recipe-bottom, height
-]
-
 scenario scrolling-down-past-bottom-of-recipe-editor-2 [
   local-scope
   trace-until 100/app
diff --git a/edit/011-errors.mu b/edit/011-errors.mu
index 049a0853..b12286ed 100644
--- a/edit/011-errors.mu
+++ b/edit/011-errors.mu
@@ -30,7 +30,7 @@ after <render-recipe-errors-on-F4> [
     recipes:&:editor <- get *env, recipes:offset
     left:num <- get *recipes, left:offset
     right:num <- get *recipes, right:offset
-    row:num <- get *env, recipe-bottom:offset
+    row:num <- get *recipes, bottom:offset
     row, screen <- render-text screen, recipe-errors, left, right, 1/red, row
     # draw dotted line after recipes
     draw-horizontal screen, row, left, right, 9480/horizontal-dotted
@@ -146,7 +146,6 @@ scenario run-shows-errors-in-get [
     .recipe foo [                                      ┊foo                                              .
     .  get 123:num, foo:offset                         ┊─────────────────────────────────────────────────.
     .]                                                 ┊                                                 .
-    .                                                  ┊                                                 .
     .foo: unknown element 'foo' in container 'number'  ┊                                                 .
     .foo: first ingredient of 'get' should be a contai↩┊                                                 .
     .ner, but got '123:num'                            ┊                                                 .
@@ -158,7 +157,6 @@ scenario run-shows-errors-in-get [
     .                                                                                                    .
     .                                                                                                    .
     .                                                                                                    .
-    .                                                                                                    .
     .foo: unknown element 'foo' in container 'number'                                                    .
     .foo: first ingredient of 'get' should be a contai                                                   .
     .ner, but got '123:num'                                                                              .
@@ -400,7 +398,6 @@ scenario run-shows-missing-type-errors [
     .recipe foo [                                      ┊foo                                              .
     .  x <- copy 0                                     ┊─────────────────────────────────────────────────.
     .]                                                 ┊                                                 .
-    .                                                  ┊                                                 .
     .foo: missing type for 'x' in 'x <- copy 0'        ┊                                                 .
     .foo: can't copy '0' to 'x'; types don't match     ┊                                                 .
     .┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┊                                                 .
@@ -431,7 +428,6 @@ scenario run-shows-unbalanced-bracket-errors [
     .  errors found                                                                   run (F4)           .
     .recipe foo \\[                                      ┊foo                                              .
     .  x <- copy 0                                     ┊─────────────────────────────────────────────────.
-    .                                                  ┊                                                 .
     .9: unbalanced '\\[' for recipe                      ┊                                                 .
     .┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┊                                                 .
     .                                                  ┊                                                 .
@@ -466,7 +462,6 @@ scenario run-shows-get-on-non-container-errors [
     .  x:&:point <- new point:type                     ┊                                                 .
     .  get x:&:point, 1:offset                         ┊                                                 .
     .]                                                 ┊                                                 .
-    .                                                  ┊                                                 .
     .foo: first ingredient of 'get' should be a contai↩┊                                                 .
     .ner, but got 'x:&:point'                          ┊                                                 .
     .┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┊                                                 .
@@ -504,7 +499,6 @@ scenario run-shows-non-literal-get-argument-errors [
     .  y:&:point <- new point:type                     ┊                                                 .
     .  get *y:&:point, x:num                           ┊                                                 .
     .]                                                 ┊                                                 .
-    .                                                  ┊                                                 .
     .foo: second ingredient of 'get' should have type ↩┊                                                 .
     .'offset', but got 'x:num'                         ┊                                                 .
     .┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┊                                                 .
@@ -537,7 +531,6 @@ scenario run-shows-errors-everytime [
     .  local-scope                                     ┊─────────────────────────────────────────────────.
     .  x:num <- copy y:num                             ┊                                                 .
     .]                                                 ┊                                                 .
-    .                                                  ┊                                                 .
     .foo: tried to read ingredient 'y' in 'x:num <- co↩┊                                                 .
     .py y:num' but it hasn't been written to yet       ┊                                                 .
     .┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┊                                                 .
@@ -556,7 +549,6 @@ scenario run-shows-errors-everytime [
     .  local-scope                                     ┊─────────────────────────────────────────────────.
     .  x:num <- copy y:num                             ┊                                                 .
     .]                                                 ┊                                                 .
-    .                                                  ┊                                                 .
     .foo: tried to read ingredient 'y' in 'x:num <- co↩┊                                                 .
     .py y:num' but it hasn't been written to yet       ┊                                                 .
     .┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┊                                                 .
diff --git a/sandbox/003-shortcuts.mu b/sandbox/003-shortcuts.mu
index 6fdd70b8..adee48a7 100644
--- a/sandbox/003-shortcuts.mu
+++ b/sandbox/003-shortcuts.mu
@@ -1348,38 +1348,43 @@ def move-to-next-line editor:&:editor, screen-height:num -> editor:&:editor [
   left:num <- get *editor, left:offset
   right:num <- get *editor, right:offset
   last-line:num <- subtract screen-height, 1
+  bottom:num <- get *editor, bottom:offset
+  at-bottom-of-screen?:bool <- greater-or-equal bottom, last-line
+  return-unless before-cursor
+  next:&:duplex-list:char <- next before-cursor
+  return-unless next
   already-at-bottom?:bool <- greater-or-equal cursor-row, last-line
-    # incorrect indent to help diff with edit/
     # if cursor not at bottom, move it
     return-if already-at-bottom?
-    # scan to start of next line, then to right column or until end of line
-    max:num <- subtract right, left
-    next-line:&:duplex-list:char <- before-start-of-next-line before-cursor, max
-    # already at end of buffer? do nothing
-    no-motion?:bool <- equal next-line, before-cursor
-    return-if no-motion?
-    cursor-row <- add cursor-row, 1
-    *editor <- put *editor, cursor-row:offset, cursor-row
-    before-cursor <- copy next-line
-    *editor <- put *editor, before-cursor:offset, before-cursor
     target-column:num <- copy cursor-column
+    # scan to start of next line
+    {
+      next:&:duplex-list:char <- next before-cursor
+      break-unless next
+      done?:bool <- greater-or-equal cursor-column, right
+      break-if done?
+      cursor-column <- add cursor-column, 1
+      before-cursor <- copy next
+      c:char <- get *next, value:offset
+      at-newline?:bool <- equal c, 10/newline
+      break-if at-newline?
+      loop
+    }
+    return-unless next
+    cursor-row <- add cursor-row, 1
     cursor-column <- copy left
-    *editor <- put *editor, cursor-column:offset, cursor-column
     {
+      next:&:duplex-list:char <- next before-cursor
+      break-unless next
       done?:bool <- greater-or-equal cursor-column, target-column
       break-if done?
-      curr:&:duplex-list:char <- next before-cursor
-      break-unless curr
-      currc:char <- get *curr, value:offset
-      at-newline?:bool <- equal currc, 10/newline
-      break-if at-newline?
-      #
-      before-cursor <- copy curr
-      *editor <- put *editor, before-cursor:offset, before-cursor
       cursor-column <- add cursor-column, 1
-      *editor <- put *editor, cursor-column:offset, cursor-column
+      before-cursor <- copy next
       loop
     }
+    *editor <- put *editor, before-cursor:offset, before-cursor
+    *editor <- put *editor, cursor-column:offset, cursor-column
+    *editor <- put *editor, cursor-row:offset, cursor-row
 ]
 
 scenario editor-adjusts-column-at-next-line [