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-rw-r--r--archive/2.vm/edit/011-errors.mu886
1 files changed, 886 insertions, 0 deletions
diff --git a/archive/2.vm/edit/011-errors.mu b/archive/2.vm/edit/011-errors.mu
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+## handling malformed programs
+
+container environment [
+  recipe-errors:text
+]
+
+# copy code from recipe editor, persist to disk, load, save any errors
+def! update-recipes env:&:environment, resources:&:resources, screen:&:screen -> errors-found?:bool, env:&:environment, resources:&:resources, screen:&:screen [
+  local-scope
+  load-inputs
+  recipes:&:editor <- get *env, recipes:offset
+  in:text <- editor-contents recipes
+  resources <- dump resources, [lesson/recipes.mu], in
+  recipe-errors:text <- reload in
+  *env <- put *env, recipe-errors:offset, recipe-errors
+  # if recipe editor has errors, stop
+  {
+    break-unless recipe-errors
+    update-status screen, [errors found     ], 1/red
+    errors-found? <- copy true
+    return
+  }
+  errors-found? <- copy false
+]
+
+after <begin-run-sandboxes-on-F4> [
+  old-recipe-errors:text <- get *env, recipe-errors:offset
+]
+before <end-run-sandboxes-on-F4> [
+  # if there were recipe errors before, check if we can clear them
+  {
+    break-unless old-recipe-errors
+    screen <- render-recipes screen, env, render
+  }
+  render-recipe-errors env, screen
+]
+
+before <end-render-recipe-components> [
+  row <- render-recipe-errors env, screen
+]
+
+def render-recipe-errors env:&:environment, screen:&:screen -> row:num, screen:&:screen [
+  local-scope
+  load-inputs
+  recipe-errors:text <- get *env, recipe-errors:offset
+  recipes:&:editor <- get *env, recipes:offset
+  row:num <- get *recipes, bottom:offset
+  row <- add row, 1
+  return-unless recipe-errors
+  left:num <- get *recipes, left:offset
+  right:num <- get *recipes, right: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
+  row <- add row, 1
+  clear-screen-from screen, row, left, left, right
+]
+
+container environment [
+  error-index:num  # index of first sandbox with an error (or -1 if none)
+]
+
+after <programming-environment-initialization> [
+  *result <- put *result, error-index:offset, -1
+]
+
+after <begin-run-sandboxes> [
+  *env <- put *env, error-index:offset, -1
+]
+
+before <end-run-sandboxes> [
+  {
+    error-index:num <- get *env, error-index:offset
+    sandboxes-completed-successfully?:bool <- equal error-index, -1
+    break-if sandboxes-completed-successfully?
+    errors-found? <- copy true
+  }
+]
+
+before <end-run-sandboxes-on-F4> [
+  {
+    break-unless error?
+    recipe-errors:text <- get *env, recipe-errors:offset
+    break-if recipe-errors
+    error-index:num <- get *env, error-index:offset
+    sandboxes-completed-successfully?:bool <- equal error-index, -1
+    break-if sandboxes-completed-successfully?
+    error-index-text:text <- to-text error-index
+    status:text <- interpolate [errors found (_)    ], error-index-text
+    update-status screen, status, 1/red
+  }
+]
+
+container sandbox [
+  errors:text
+]
+
+def! update-sandbox sandbox:&:sandbox, env:&:environment, idx:num -> sandbox:&:sandbox, env:&:environment [
+  local-scope
+  load-inputs
+  data:text <- get *sandbox, data:offset
+  response:text, errors:text, fake-screen:&:screen, trace:text, completed?:bool <- run-sandboxed data
+  *sandbox <- put *sandbox, response:offset, response
+  *sandbox <- put *sandbox, errors:offset, errors
+  *sandbox <- put *sandbox, screen:offset, fake-screen
+  *sandbox <- put *sandbox, trace:offset, trace
+  {
+    break-if errors
+    break-if completed?
+    errors <- new [took too long!
+]
+    *sandbox <- put *sandbox, errors:offset, errors
+  }
+  {
+    break-unless errors
+    error-index:num <- get *env, error-index:offset
+    error-not-set?:bool <- equal error-index, -1
+    break-unless error-not-set?
+    *env <- put *env, error-index:offset, idx
+  }
+]
+
+# make sure we render any trace
+after <render-sandbox-trace-done> [
+  {
+    sandbox-errors:text <- get *sandbox, errors:offset
+    break-unless sandbox-errors
+    *sandbox <- put *sandbox, response-starting-row-on-screen:offset, 0  # no response
+    row, screen <- render-text screen, sandbox-errors, left, right, 1/red, row
+    # don't try to print anything more for this sandbox
+    jump +render-sandbox-end
+  }
+]
+
+scenario run-shows-errors-in-get [
+  local-scope
+  trace-until 100/app  # trace too long
+  assume-screen 100/width, 15/height
+  assume-resources [
+    [lesson/recipes.mu] <- [
+      |recipe foo [|
+      |  get 123:num, foo:offset|
+      |]|
+    ]
+  ]
+  env:&:environment <- new-programming-environment resources, screen, [foo]
+  render-all screen, env, render
+  screen-should-contain [
+    .                                                                                 run (F4)           .
+    .recipe foo [                                      ┊foo                                              .
+    .  get 123:num, foo:offset                         ┊─────────────────────────────────────────────────.
+    .]                                                 ┊                                                 .
+    .                                                  ┊                                                 .
+    .┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┊                                                 .
+    .                                                  ┊                                                 .
+  ]
+  assume-console [
+    press F4
+  ]
+  run [
+    event-loop screen, console, env, resources
+  ]
+  screen-should-contain [
+    .  errors found                                                                   run (F4)           .
+    .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'                            ┊                                                 .
+    .┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┊                                                 .
+    .                                                  ┊                                                 .
+  ]
+  screen-should-contain-in-color 1/red, [
+    .  errors found                                                                                      .
+    .                                                                                                    .
+    .                                                                                                    .
+    .                                                                                                    .
+    .                                                                                                    .
+    .foo: unknown element 'foo' in container 'number'                                                    .
+    .foo: first ingredient of 'get' should be a contai                                                   .
+    .ner, but got '123:num'                                                                              .
+    .                                                                                                    .
+  ]
+]
+
+scenario run-shows-errors-without-final-newline-in-recipe-side [
+  local-scope
+  trace-until 100/app  # trace too long
+  assume-screen 100/width, 15/height
+  assume-resources [
+  ]
+  env:&:environment <- new-programming-environment resources, screen
+  render-all screen, env, render
+  assume-console [
+    type [recipe foo x [
+]]
+    press F4
+  ]
+  run [
+    event-loop screen, console, env, resources
+  ]
+  screen-should-contain [
+    .  errors found                                                                   run (F4)           .
+    .recipe foo x [                                    ┊                                                 .
+    .]                                                 ┊─────────────────────────────────────────────────.
+    .foo: ingredient 'x' has no type                   ┊                                                 .
+    .┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┊                                                 .
+    .                                                  ┊                                                 .
+  ]
+]
+
+scenario run-updates-status-with-first-erroneous-sandbox [
+  local-scope
+  trace-until 100/app  # trace too long
+  assume-screen 100/width, 15/height
+  assume-resources [
+  ]
+  env:&:environment <- new-programming-environment resources, screen, []
+  render-all screen, env, render
+  assume-console [
+    left-click 3, 80
+    # create invalid sandbox 1
+    type [get foo, x:offset]
+    press F4
+    # create invalid sandbox 0
+    type [get foo, x:offset]
+    press F4
+  ]
+  run [
+    event-loop screen, console, env, resources
+  ]
+  # status line shows that error is in first sandbox
+  screen-should-contain [
+    .  errors found (0)                                                               run (F4)           .
+  ]
+]
+
+scenario run-updates-status-with-first-erroneous-sandbox-2 [
+  local-scope
+  trace-until 100/app  # trace too long
+  assume-screen 100/width, 15/height
+  assume-resources [
+  ]
+  env:&:environment <- new-programming-environment resources, screen, []
+  render-all screen, env, render
+  assume-console [
+    left-click 3, 80
+    # create invalid sandbox 2
+    type [get foo, x:offset]
+    press F4
+    # create invalid sandbox 1
+    type [get foo, x:offset]
+    press F4
+    # create valid sandbox 0
+    type [add 2, 2]
+    press F4
+  ]
+  run [
+    event-loop screen, console, env, resources
+  ]
+  # status line shows that error is in second sandbox
+  screen-should-contain [
+    .  errors found (1)                                                               run (F4)           .
+  ]
+]
+
+scenario run-hides-errors-from-past-sandboxes [
+  local-scope
+  trace-until 100/app  # trace too long
+  assume-screen 100/width, 15/height
+  assume-resources [
+  ]
+  env:&:environment <- new-programming-environment resources, screen, [get foo, x:offset]  # invalid
+  render-all screen, env, render
+  assume-console [
+    press F4  # generate error
+  ]
+  event-loop screen, console, env, resources
+  assume-console [
+    left-click 3, 58
+    press ctrl-k
+    type [add 2, 2]  # valid code
+    press F4  # update sandbox
+  ]
+  run [
+    event-loop screen, console, env, resources
+  ]
+  # error should disappear
+  screen-should-contain [
+    .                                                                                 run (F4)           .
+    .                                                  ┊                                                 .
+    .┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┊─────────────────────────────────────────────────.
+    .                                                  ┊0   edit       copy       to recipe    delete    .
+    .                                                  ┊add 2, 2                                         .
+    .                                                  ┊4                                                .
+    .                                                  ┊─────────────────────────────────────────────────.
+    .                                                  ┊                                                 .
+  ]
+]
+
+scenario run-updates-errors-for-shape-shifting-recipes [
+  local-scope
+  trace-until 100/app  # trace too long
+  assume-screen 100/width, 15/height
+  # define a shape-shifting recipe with an error
+  assume-resources [
+    [lesson/recipes.mu] <- [
+      |recipe foo x:_elem -> z:_elem [|
+      |  local-scope|
+      |  load-ingredients|
+      |  y:&:num <- copy null|
+      |  z <- add x, y|
+      |]|
+    ]
+  ]
+  env:&:environment <- new-programming-environment resources, screen, [foo 2]
+  render-all screen, env, render
+  assume-console [
+    press F4
+  ]
+  event-loop screen, console, env, resources
+  screen-should-contain [
+    .  errors found (0)                                                               run (F4)           .
+    .recipe foo x:_elem -> z:_elem [                   ┊                                                 .
+    .  local-scope                                     ┊─────────────────────────────────────────────────.
+    .  load-ingredients                                ┊0   edit       copy       to recipe    delete    .
+    .  y:&:num <- copy null                            ┊foo 2                                            .
+    .  z <- add x, y                                   ┊foo_2: 'add' requires number ingredients, but go↩.
+    .]                                                 ┊t 'y'                                            .
+    .                                                  ┊─────────────────────────────────────────────────.
+    .┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┊                                                 .
+    .                                                  ┊                                                 .
+  ]
+  # now rerun everything
+  assume-console [
+    press F4
+  ]
+  run [
+    event-loop screen, console, env, resources
+  ]
+  # error should remain unchanged
+  screen-should-contain [
+    .  errors found (0)                                                               run (F4)           .
+    .recipe foo x:_elem -> z:_elem [                   ┊                                                 .
+    .  local-scope                                     ┊─────────────────────────────────────────────────.
+    .  load-ingredients                                ┊0   edit       copy       to recipe    delete    .
+    .  y:&:num <- copy null                            ┊foo 2                                            .
+    .  z <- add x, y                                   ┊foo_3: 'add' requires number ingredients, but go↩.
+    .]                                                 ┊t 'y'                                            .
+    .                                                  ┊─────────────────────────────────────────────────.
+    .┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┊                                                 .
+    .                                                  ┊                                                 .
+  ]
+]
+
+scenario run-avoids-spurious-errors-on-reloading-shape-shifting-recipes [
+  local-scope
+  trace-until 100/app  # trace too long
+  assume-screen 100/width, 15/height
+  # overload a well-known shape-shifting recipe
+  assume-resources [
+    [lesson/recipes.mu] <- [
+      |recipe length l:&:list:_elem -> n:num [|
+      |]|
+    ]
+  ]
+  # call code that uses other variants of it, but not it itself
+  test-sandbox:text <- new [x:&:list:num <- copy null
+to-text x]
+  env:&:environment <- new-programming-environment resources, screen, test-sandbox
+  render-all screen, env, render
+  # run it once
+  assume-console [
+    press F4
+  ]
+  event-loop screen, console, env, resources
+  # no errors anywhere on screen (can't check anything else, since to-text will return an address)
+  screen-should-contain-in-color 1/red, [
+    .                                                                                                    .
+    .                                                                                                    .
+    .                                                                                                    .
+    .                                                                                                    .
+    .                                                                <-                                  .
+    .                                                                                                    .
+    .                                                                                                    .
+    .                                                                                                    .
+    .                                                                                                    .
+    .                                                                                                    .
+    .                                                                                                    .
+    .                                                                                                    .
+    .                                                                                                    .
+    .                                                                                                    .
+    .                                                                                                    .
+  ]
+  # rerun everything
+  assume-console [
+    press F4
+  ]
+  run [
+    event-loop screen, console, env, resources
+  ]
+  # still no errors
+  screen-should-contain-in-color 1/red, [
+    .                                                                                                    .
+    .                                                                                                    .
+    .                                                                                                    .
+    .                                                                                                    .
+    .                                                                <-                                  .
+    .                                                                                                    .
+    .                                                                                                    .
+    .                                                                                                    .
+    .                                                                                                    .
+    .                                                                                                    .
+    .                                                                                                    .
+    .                                                                                                    .
+    .                                                                                                    .
+    .                                                                                                    .
+    .                                                                                                    .
+  ]
+]
+
+scenario run-shows-missing-type-errors [
+  local-scope
+  trace-until 100/app  # trace too long
+  assume-screen 100/width, 15/height
+  assume-resources [
+    [lesson/recipes.mu] <- [
+      |recipe foo [|
+      |  x <- copy 0|
+      |]|
+    ]
+  ]
+  env:&:environment <- new-programming-environment resources, screen, [foo]
+  render-all screen, env, render
+  assume-console [
+    press F4
+  ]
+  run [
+    event-loop screen, console, env, resources
+  ]
+  screen-should-contain [
+    .  errors found                                                                   run (F4)           .
+    .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     ┊                                                 .
+    .┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┊                                                 .
+    .                                                  ┊                                                 .
+  ]
+]
+
+scenario run-shows-unbalanced-bracket-errors [
+  local-scope
+  trace-until 100/app  # trace too long
+  assume-screen 100/width, 15/height
+  # recipe is incomplete (unbalanced '[')
+  assume-resources [
+    [lesson/recipes.mu] <- [
+      |recipe foo \\\[|
+      |  x <- copy 0|
+    ]
+  ]
+  env:&:environment <- new-programming-environment resources, screen, [foo]
+  render-all screen, env, render
+  assume-console [
+    press F4
+  ]
+  run [
+    event-loop screen, console, env, resources
+  ]
+  screen-should-contain [
+    .  errors found                                                                   run (F4)           .
+    .recipe foo \\[                                      ┊foo                                              .
+    .  x <- copy 0                                     ┊─────────────────────────────────────────────────.
+    .                                                  ┊                                                 .
+    .9: unbalanced '\\[' for recipe                      ┊                                                 .
+    .┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┊                                                 .
+    .                                                  ┊                                                 .
+  ]
+]
+
+scenario run-shows-get-on-non-container-errors [
+  local-scope
+  trace-until 100/app  # trace too long
+  assume-screen 100/width, 15/height
+  assume-resources [
+    [lesson/recipes.mu] <- [
+      |recipe foo [|
+      |  local-scope|
+      |  x:&:point <- new point:type|
+      |  get x:&:point, 1:offset|
+      |]|
+    ]
+  ]
+  env:&:environment <- new-programming-environment resources, screen, [foo]
+  render-all screen, env, render
+  assume-console [
+    press F4
+  ]
+  run [
+    event-loop screen, console, env, resources
+  ]
+  screen-should-contain [
+    .  errors found                                                                   run (F4)           .
+    .recipe foo [                                      ┊foo                                              .
+    .  local-scope                                     ┊─────────────────────────────────────────────────.
+    .  x:&:point <- new point:type                     ┊                                                 .
+    .  get x:&:point, 1:offset                         ┊                                                 .
+    .]                                                 ┊                                                 .
+    .                                                  ┊                                                 .
+    .foo: first ingredient of 'get' should be a contai↩┊                                                 .
+    .ner, but got 'x:&:point'                          ┊                                                 .
+    .┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┊                                                 .
+    .                                                  ┊                                                 .
+  ]
+]
+
+scenario run-shows-non-literal-get-argument-errors [
+  local-scope
+  trace-until 100/app  # trace too long
+  assume-screen 100/width, 15/height
+  assume-resources [
+    [lesson/recipes.mu] <- [
+      |recipe foo [|
+      |  local-scope|
+      |  x:num <- copy 0|
+      |  y:&:point <- new point:type|
+      |  get *y:&:point, x:num|
+      |]|
+    ]
+  ]
+  env:&:environment <- new-programming-environment resources, screen, [foo]
+  render-all screen, env, render
+  assume-console [
+    press F4
+  ]
+  run [
+    event-loop screen, console, env, resources
+  ]
+  screen-should-contain [
+    .  errors found                                                                   run (F4)           .
+    .recipe foo [                                      ┊foo                                              .
+    .  local-scope                                     ┊─────────────────────────────────────────────────.
+    .  x:num <- copy 0                                 ┊                                                 .
+    .  y:&:point <- new point:type                     ┊                                                 .
+    .  get *y:&:point, x:num                           ┊                                                 .
+    .]                                                 ┊                                                 .
+    .                                                  ┊                                                 .
+    .foo: second ingredient of 'get' should have type ↩┊                                                 .
+    .'offset', but got 'x:num'                         ┊                                                 .
+    .┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┊                                                 .
+    .                                                  ┊                                                 .
+  ]
+]
+
+scenario run-shows-errors-every-time [
+  local-scope
+  trace-until 100/app  # trace too long
+  assume-screen 100/width, 15/height
+  # try to run a file with an error
+  assume-resources [
+    [lesson/recipes.mu] <- [
+      |recipe foo [|
+      |  local-scope|
+      |  x:num <- copy y:num|
+      |]|
+    ]
+  ]
+  env:&:environment <- new-programming-environment resources, screen, [foo]
+  render-all screen, env, render
+  assume-console [
+    press F4
+  ]
+  event-loop screen, console, env, resources
+  screen-should-contain [
+    .  errors found                                                                   run (F4)           .
+    .recipe foo [                                      ┊foo                                              .
+    .  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       ┊                                                 .
+    .┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┊                                                 .
+    .                                                  ┊                                                 .
+  ]
+  # rerun the file, check for the same error
+  assume-console [
+    press F4
+  ]
+  run [
+    event-loop screen, console, env, resources
+  ]
+  screen-should-contain [
+    .  errors found                                                                   run (F4)           .
+    .recipe foo [                                      ┊foo                                              .
+    .  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       ┊                                                 .
+    .┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┊                                                 .
+    .                                                  ┊                                                 .
+  ]
+]
+
+scenario run-hides-errors [
+  local-scope
+  trace-until 100/app  # trace too long
+  assume-screen 100/width, 15/height
+  # try to run a file with an error
+  assume-resources [
+    [lesson/recipes.mu] <- [
+      |recipe foo [|
+      |  local-scope|
+      |  x:num <- copy y:num|
+      |]|
+    ]
+  ]
+  env:&:environment <- new-programming-environment resources, screen, [foo]
+  render-all screen, env, render
+  assume-console [
+    press F4
+  ]
+  event-loop screen, console, env, resources
+  screen-should-contain [
+    .  errors found                                                                   run (F4)           .
+    .recipe foo [                                      ┊foo                                              .
+    .  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       ┊                                                 .
+    .┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┊                                                 .
+    .                                                  ┊                                                 .
+  ]
+  # fix the error, hit F4
+  assume-console [
+    left-click 3, 16
+    press ctrl-k
+    type [0]
+    press F4
+  ]
+  event-loop screen, console, env, resources
+  # no error anymore
+  screen-should-contain [
+    .                                                                                 run (F4)           .
+    .recipe foo [                                      ┊                                                 .
+    .  local-scope                                     ┊─────────────────────────────────────────────────.
+    .  x:num <- copy 0                                 ┊0   edit       copy       to recipe    delete    .
+    .]                                                 ┊foo                                              .
+    .                                                  ┊─────────────────────────────────────────────────.
+    .┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┊                                                 .
+    .                                                  ┊                                                 .
+  ]
+]
+
+scenario scrolling-recipe-side-reveals-errors [
+  local-scope
+  trace-until 100/app  # trace too long
+  assume-screen 100/width, 5/height
+  # recipe overflows recipe side
+  assume-resources [
+    [lesson/recipes.mu] <- [
+      |recipe foo [|
+      |  a:num <- copy 0|  # padding to overflow recipe side
+      |  b:num <- copy 0|  # padding to overflow recipe side
+      |  get 123:num, foo:offset|  # line containing error
+      |]|
+    ]
+  ]
+  env:&:environment <- new-programming-environment resources, screen, [foo]
+  render-all screen, env, render
+  # hit F4, generating errors, then scroll down
+  assume-console [
+    press F4
+    press page-down
+  ]
+  run [
+    event-loop screen, console, env, resources
+  ]
+  # errors should be displayed
+  screen-should-contain [
+    .  errors found                                                                   run (F4)           .
+    .  get 123:num, foo:offset                         ┊foo                                              .
+    .\\]                                                 ┊─────────────────────────────────────────────────.
+    .                                                  ┊                                                 .
+    .foo: unknown element 'foo' in container 'number'  ┊                                                 .
+  ]
+]
+
+scenario run-instruction-and-print-errors [
+  local-scope
+  trace-until 100/app  # trace too long
+  assume-screen 100/width, 10/height
+  assume-resources [
+  ]
+  # sandbox editor contains an illegal instruction
+  env:&:environment <- new-programming-environment resources, screen, [get 1234:num, foo:offset]
+  render-all screen, env, render
+  assume-console [
+    press F4
+  ]
+  run [
+    event-loop screen, console, env, resources
+  ]
+  # check that screen prints error message in red
+  screen-should-contain [
+    .  errors found (0)                                                               run (F4)           .
+    .                                                  ┊                                                 .
+    .┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┊─────────────────────────────────────────────────.
+    .                                                  ┊0   edit       copy       to recipe    delete    .
+    .                                                  ┊get 1234:num, foo:offset                         .
+    .                                                  ┊unknown element 'foo' in container 'number'      .
+    .                                                  ┊first ingredient of 'get' should be a container,↩.
+    .                                                  ┊ but got '1234:num'                              .
+    .                                                  ┊─────────────────────────────────────────────────.
+    .                                                  ┊                                                 .
+  ]
+  screen-should-contain-in-color 7/white, [
+    .                                                                                                    .
+    .                                                                                                    .
+    .                                                                                                    .
+    .                                                                                                    .
+    .                                                   get 1234:num, foo:offset                         .
+    .                                                                                                    .
+    .                                                                                                    .
+    .                                                                                                    .
+  ]
+  screen-should-contain-in-color 1/red, [
+    .  errors found (0)                                                                                  .
+    .                                                                                                    .
+    .                                                                                                    .
+    .                                                                                                    .
+    .                                                                                                    .
+    .                                                   unknown element 'foo' in container 'number'      .
+    .                                                   first ingredient of 'get' should be a container, .
+    .                                                    but got '1234:num'                              .
+    .                                                                                                    .
+  ]
+  screen-should-contain-in-color 245/grey, [
+    .                                                                                                    .
+    .                                                  ┊                                                 .
+    .┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┊─────────────────────────────────────────────────.
+    .                                                  ┊                                                 .
+    .                                                  ┊                                                 .
+    .                                                  ┊                                                 .
+    .                                                  ┊                                                ↩.
+    .                                                  ┊                                                 .
+    .                                                  ┊─────────────────────────────────────────────────.
+    .                                                  ┊                                                 .
+  ]
+]
+
+scenario run-instruction-and-print-errors-only-once [
+  local-scope
+  trace-until 100/app  # trace too long
+  assume-screen 100/width, 10/height
+  assume-resources [
+  ]
+  # sandbox editor contains an illegal instruction
+  env:&:environment <- new-programming-environment resources, screen, [get 1234:num, foo:offset]
+  render-all screen, env, render
+  # run the code in the editors multiple times
+  assume-console [
+    press F4
+    press F4
+  ]
+  run [
+    event-loop screen, console, env, resources
+  ]
+  # check that screen prints error message just once
+  screen-should-contain [
+    .  errors found (0)                                                               run (F4)           .
+    .                                                  ┊                                                 .
+    .┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┊─────────────────────────────────────────────────.
+    .                                                  ┊0   edit       copy       to recipe    delete    .
+    .                                                  ┊get 1234:num, foo:offset                         .
+    .                                                  ┊unknown element 'foo' in container 'number'      .
+    .                                                  ┊first ingredient of 'get' should be a container,↩.
+    .                                                  ┊ but got '1234:num'                              .
+    .                                                  ┊─────────────────────────────────────────────────.
+    .                                                  ┊                                                 .
+  ]
+]
+
+scenario sandbox-can-handle-infinite-loop [
+  local-scope
+  trace-until 100/app  # trace too long
+  assume-screen 100/width, 20/height
+  # sandbox editor will trigger an infinite loop
+  assume-resources [
+    [lesson/recipes.mu] <- [
+      |recipe foo [|
+      |  {|
+      |    loop|
+      |  }|
+      |]|
+    ]
+  ]
+  env:&:environment <- new-programming-environment resources, screen, [foo]
+  render-all screen, env, render
+  # run the sandbox
+  assume-console [
+    press F4
+  ]
+  run [
+    event-loop screen, console, env, resources
+  ]
+  screen-should-contain [
+    .  errors found (0)                                                               run (F4)           .
+    .recipe foo [                                      ┊                                                 .
+    .  {                                               ┊─────────────────────────────────────────────────.
+    .    loop                                          ┊0   edit       copy       to recipe    delete    .
+    .  }                                               ┊foo                                              .
+    .]                                                 ┊took too long!                                   .
+    .                                                  ┊─────────────────────────────────────────────────.
+    .┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┊                                                 .
+    .                                                  ┊                                                 .
+  ]
+]
+
+scenario sandbox-with-errors-shows-trace [
+  local-scope
+  trace-until 100/app  # trace too long
+  assume-screen 100/width, 10/height
+  # generate a stash and a error
+  assume-resources [
+    [lesson/recipes.mu] <- [
+      |recipe foo [|
+      |  local-scope|
+      |  a:num <- next-ingredient|
+      |  b:num <- next-ingredient|
+      |  stash [dividing by], b|
+      |  _, c:num <- divide-with-remainder a, b|
+      |  reply b|
+      |]|
+    ]
+  ]
+  env:&:environment <- new-programming-environment resources, screen, [foo 4, 0]
+  render-all screen, env, render
+  # run
+  assume-console [
+    press F4
+  ]
+  event-loop screen, console, env, resources
+  # screen prints error message
+  screen-should-contain [
+    .  errors found (0)                                                               run (F4)           .
+    .recipe foo [                                      ┊                                                 .
+    .  local-scope                                     ┊─────────────────────────────────────────────────.
+    .  a:num <- next-ingredient                        ┊0   edit       copy       to recipe    delete    .
+    .  b:num <- next-ingredient                        ┊foo 4, 0                                         .
+    .  stash [dividing by], b                          ┊foo: divide by zero in '_, c:num <- divide-with-↩.
+    .  _, c:num <- divide-with-remainder a, b          ┊remainder a, b'                                  .
+    .  reply b                                         ┊─────────────────────────────────────────────────.
+    .]                                                 ┊                                                 .
+    .                                                  ┊                                                 .
+  ]
+  # click on the call in the sandbox
+  assume-console [
+    left-click 4, 55
+  ]
+  run [
+    event-loop screen, console, env, resources
+  ]
+  # screen should expand trace
+  screen-should-contain [
+    .  errors found (0)                                                               run (F4)           .
+    .recipe foo [                                      ┊                                                 .
+    .  local-scope                                     ┊─────────────────────────────────────────────────.
+    .  a:num <- next-ingredient                        ┊0   edit       copy       to recipe    delete    .
+    .  b:num <- next-ingredient                        ┊foo 4, 0                                         .
+    .  stash [dividing by], b                          ┊dividing by 0                                    .
+    .  _, c:num <- divide-with-remainder a, b          ┊14 instructions run                              .
+    .  reply b                                         ┊foo: divide by zero in '_, c:num <- divide-with-↩.
+    .]                                                 ┊remainder a, b'                                  .
+    .                                                  ┊─────────────────────────────────────────────────.
+  ]
+]