## 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, screen:&:screen -> errors-found?:bool, env:&:environment, screen:&:screen [
  local-scope
  load-ingredients
  recipes:&:editor <- get *env, recipes:offset
  in:text <- editor-contents recipes
  save [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 1/true
    return
  }
  errors-found? <- copy 0/false
]

before <render-components-end> [
  trace 11, [app], [render status]
  recipe-errors:text <- get *env, recipe-errors:offset
  {
    break-unless recipe-errors
    update-status screen, [errors found     ], 1/red
  }
]

before <render-recipe-components-end> [
  {
    recipe-errors:text <- get *env, recipe-errors:offset
    break-unless recipe-errors
    row, screen <- render-text screen, recipe-errors, left, right, 1/red, row
  }
]

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 <run-sandboxes-begin> [
  *env <- put *env, error-index:offset, -1
]

before <run-sandboxes-end> [
  {
    error-index:num <- get *env, error-index:offset
    sandboxes-completed-successfully?:bool <- equal error-index, -1
    break-if sandboxes-completed-successfully?
    errors-found? <- copy 1/true
  }
]

before <render-components-end> [
  {
    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-ingredients
  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?:bool
    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
  recipes:text <- new [ 
recipe foo [
  get 123:num, foo:offset
]]
  env:&:environment <- new-programming-environment screen, recipes, [foo]
  assume-console [
    press F4
  ]
  run [
    event-loop screen, console, env
  ]
  screen-should-contain [
    .  errors found                                                                   run (F4)           .
    .                                                  ╎foo                                              .
    .recipe 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-updates-status-with-first-erroneous-sandbox [
  local-scope
  trace-until 100/app  # trace too long
  assume-screen 100/width, 15/height
  env:&:environment <- new-programming-environment screen, [], []
  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
  ]
  # 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
  env:&:environment <- new-programming-environment screen, [], []
  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
  ]
  # 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
  env:&:environment <- new-programming-environment screen, [], [get foo, x:offset]  # invalid
  assume-console [
    press F4  # generate error
  ]
  run [
    event-loop screen, console, env
  ]
  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
  ]
  # error should disappear
  screen-should-contain [
    .                                                                                 run (F4)           .
    .                                                  ╎                                                 .
    .╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╎─────────────────────────────────────────────────.
    .                                                  ╎0   edit          copy            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
  recipes:text <- new [recipe foo x:_elem -> z:_elem [
local-scope
load-ingredients
y:&:num <- copy 0
z <- add x, y
]]
  env:&:environment <- new-programming-environment screen, recipes, [foo 2]
  assume-console [
    press F4
  ]
  event-loop screen, console, env
  screen-should-contain [
    .  errors found (0)                                                               run (F4)           .
    .recipe foo x:_elem -> z:_elem [                   ╎                                                 .
    .local-scope                                       ╎─────────────────────────────────────────────────.
    .load-ingredients                                  ╎0   edit          copy            delete         .
    .y:&:num <- copy 0                                 ╎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
  ]
  # 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            delete         .
    .y:&:num <- copy 0                                 ╎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
  recipes:text <- new [recipe length l:&:list:_elem -> n:num [
]]
  # call code that uses other variants of it, but not it itself
  sandbox:text <- new [x:&:list:num <- copy 0
to-text x]
  env:&:environment <- new-programming-environment screen, recipes, sandbox
  # run it once
  assume-console [
    press F4
  ]
  event-loop screen, console, env
  # 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
  ]
  # 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
  recipes:text <- new [ 
recipe foo [
  x <- copy 0
]]
  env:&:environment <- new-programming-environment screen, recipes, [foo]
  assume-console [
    press F4
  ]
  run [
    event-loop screen, console, env
  ]
  screen-should-contain [
    .  errors found                                                                   run (F4)           .
    .                                                  ╎foo                                              .
    .recipe foo [                                      ╎─────────────────────────────────────────────────.
    .  x <- copy 0                                     ╎                                                 .
    .]                                                 ╎                                                 .
    .foo: missing type for 'x' in 'x <- copy 0'        ╎                                                 .
  ]
]

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 '[')
  recipes:text <- new [ 
recipe foo \\[
  x <- copy 0
]
  env:&:environment <- new-programming-environment screen, recipes, [foo]
  assume-console [
    press F4
  ]
  run [
    event-loop screen, console, env
  ]
  screen-should-contain [
    .  errors found                                                                   run (F4)           .
    .                                                  ╎foo                                              .
    .recipe 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
  recipes:text <- new [ 
recipe foo [
  local-scope
  x:&:point <- new point:type
  get x:&:point, 1:offset
]]
  env:&:environment <- new-programming-environment screen, recipes, [foo]
  assume-console [
    press F4
  ]
  run [
    event-loop screen, console, env
  ]
  screen-should-contain [
    .  errors found                                                                   run (F4)           .
    .                                                  ╎foo                                              .
    .recipe 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
  recipes:text <- new [ 
recipe foo [
  local-scope
  x:num <- copy 0
  y:&:point <- new point:type
  get *y:&:point, x:num
]]
  env:&:environment <- new-programming-environment screen, recipes, [foo]
  assume-console [
    press F4
  ]
  run [
    event-loop screen, console, env
  ]
  screen-should-contain [
    .  errors found                                                                   run (F4)           .
    .                                                  ╎foo                                              .
    .recipe 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-everytime [
  local-scope
  trace-until 100/app  # trace too long
  # try to run a file with an error
  assume-screen 100/width, 15/height
  recipes:text <- new [ 
recipe foo [
  local-scope
  x:num <- copy y:num
]]
  env:&:environment <- new-programming-environment screen, recipes, [foo]
  assume-console [
    press F4
  ]
  event-loop screen, console, env
  screen-should-contain [
    .  errors found                                                                   run (F4)           .
    .                                                  ╎foo                                              .
    .recipe 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
  ]
  screen-should-contain [
    .  errors found                                                                   run (F4)           .
    .                                                  ╎foo                                              .
    .recipe 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-instruction-and-print-errors [
  local-scope
  trace-until 100/app  # trace too long
  assume-screen 100/width, 10/height
  # right editor contains an illegal instruction
  sandbox:text <- new [get 1234:num, foo:offset]
  env:&:environment <- new-programming-environment screen, [], sandbox
  # run the code in the editors
  assume-console [
    press F4
  ]
  run [
    event-loop screen, console, env
  ]
  # check that screen prints error message in red
  screen-should-contain [
    .  errors found (0)                                                               run (F4)           .
    .                                                  ╎                                                 .
    .╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╎─────────────────────────────────────────────────.
    .                                                  ╎0   edit          copy            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
  # right editor contains an illegal instruction
  sandbox:text <- new [get 1234:num, foo:offset]
  env:&:environment <- new-programming-environment screen, [], sandbox
  # run the code in the editors multiple times
  assume-console [
    press F4
    press F4
  ]
  run [
    event-loop screen, console, env
  ]
  # check that screen prints error message just once
  screen-should-contain [
    .  errors found (0)                                                               run (F4)           .
    .                                                  ╎                                                 .
    .╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╎─────────────────────────────────────────────────.
    .                                                  ╎0   edit          copy            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
  # left editor is empty
  recipes:text <- new [recipe foo [
  {
    loop
  }
]]
  # right editor contains an instruction
  env:&:environment <- new-programming-environment screen, recipes, [foo]
  # run the sandbox
  assume-console [
    press F4
  ]
  run [
    event-loop screen, console, env
  ]
  screen-should-contain [
    .  errors found (0)                                                               run (F4)           .
    .recipe foo [                                      ╎                                                 .
    .  {                                               ╎─────────────────────────────────────────────────.
    .    loop                                          ╎0   edit          copy            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
  recipes:text <- new [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 screen, recipes, [foo 4, 0]
  # run
  assume-console [
    press F4
  ]
  event-loop screen, console, env
  # screen prints error message
  screen-should-contain [
    .  errors found (0)                                                               run (F4)           .
    .recipe foo [                                      ╎                                                 .
    .local-scope                                       ╎─────────────────────────────────────────────────.
    .a:num <- next-ingredient                          ╎0   edit          copy            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
  ]
  # screen should expand trace
  screen-should-contain [
    .  errors found (0)                                                               run (F4)           .
    .recipe foo [                                      ╎                                                 .
    .local-scope                                       ╎─────────────────────────────────────────────────.
    .a:num <- next-ingredient                          ╎0   edit          copy            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'                                  .
    .╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╎─────────────────────────────────────────────────.
  ]
]