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# Add the first 10 numbers, and return the result in the exit code.
#
# To run:
#   $ ./translate browse.mu
#   $ ./a.elf
# Expected result:
#   $ echo $?
#   55

fn main -> _/ebx: int {
  var result/ebx: int <- copy 0
  var i/eax: int <- copy 1
  {
    compare i, 0xa
    break-if->
    result <- add i
    i <- increment
    loop
  }
  return result
}
/a> 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 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## special shortcuts for manipulating the editor
# Some keys on the keyboard generate unicode characters, others generate
# terminfo key codes. We need to modify different places in the two cases.

# tab - insert two spaces

scenario editor-inserts-two-spaces-on-tab [
  local-scope
  assume-screen 10/width, 5/height
  s:text <- new [ab
cd]
  e:&:editor <- new-editor s, 0/left, 5/right
  editor-render screen, e
  $clear-trace
  assume-console [
    press tab
  ]
  run [
    editor-event-loop screen, console, e
  ]
  screen-should-contain [
    .          .
    .  ab      .
    .cd        .
  ]
  # we render at most two editor rows worth (one row for each space)
  check-trace-count-for-label-lesser-than 10, [print-character]
]

scenario editor-inserts-two-spaces-and-wraps-line-on-tab [
  local-scope
  assume-screen 10/width, 5/height
  e:&:editor <- new-editor [abcd], 0/left, 5/right
  editor-render screen, e
  $clear-trace
  assume-console [
    press tab
  ]
  run [
    editor-event-loop screen, console, e
  ]
  screen-should-contain [
    .          .
    .  ab     .
    .cd        .
  ]
  # we re-render the whole editor
  check-trace-count-for-label-greater-than 10, [print-character]
]

after <handle-special-character> [
  {
    tab?:bool <- equal c, 9/tab
    break-unless tab?
    <begin-insert-character>
    # todo: decompose insert-at-cursor into editor update and screen update,
    # so that 'tab' doesn't render the current line multiple times
    insert-at-cursor editor, 32/space, screen
    go-render? <- insert-at-cursor editor, 32/space, screen
    <end-insert-character>
    return
  }
]

# backspace - delete character before cursor

scenario editor-handles-backspace-key [
  local-scope
  assume-screen 10/width, 5/height
  e:&:editor <- new-editor [abc], 0/left, 10/right
  editor-render screen, e
  $clear-trace
  assume-console [
    left-click 1, 1
    press backspace
  ]
  run [
    editor-event-loop screen, console, e
    4:num/raw <- get *e, cursor-row:offset
    5:num/raw <- get *e, cursor-column:offset
  ]
  screen-should-contain [
    .          .
    .bc        .
    .┈┈┈┈┈┈┈┈┈┈.
    .          .
  ]
  memory-should-contain [
    4 <- 1
    5 <- 0
  ]
  check-trace-count-for-label 3, [print-character]  # length of original line to overwrite
]

after <handle-special-character> [
  {
    delete-previous-character?:bool <- equal c, 8/backspace
    break-unless delete-previous-character?
    <begin-backspace-character>
    go-render?:bool, backspaced-cell:&:duplex-list:char <- delete-before-cursor editor, screen
    <end-backspace-character>
    return
  }
]

# return values:
#   go-render? - whether caller needs to update the screen
#   backspaced-cell - value deleted (or 0 if nothing was deleted) so we can save it for undo, etc.
def delete-before-cursor editor:&:editor, screen:&:screen -> go-render?:bool, backspaced-cell:&:duplex-list:char, editor:&:editor, screen:&:screen [
  local-scope
  load-inputs
  before-cursor:&:duplex-list:char <- get *editor, before-cursor:offset
  data:&:duplex-list:char <- get *editor, data:offset
  # if at start of text (before-cursor at § sentinel), return
  prev:&:duplex-list:char <- prev before-cursor
  return-unless prev, false/no-more-render, null/nothing-deleted
  trace 10, [app], [delete-before-cursor]
  original-row:num <- get *editor, cursor-row:offset
  move-cursor-coordinates-left editor
  backspaced-cell:&:duplex-list:char <- copy before-cursor
  data <- remove before-cursor, data  # will also neatly trim next/prev pointers in backspaced-cell/before-cursor
  before-cursor <- copy prev
  *editor <- put *editor, before-cursor:offset, before-cursor
  screen-width:num <- screen-width screen
  cursor-row:num <- get *editor, cursor-row:offset
  cursor-column:num <- get *editor, cursor-column:offset
  # did we just backspace over a newline?
  same-row?:bool <- equal cursor-row, original-row
  return-unless same-row?, true/go-render
  left:num <- get *editor, left:offset
  right:num <- get *editor, right:offset
  curr:&:duplex-list:char <- next before-cursor
  screen <- move-cursor screen, cursor-row, cursor-column
  curr-column:num <- copy cursor-column
  {
    # hit right margin? give up and let caller render
    at-right?:bool <- greater-or-equal curr-column, right
    return-if at-right?, true/go-render
    break-unless curr
    # newline? done.
    currc:char <- get *curr, value:offset
    at-newline?:bool <- equal currc, 10/newline
    break-if at-newline?
    screen <- print screen, currc
    curr-column <- add curr-column, 1
    curr <- next curr
    loop
  }
  # we're guaranteed not to be at the right margin
  space:char <- copy 32/space
  screen <- print screen, space
  go-render? <- copy false
]

def move-cursor-coordinates-left editor:&:editor -> editor:&:editor [
  local-scope
  load-inputs
  before-cursor:&:duplex-list:char <- get *editor, before-cursor:offset
  cursor-row:num <- get *editor, cursor-row:offset
  cursor-column:num <- get *editor, cursor-column:offset
  left:num <- get *editor, left:offset
  # if not at left margin, move one character left
  {
    at-left-margin?:bool <- equal cursor-column, left
    break-if at-left-margin?
    trace 10, [app], [decrementing cursor column]
    cursor-column <- subtract cursor-column, 1
    *editor <- put *editor, cursor-column:offset, cursor-column
    return
  }
  # if at left margin, we must move to previous row:
  top-of-screen?:bool <- equal cursor-row, 1  # exclude menu bar
  {
    break-if top-of-screen?
    cursor-row <- subtract cursor-row, 1
    *editor <- put *editor, cursor-row:offset, cursor-row
  }
  {
    break-unless top-of-screen?
    # no scroll, so do nothing
  }
  {
    # case 1: if previous character was newline, figure out how long the previous line is
    previous-character:char <- get *before-cursor, value:offset
    previous-character-is-newline?:bool <- equal previous-character, 10/newline
    break-unless previous-character-is-newline?
    # compute length of previous line
    trace 10, [app], [switching to previous line]
    d:&:duplex-list:char <- get *editor, data:offset
    end-of-line:num <- previous-line-length before-cursor, d
    right:num <- get *editor, right:offset
    width:num <- subtract right, left
    wrap?:bool <- greater-than end-of-line, width
    {
      break-unless wrap?
      _, column-offset:num <- divide-with-remainder end-of-line, width
      cursor-column <- add left, column-offset
      *editor <- put *editor, cursor-column:offset, cursor-column
    }
    {
      break-if wrap?
      cursor-column <- add left, end-of-line
      *editor <- put *editor, cursor-column:offset, cursor-column
    }
    return
  }
  # case 2: if previous-character was not newline, we're just at a wrapped line
  trace 10, [app], [wrapping to previous line]
  right:num <- get *editor, right:offset
  cursor-column <- subtract right, 1  # leave room for wrap icon
  *editor <- put *editor, cursor-column:offset, cursor-column
]

# takes a pointer 'curr' into the doubly-linked list and its sentinel, counts
# the length of the previous line before the 'curr' pointer.
def previous-line-length curr:&:duplex-list:char, start:&:duplex-list:char -> result:num [
  local-scope
  load-inputs
  result:num <- copy 0
  return-unless curr
  at-start?:bool <- equal curr, start
  return-if at-start?
  {
    curr <- prev curr
    break-unless curr
    at-start?:bool <- equal curr, start
    break-if at-start?
    c:char <- get *curr, value:offset
    at-newline?:bool <- equal c, 10/newline
    break-if at-newline?
    result <- add result, 1
    loop
  }
]

scenario editor-clears-last-line-on-backspace [
  local-scope
  assume-screen 10/width, 5/height
  s:text <- new [ab
cd]
  e:&:editor <- new-editor s, 0/left, 10/right
  assume-console [
    left-click 2, 0
    press backspace
  ]
  run [
    editor-event-loop screen, console, e
    4:num/raw <- get *e, cursor-row:offset
    5:num/raw <- get *e, cursor-column:offset
  ]
  screen-should-contain [
    .          .
    .abcd      .
    .┈┈┈┈┈┈┈┈┈┈.
    .          .
  ]
  memory-should-contain [
    4 <- 1
    5 <- 2
  ]
]

scenario editor-joins-and-wraps-lines-on-backspace [
  local-scope
  assume-screen 10/width, 5/height
  # initialize editor with two long-ish but non-wrapping lines
  s:text <- new [abc def
ghi jkl]
  e:&:editor <- new-editor s, 0/left, 10/right
  editor-render screen, e
  $clear-trace
  # position the cursor at the start of the second and hit backspace
  assume-console [
    left-click 2, 0
    press backspace
  ]
  run [
    editor-event-loop screen, console, e
  ]
  # resulting single line should wrap correctly
  screen-should-contain [
    .          .
    .abc defgh.
    .i jkl     .
    .┈┈┈┈┈┈┈┈┈┈.
    .          .
  ]
]

scenario editor-wraps-long-lines-on-backspace [
  local-scope
  assume-screen 10/width, 5/height
  # initialize editor in part of the screen with a long line
  e:&:editor <- new-editor [abc def ghij], 0/left, 8/right
  editor-render screen, e
  # confirm that it wraps
  screen-should-contain [
    .          .
    .abc def  .
    . ghij     .
    .┈┈┈┈┈┈┈┈  .
  ]
  $clear-trace
  # position the cursor somewhere in the middle of the top screen line and hit backspace
  assume-console [
    left-click 1, 4
    press backspace
  ]
  run [
    editor-event-loop screen, console, e
  ]
  # resulting single line should wrap correctly and not overflow its bounds
  screen-should-contain [
    .          .
    .abcdef   .
    .ghij      .
    .┈┈┈┈┈┈┈┈  .
    .          .
  ]
]

# delete - delete character at cursor

scenario editor-handles-delete-key [
  local-scope
  assume-screen 10/width, 5/height
  e:&:editor <- new-editor [abc], 0/left, 10/right
  editor-render screen, e
  $clear-trace
  assume-console [
    press delete
  ]
  run [
    editor-event-loop screen, console, e
  ]
  screen-should-contain [
    .          .
    .bc        .
    .┈┈┈┈┈┈┈┈┈┈.
    .          .
  ]
  check-trace-count-for-label 3, [print-character]  # length of original line to overwrite
  $clear-trace
  assume-console [
    press delete
  ]
  run [
    editor-event-loop screen, console, e
  ]
  screen-should-contain [
    .          .
    .c         .
    .┈┈┈┈┈┈┈┈┈┈.
    .          .
  ]
  check-trace-count-for-label 2, [print-character]  # new length to overwrite
]

after <handle-special-key> [
  {
    delete-next-character?:bool <- equal k, 65522/delete
    break-unless delete-next-character?
    <begin-delete-character>
    go-render?:bool, deleted-cell:&:duplex-list:char <- delete-at-cursor editor, screen
    <end-delete-character>
    return
  }
]

def delete-at-cursor editor:&:editor, screen:&:screen -> go-render?:bool, deleted-cell:&:duplex-list:char, editor:&:editor, screen:&:screen [
  local-scope
  load-inputs
  before-cursor:&:duplex-list:char <- get *editor, before-cursor:offset
  data:&:duplex-list:char <- get *editor, data:offset
  deleted-cell:&:duplex-list:char <- next before-cursor
  return-unless deleted-cell, false/don't-render
  currc:char <- get *deleted-cell, value:offset
  data <- remove deleted-cell, data
  deleted-newline?:bool <- equal currc, 10/newline
  return-if deleted-newline?, true/go-render
  # wasn't a newline? render rest of line
  curr:&:duplex-list:char <- next before-cursor  # refresh after remove above
  cursor-row:num <- get *editor, cursor-row:offset
  cursor-column:num <- get *editor, cursor-column:offset
  screen <- move-cursor screen, cursor-row, cursor-column
  curr-column:num <- copy cursor-column
  screen-width:num <- screen-width screen
  {
    # hit right margin? give up and let caller render
    at-right?:bool <- greater-or-equal curr-column, screen-width
    return-if at-right?, true/go-render
    break-unless curr
    currc:char <- get *curr, value:offset
    at-newline?:bool <- equal currc, 10/newline
    break-if at-newline?
    screen <- print screen, currc
    curr-column <- add curr-column, 1
    curr <- next curr
    loop
  }
  # we're guaranteed not to be at the right margin
  space:char <- copy 32/space
  screen <- print screen, space
  go-render? <- copy false
]

# right arrow

scenario editor-moves-cursor-right-with-key [
  local-scope
  assume-screen 10/width, 5/height
  e:&:editor <- new-editor [abc], 0/left, 10/right
  editor-render screen, e
  $clear-trace
  assume-console [
    press right-arrow
    type [0]
  ]
  run [
    editor-event-loop screen, console, e
  ]
  screen-should-contain [
    .          .
    .a0bc      .
    .┈┈┈┈┈┈┈┈┈┈.
    .          .
  ]
  check-trace-count-for-label 3, [print-character]  # 0 and following characters
]

after <handle-special-key> [
  {
    move-to-next-character?:bool <- equal k, 65514/right-arrow
    break-unless move-to-next-character?
    # if not at end of text
    next-cursor:&:duplex-list:char <- next before-cursor
    break-unless next-cursor
    # scan to next character
    <begin-move-cursor>
    before-cursor <- copy next-cursor
    *editor <- put *editor, before-cursor:offset, before-cursor
    go-render?:bool <- move-cursor-coordinates-right editor, screen-height
    screen <- move-cursor screen, cursor-row, cursor-column
    undo-coalesce-tag:num <- copy 2/right-arrow
    <end-move-cursor>
    return
  }
]

def move-cursor-coordinates-right editor:&:editor, screen-height:num -> go-render?:bool, editor:&:editor [
  local-scope
  load-inputs
  before-cursor:&:duplex-list:char <- get *editor before-cursor:offset
  cursor-row:num <- get *editor, cursor-row:offset
  cursor-column:num <- get *editor, cursor-column:offset
  left:num <- get *editor, left:offset
  right:num <- get *editor, right:offset
  # if crossed a newline, move cursor to start of next row
  {
    old-cursor-character:char <- get *before-cursor, value:offset
    was-at-newline?:bool <- equal old-cursor-character, 10/newline
    break-unless was-at-newline?
    cursor-row <- add cursor-row, 1
    *editor <- put *editor, cursor-row:offset, cursor-row
    cursor-column <- copy left
    *editor <- put *editor, cursor-column:offset, cursor-column
    below-screen?:bool <- greater-or-equal cursor-row, screen-height  # must be equal
    return-unless below-screen?, false/don't-render
    cursor-row <- subtract cursor-row, 1  # bring back into screen range
    *editor <- put *editor, cursor-row:offset, cursor-row
    return true/go-render
  }
  # if the line wraps, move cursor to start of next row
  {
    # if we're at the column just before the wrap indicator
    wrap-column:num <- subtract right, 1
    at-wrap?:bool <- equal cursor-column, wrap-column
    break-unless at-wrap?
    # and if next character isn't newline
    next:&:duplex-list:char <- next before-cursor
    break-unless next
    next-character:char <- get *next, value:offset
    newline?:bool <- equal next-character, 10/newline
    break-if newline?
    cursor-row <- add cursor-row, 1
    *editor <- put *editor, cursor-row:offset, cursor-row
    cursor-column <- copy left
    *editor <- put *editor, cursor-column:offset, cursor-column
    below-screen?:bool <- greater-or-equal cursor-row, screen-height  # must be equal
    return-unless below-screen?, false/no-more-render
    cursor-row <- subtract cursor-row, 1  # bring back into screen range
    *editor <- put *editor, cursor-row:offset, cursor-row
    return true/go-render
  }
  # otherwise move cursor one character right
  cursor-column <- add cursor-column, 1
  *editor <- put *editor, cursor-column:offset, cursor-column
  go-render? <- copy false
]

scenario editor-moves-cursor-to-next-line-with-right-arrow [
  local-scope
  assume-screen 10/width, 5/height
  s:text <- new [abc
d]
  e:&:editor <- new-editor s, 0/left, 10/right
  editor-render screen, e
  $clear-trace
  # type right-arrow a few times to get to start of second line
  assume-console [
    press right-arrow
    press right-arrow
    press right-arrow
    press right-arrow  # next line
  ]
  run [
    editor-event-loop screen, console, e
  ]
  check-trace-count-for-label 0, [print-character]
  # type something and ensure it goes where it should
  assume-console [
    type [0]
  ]
  run [
    editor-event-loop screen, console, e
  ]
  screen-should-contain [
    .          .
    .abc       .
    .0d        .
    .┈┈┈┈┈┈┈┈┈┈.
    .          .
  ]
  check-trace-count-for-label 2, [print-character]  # new length of second line
]

scenario editor-moves-cursor-to-next-line-with-right-arrow-2 [
  local-scope
  assume-screen 10/width, 5/height
  s:text <- new [abc
d]
  e:&:editor <- new-editor s, 1/left, 10/right
  editor-render screen, e
  assume-console [
    press right-arrow
    press right-arrow
    press right-arrow
    press right-arrow  # next line
    type [0]
  ]
  run [
    editor-event-loop screen, console, e
  ]
  screen-should-contain [
    .          .
    . abc      .
    . 0d       .
    . ┈┈┈┈┈┈┈┈┈.
    .          .
  ]
]

scenario editor-moves-cursor-to-next-wrapped-line-with-right-arrow [
  local-scope
  assume-screen 10/width, 5/height
  e:&:editor <- new-editor [abcdef], 0/left, 5/right
  editor-render screen, e
  $clear-trace
  assume-console [
    left-click 1, 3
    press right-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-should-contain [
    .          .
    .abcd     .
    .ef        .
    .┈┈┈┈┈     .
    .          .
  ]
  memory-should-contain [
    3 <- 2
    4 <- 0
  ]
  check-trace-count-for-label 0, [print-character]
]

scenario editor-moves-cursor-to-next-wrapped-line-with-right-arrow-2 [
  local-scope
  assume-screen 10/width, 5/height
  # line just barely wrapping
  e:&:editor <- new-editor [abcde], 0/left, 5/right
  editor-render screen, e
  $clear-trace
  # position cursor at last character before wrap and hit right-arrow
  assume-console [
    left-click 1, 3
    press right-arrow
  ]
  run [
    editor-event-loop screen, console, e
    3:num/raw <- get *e, cursor-row:offset
    4:num/raw <- get *e, cursor-column:offset
  ]
  memory-should-contain [
    3 <- 2
    4 <- 0
  ]
  # now hit right arrow again
  assume-console [
    press right-arrow
  ]
  run [
    editor-event-loop screen, console, e
    3:num/raw <- get *e, cursor-row:offset
    4:num/raw <- get *e, cursor-column:offset
  ]
  memory-should-contain [
    3 <- 2
    4 <- 1
  ]
  check-trace-count-for-label 0, [print-character]
]

scenario editor-moves-cursor-to-next-wrapped-line-with-right-arrow-3 [
  local-scope
  assume-screen 10/width, 5/height
  e:&:editor <- new-editor [abcdef], 1/left, 6/right
  editor-render screen, e
  $clear-trace
  assume-console [
    left-click 1, 4
    press right-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-should-contain [
    .          .
    . abcd    .
    . ef       .
    . ┈┈┈┈┈    .
    .          .
  ]
  memory-should-contain [
    3 <- 2
    4 <- 1
  ]
  check-trace-count-for-label 0, [print-character]
]

scenario editor-moves-cursor-to-next-line-with-right-arrow-at-end-of-line [
  local-scope
  assume-screen 10/width, 5/height
  s:text <- new [abc
d]
  e:&:editor <- new-editor s, 0/left, 10/right
  editor-render screen, e
  $clear-trace
  # move to end of line, press right-arrow, type a character
  assume-console [
    left-click 1, 3
    press right-arrow
    type [0]
  ]
  run [
    editor-event-loop screen, console, e
  ]
  # new character should be in next line
  screen-should-contain [
    .          .
    .abc       .
    .0d        .
    .┈┈┈┈┈┈┈┈┈┈.
    .          .
  ]
  check-trace-count-for-label 2, [print-character]
]

# todo: ctrl-right: next word-end

# left arrow

scenario editor-moves-cursor-left-with-key [
  local-scope
  assume-screen 10/width, 5/height
  e:&:editor <- new-editor [abc], 0/left, 10/right
  editor-render screen, e
  $clear-trace
  assume-console [
    left-click 1, 2
    press left-arrow
    type [0]
  ]
  run [
    editor-event-loop screen, console, e
  ]
  screen-should-contain [
    .          .
    .a0bc      .
    .┈┈┈┈┈┈┈┈┈┈.
    .          .
  ]
  check-trace-count-for-label 3, [print-character]
]

after <handle-special-key> [
  {
    move-to-previous-character?:bool <- equal k, 65515/left-arrow
    break-unless move-to-previous-character?
    trace 10, [app], [left arrow]
    # if not at start of text (before-cursor at § sentinel)
    prev:&:duplex-list:char <- prev before-cursor
    return-unless prev, false/don't-render
    <begin-move-cursor>
    move-cursor-coordinates-left editor
    before-cursor <- copy prev
    *editor <- put *editor, before-cursor:offset, before-cursor
    undo-coalesce-tag:num <- copy 1/left-arrow
    <end-move-cursor>
    return
  }
]

scenario editor-moves-cursor-to-previous-line-with-left-arrow-at-start-of-line [
  local-scope
  assume-screen 10/width, 5/height
  # initialize editor with two lines
  s:text <- new [abc
d]
  e:&:editor <- new-editor s, 0/left, 10/right
  editor-render screen, e
  $clear-trace
  # position cursor at start of second line (so there's no previous newline)
  assume-console [
    left-click 2, 0
    press left-arrow
  ]
  run [
    editor-event-loop screen, console, e
    3:num/raw <- get *e, cursor-row:offset
    4:num/raw <- get *e, cursor-column:offset
  ]
  memory-should-contain [
    3 <- 1
    4 <- 3
  ]
  check-trace-count-for-label 0, [print-character]
]

scenario editor-moves-cursor-to-previous-line-with-left-arrow-at-start-of-line-2 [
  local-scope
  assume-screen 10/width, 5/height
  # initialize editor with three lines
  s:text <- new [abc
def
g]
  e:&:editor <- new-editor s:text, 0/left, 10/right
  editor-render screen, e
  $clear-trace
  # position cursor further down (so there's a newline before the character at
  # the cursor)
  assume-console [
    left-click 3, 0
    press left-arrow
    type [0]
  ]
  run [
    editor-event-loop screen, console, e
  ]
  screen-should-contain [
    .          .
    .abc       .
    .def0      .
    .g         .
    .┈┈┈┈┈┈┈┈┈┈.
  ]
  check-trace-count-for-label 1, [print-character]  # just the '0'
]

scenario editor-moves-cursor-to-previous-line-with-left-arrow-at-start-of-line-3 [
  local-scope
  assume-screen 10/width, 5/height
  s:text <- new [abc
def
g]
  e:&:editor <- new-editor s, 0/left, 10/right
  editor-render screen, e
  $clear-trace
  # position cursor at start of text, press left-arrow, then type a character
  assume-console [
    left-click 1, 0
    press left-arrow
    type [0]
  ]
  run [
    editor-event-loop screen, console, e
  ]
  # left-arrow should have had no effect
  screen-should-contain [
    .          .
    .0abc      .
    .def       .
    .g         .
    .┈┈┈┈┈┈┈┈┈┈.
  ]
  check-trace-count-for-label 4, [print-character]  # length of first line
]

scenario editor-moves-cursor-to-previous-line-with-left-arrow-at-start-of-line-4 [
  local-scope
  assume-screen 10/width, 5/height
  # initialize editor with text containing an empty line
  s:text <- new [abc

d]
  e:&:editor <- new-editor s, 0/left, 10/right
  editor-render screen, e:&:editor
  $clear-trace
  # position cursor right after empty line
  assume-console [
    left-click 3, 0
    press left-arrow
    type [0]
  ]
  run [
    editor-event-loop screen, console, e
  ]
  screen-should-contain [
    .          .
    .abc       .
    .0         .
    .d         .
    .┈┈┈┈┈┈┈┈┈┈.
  ]
  check-trace-count-for-label 1, [print-character]  # just the '0'
]

scenario editor-moves-across-screen-lines-across-wrap-with-left-arrow [
  local-scope
  assume-screen 10/width, 5/height
  # initialize editor with a wrapping line
  e:&:editor <- new-editor [abcdef], 0/left, 5/right
  editor-render screen, e
  $clear-trace
  screen-should-contain [
    .          .
    .abcd     .
    .ef        .
    .┈┈┈┈┈     .
    .          .
  ]
  # position cursor right after empty line
  assume-console [
    left-click 2, 0
    press left-arrow
  ]
  run [
    editor-event-loop screen, console, e
    3:num/raw <- get *e, cursor-row:offset
    4:num/raw <- get *e, cursor-column:offset
  ]
  memory-should-contain [
    3 <- 1  # previous row
    4 <- 3  # right margin except wrap icon
  ]
  check-trace-count-for-label 0, [print-character]
]

scenario editor-moves-across-screen-lines-to-wrapping-line-with-left-arrow [
  local-scope
  assume-screen 10/width, 5/height
  # initialize editor with a wrapping line followed by a second line
  s:text <- new [abcdef
g]
  e:&:editor <- new-editor s, 0/left, 5/right
  editor-render screen, e
  $clear-trace
  screen-should-contain [
    .          .
    .abcd     .
    .ef        .
    .g         .
    .┈┈┈┈┈     .
  ]
  # position cursor right after empty line
  assume-console [
    left-click 3, 0
    press left-arrow
  ]
  run [
    editor-event-loop screen, console, e
    3:num/raw <- get *e, cursor-row:offset
    4:num/raw <- get *e, cursor-column:offset
  ]
  memory-should-contain [
    3 <- 2  # previous row
    4 <- 2  # end of wrapped line
  ]
  check-trace-count-for-label 0, [print-character]
]

scenario editor-moves-across-screen-lines-to-non-wrapping-line-with-left-arrow [
  local-scope
  assume-screen 10/width, 5/height
  # initialize editor with a line on the verge of wrapping, followed by a second line
  s:text <- new [abcd
e]
  e:&:editor <- new-editor s, 0/left, 5/right
  editor-render screen, e
  $clear-trace
  screen-should-contain [
    .          .
    .abcd      .
    .e         .
    .┈┈┈┈┈     .
    .          .
  ]
  # position cursor right after empty line
  assume-console [
    left-click 2, 0
    press left-arrow
  ]
  run [
    editor-event-loop screen, console, e
    3:num/raw <- get *e, cursor-row:offset
    4:num/raw <- get *e, cursor-column:offset
  ]
  memory-should-contain [
    3 <- 1  # previous row
    4 <- 4  # end of wrapped line
  ]
  check-trace-count-for-label 0, [print-character]
]

# todo: ctrl-left: previous word-start

# up arrow

scenario editor-moves-to-previous-line-with-up-arrow [
  local-scope
  assume-screen 10/width, 5/height
  s:text <- new [abc
def]
  e:&:editor <- new-editor s, 0/left, 10/right
  editor-render screen, e
  $clear-trace
  assume-console [
    left-click 2, 1
    press up-arrow
  ]
  run [
    editor-event-loop screen, console, e
    3:num/raw <- get *e, cursor-row:offset
    4:num/raw <- get *e, cursor-column:offset
  ]
  memory-should-contain [
    3 <- 1
    4 <- 1
  ]
  check-trace-count-for-label 0, [print-character]
  assume-console [
    type [0]
  ]
  run [
    editor-event-loop screen, console, e
  ]
  screen-should-contain [
    .          .
    .a0bc      .
    .def       .
    .┈┈┈┈┈┈┈┈┈┈.
    .          .
  ]
]

after <handle-special-key> [
  {
    move-to-previous-line?:bool <- equal k, 65517/up-arrow
    break-unless move-to-previous-line?
    <begin-move-cursor>
    move-to-previous-line editor
    undo-coalesce-tag:num <- copy 3/up-arrow
    <end-move-cursor>
    return
  }
]

def move-to-previous-line editor:&:editor -> editor:&:editor [
  local-scope
  load-inputs
  cursor-row:num <- get *editor, cursor-row:offset
  cursor-column:num <- get *editor, cursor-column:offset
  before-cursor:&:duplex-list:char <- get *editor, before-cursor:offset
  left:num <- get *editor, left:offset
  right:num <- get *editor, right:offset
  already-at-top?:bool <- lesser-or-equal cursor-row, 1/top
  {
    # if cursor not at top, move it
    break-if already-at-top?
    # if not at newline, move to start of line (previous newline)
    # then scan back another line
    # if either step fails, give up without modifying cursor or coordinates
    curr:&:duplex-list:char <- copy before-cursor
    old:&:duplex-list:char <- copy curr
    {
      at-left?:bool <- equal cursor-column, left
      break-if at-left?
      curr <- before-previous-screen-line curr, editor
      no-motion?:bool <- equal curr, old
      return-if no-motion?
    }
    {
      curr <- before-previous-screen-line curr, editor
      no-motion?:bool <- equal curr, old
      return-if no-motion?
    }
    before-cursor <- copy curr
    *editor <- put *editor, before-cursor:offset, before-cursor
    cursor-row <- subtract cursor-row, 1
    *editor <- put *editor, cursor-row:offset, cursor-row
    # scan ahead to right column or until end of line
    target-column:num <- copy cursor-column
    cursor-column <- copy left
    *editor <- put *editor, cursor-column:offset, cursor-column
    {
      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
      loop
    }
  }
]

# Takes a pointer into the doubly-linked list, scans back to before start of
# previous *wrapped* line.
# Returns original if no next newline.
# Beware: never return null pointer.
def before-previous-screen-line in:&:duplex-list:char, editor:&:editor -> out:&:duplex-list:char [
  local-scope
  load-inputs
  curr:&:duplex-list:char <- copy in
  c:char <- get *curr, value:offset
  # compute max, number of characters to skip
  #   1 + len%(width-1)
  #   except rotate second term to vary from 1 to width-1 rather than 0 to width-2
  left:num <- get *editor, left:offset
  right:num <- get *editor, right:offset
  max-line-length:num <- subtract right, left, -1/exclusive-right, 1/wrap-icon
  sentinel:&:duplex-list:char <- get *editor, data:offset
  len:num <- previous-line-length curr, sentinel
  {
    break-if len
    # empty line; just skip this newline
    prev:&:duplex-list:char <- prev curr
    return-unless prev, curr
    return prev
  }
  _, max:num <- divide-with-remainder len, max-line-length
  # remainder 0 => scan one width-worth
  {
    break-if max
    max <- copy max-line-length
  }
  max <- add max, 1
  count:num <- copy 0
  # skip 'max' characters
  {
    done?:bool <- greater-or-equal count, max
    break-if done?
    prev:&:duplex-list:char <- prev curr
    break-unless prev
    curr <- copy prev
    count <- add count, 1
    loop
  }
  return curr
]

scenario editor-adjusts-column-at-previous-line [
  local-scope
  assume-screen 10/width, 5/height
  s:text <- new [ab
def]
  e:&:editor <- new-editor s, 0/left, 10/right
  editor-render screen, e
  $clear-trace
  assume-console [
    left-click 2, 3
    press up-arrow
  ]
  run [
    editor-event-loop screen, console, e
    3:num/raw <- get *e, cursor-row:offset
    4:num/raw <- get *e, cursor-column:offset
  ]
  memory-should-contain [
    3 <- 1
    4 <- 2
  ]
  check-trace-count-for-label 0, [print-character]
  assume-console [
    type [0]
  ]
  run [
    editor-event-loop screen, console, e
  ]
  screen-should-contain [
    .          .
    .ab0       .
    .def       .
    .┈┈┈┈┈┈┈┈┈┈.
    .          .
  ]
]

scenario editor-adjusts-column-at-empty-line [
  local-scope
  assume-screen 10/width, 5/height
  s:text <- new [
def]
  e:&:editor <- new-editor s, 0/left, 10/right
  editor-render screen, e
  $clear-trace
  assume-console [
    left-click 2, 3
    press up-arrow
  ]
  run [
    editor-event-loop screen, console, e
    3:num/raw <- get *e, cursor-row:offset
    4:num/raw <- get *e, cursor-column:offset
  ]
  memory-should-contain [
    3 <- 1
    4 <- 0
  ]
  check-trace-count-for-label 0, [print-character]
  assume-console [
    type [0]
  ]
  run [
    editor-event-loop screen, console, e
  ]
  screen-should-contain [
    .          .
    .0         .
    .def       .
    .┈┈┈┈┈┈┈┈┈┈.
    .          .
  ]
]

scenario editor-moves-to-previous-line-from-zero-margin [
  local-scope
  assume-screen 10/width, 5/height
  # start out with three lines
  s:text <- new [abc
def
ghi]
  e:&:editor <- new-editor s, 0/left, 10/right
  editor-render screen, e
  $clear-trace
  # click on the third line and hit up-arrow, so you end up just after a newline
  assume-console [
    left-click 3, 0
    press up-arrow
  ]
  run [
    editor-event-loop screen, console, e
    3:num/raw <- get *e, cursor-row:offset
    4:num/raw <- get *e, cursor-column:offset
  ]
  memory-should-contain [
    3 <- 2
    4 <- 0
  ]
  check-trace-count-for-label 0, [print-character]
  assume-console [
    type [0]
  ]
  run [
    editor-event-loop screen, console, e
  ]
  screen-should-contain [
    .          .
    .abc       .
    .0def      .
    .ghi       .
    .┈┈┈┈┈┈┈┈┈┈.
  ]
]

scenario editor-moves-to-previous-line-from-left-margin [
  local-scope
  assume-screen 10/width, 5/height
  # start out with three lines
  s:text <- new [abc
def
ghi]
  e:&:editor <- new-editor s, 1/left, 10/right
  editor-render screen, e
  $clear-trace
  # click on the third line and hit up-arrow, so you end up just after a newline
  assume-console [
    left-click 3, 1
    press up-arrow
  ]
  run [
    editor-event-loop screen, console, e
    3:num/raw <- get *e, cursor-row:offset
    4:num/raw <- get *e, cursor-column:offset
  ]
  memory-should-contain [
    3 <- 2
    4 <- 1
  ]
  check-trace-count-for-label 0, [print-character]
  assume-console [
    type [0]
  ]
  run [
    editor-event-loop screen, console, e
  ]
  screen-should-contain [
    .          .
    . abc      .
    . 0def     .
    . ghi      .
    . ┈┈┈┈┈┈┈┈┈.
  ]
]

scenario editor-moves-to-top-line-in-presence-of-wrapped-line [
  local-scope
  assume-screen 10/width, 5/height
  e:&:editor <- new-editor [abcde], 0/left, 5/right
  editor-render screen, e
  screen-should-contain [
    .          .
    .abcd     .
    .e         .
    .┈┈┈┈┈     .
  ]
  $clear-trace
  assume-console [
    left-click 2, 0
    press up-arrow
  ]
  run [
    editor-event-loop screen, console, e
    3:num/raw <- get *e, cursor-row:offset
    4:num/raw <- get *e, cursor-column:offset
  ]
  memory-should-contain [
    3 <- 1
    4 <- 0
  ]
  check-trace-count-for-label 0, [print-character]
  assume-console [
    type [0]
  ]
  run [
    editor-event-loop screen, console, e
  ]
  screen-should-contain [
    .          .
    .0abc     .
    .de        .
    .┈┈┈┈┈     .
  ]
]

scenario editor-moves-to-top-line-in-presence-of-wrapped-line-2 [
  local-scope
  assume-screen 10/width, 5/height
  s:text <- new [abc
defgh]
  e:&:editor <- new-editor s, 0/left, 5/right
  editor-render screen, e
  screen-should-contain [
    .          .
    .abc       .
    .defg     .
    .h         .
    .┈┈┈┈┈     .
  ]
  $clear-trace
  assume-console [
    left-click 3, 0
    press up-arrow
    press up-arrow
  ]
  run [
    editor-event-loop screen, console, e
    3:num/raw <- get *e, cursor-row:offset
    4:num/raw <- get *e, cursor-column:offset
  ]
  memory-should-contain [
    3 <- 1
    4 <- 0
  ]
  check-trace-count-for-label 0, [print-character]
  assume-console [
    type [0]
  ]
  run [
    editor-event-loop screen, console, e
  ]
  screen-should-contain [
    .          .
    .0abc      .
    .defg     .
    .h         .
    .┈┈┈┈┈     .
  ]
]

# down arrow

scenario editor-moves-to-next-line-with-down-arrow [
  local-scope
  assume-screen 10/width, 5/height
  s:text <- new [abc
def]
  e:&:editor <- new-editor s, 0/left, 10/right
  editor-render screen, e
  $clear-trace
  # cursor starts out at (1, 0)
  assume-console [
    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
  ]
  # ..and ends at (2, 0)
  memory-should-contain [
    3 <- 2
    4 <- 0
  ]
  check-trace-count-for-label 0, [print-character]
  assume-console [
    type [0]
  ]
  run [
    editor-event-loop screen, console, e
  ]
  screen-should-contain [
    .          .
    .abc       .
    .0def      .
    .┈┈┈┈┈┈┈┈┈┈.
    .          .
  ]
]

after <handle-special-key> [
  {
    move-to-next-line?:bool <- equal k, 65516/down-arrow
    break-unless move-to-next-line?
    <begin-move-cursor>
    move-to-next-line editor, screen-height
    undo-coalesce-tag:num <- copy 4/down-arrow
    <end-move-cursor>
    return
  }
]

def move-to-next-line editor:&:editor, screen-height:num -> editor:&:editor [
  local-scope
  load-inputs
  cursor-row:num <- get *editor, cursor-row:offset
  cursor-column:num <- get *editor, cursor-column:offset
  before-cursor:&:duplex-list:char <- get *editor, before-cursor:offset
  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
    # if cursor not at bottom, move it
    return-if already-at-bottom?
    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
    {
      next:&:duplex-list:char <- next before-cursor
      break-unless next
      c:char <- get *next, value:offset
      at-newline?:bool <- equal c, 10/newline
      break-if at-newline?
      done?:bool <- greater-or-equal cursor-column, target-column
      break-if done?
      cursor-column <- add cursor-column, 1
      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 [
  local-scope
  assume-screen 10/width, 5/height
  # second line is shorter than first
  s:text <- new [abcde
fg
hi]
  e:&:editor <- new-editor s, 0/left, 10/right
  editor-render screen, e
  $clear-trace
  # move to end of first line, then press down
  assume-console [
    left-click 1, 8
    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
  ]
  # cursor doesn't go vertically down, it goes to end of shorter line
  memory-should-contain [
    3 <- 2
    4 <- 2
  ]
  check-trace-count-for-label 0, [print-character]
  assume-console [
    type [0]
  ]
  run [
    editor-event-loop screen, console, e
  ]
  screen-should-contain [
    .          .
    .abcde     .
    .fg0       .
    .hi        .
    .┈┈┈┈┈┈┈┈┈┈.
  ]
]

# ctrl-a/home - move cursor to start of line

scenario editor-moves-to-start-of-line-with-ctrl-a [
  local-scope
  assume-screen 10/width, 5/height
  s:text <- new [123
456]
  e:&:editor <- new-editor s, 0/left, 10/right
  editor-render screen, e
  $clear-trace
  # start on second line, press ctrl-a
  assume-console [
    left-click 2, 3
    press ctrl-a
  ]
  run [
    editor-event-loop screen, console, e
    4:num/raw <- get *e, cursor-row:offset
    5:num/raw <- get *e, cursor-column:offset
  ]
  # cursor moves to start of line
  memory-should-contain [
    4 <- 2
    5 <- 0
  ]
  check-trace-count-for-label 0, [print-character]
]

after <handle-special-character> [
  {
    move-to-start-of-line?:bool <- equal c, 1/ctrl-a
    break-unless move-to-start-of-line?
    <begin-move-cursor>
    move-to-start-of-screen-line editor
    undo-coalesce-tag:num <- copy 0/never
    <end-move-cursor>
    return false/don't-render
  }
]

after <handle-special-key> [
  {
    move-to-start-of-line?:bool <- equal k, 65521/home
    break-unless move-to-start-of-line?
    <begin-move-cursor>
    move-to-start-of-screen-line editor
    undo-coalesce-tag:num <- copy 0/never
    <end-move-cursor>
    return false/don't-render
  }
]

# handles wrapped lines
# precondition: cursor-column should be in a consistent state
def move-to-start-of-screen-line editor:&:editor -> editor:&:editor [
  local-scope
  load-inputs
  # update cursor column
  left:num <- get *editor, left:offset
  col:num <- get *editor, cursor-column:offset
  # update before-cursor
  curr:&:duplex-list:char <- get *editor, before-cursor:offset
  # while not at start of line, move
  {
    done?:bool <- equal col, left
    break-if done?
    assert curr, [move-to-start-of-line tried to move before start of text]
    curr <- prev curr
    col <- subtract col, 1
    loop
  }
  *editor <- put *editor, cursor-column:offset, col
  *editor <- put *editor, before-cursor:offset, curr
]

scenario editor-moves-to-start-of-line-with-ctrl-a-2 [
  local-scope
  assume-screen 10/width, 5/height
  s:text <- new [123
456]
  e:&:editor <- new-editor s, 0/left, 10/right
  editor-render screen, e
  $clear-trace
  # start on first line (no newline before), press ctrl-a
  assume-console [
    left-click 1, 3
    press ctrl-a
  ]
  run [
    editor-event-loop screen, console, e
    4:num/raw <- get *e, cursor-row:offset
    5:num/raw <- get *e, cursor-column:offset
  ]
  # cursor moves to start of line
  memory-should-contain [
    4 <- 1
    5 <- 0
  ]
  check-trace-count-for-label 0, [print-character]
]

scenario editor-moves-to-start-of-line-with-home [
  local-scope
  assume-screen 10/width, 5/height
  s:text <- new [123
456]
  e:&:editor <- new-editor s, 0/left, 10/right
  $clear-trace
  # start on second line, press 'home'
  assume-console [
    left-click 2, 3
    press home
  ]
  run [
    editor-event-loop screen, console, e
    3:num/raw <- get *e, cursor-row:offset
    4:num/raw <- get *e, cursor-column:offset
  ]
  # cursor moves to start of line
  memory-should-contain [
    3 <- 2
    4 <- 0
  ]
  check-trace-count-for-label 0, [print-character]
]

scenario editor-moves-to-start-of-line-with-home-2 [
  local-scope
  assume-screen 10/width, 5/height
  s:text <- new [123
456]
  e:&:editor <- new-editor s, 0/left, 10/right
  editor-render screen, e
  $clear-trace
  # start on first line (no newline before), press 'home'
  assume-console [
    left-click 1, 3
    press home
  ]
  run [
    editor-event-loop screen, console, e
    3:num/raw <- get *e, cursor-row:offset
    4:num/raw <- get *e, cursor-column:offset
  ]
  # cursor moves to start of line
  memory-should-contain [
    3 <- 1
    4 <- 0
  ]
  check-trace-count-for-label 0, [print-character]
]

scenario editor-moves-to-start-of-screen-line-with-ctrl-a [
  local-scope
  assume-screen 10/width, 5/height
  e:&:editor <- new-editor [123456], 0/left, 5/right
  editor-render screen, e
  screen-should-contain [
    .          .
    .1234     .
    .56        .
    .┈┈┈┈┈     .
    .          .
  ]
  $clear-trace
  # start on second line, press ctrl-a then up
  assume-console [
    left-click 2, 1
    press ctrl-a
    press up-arrow
  ]
  run [
    editor-event-loop screen, console, e
    4:num/raw <- get *e, cursor-row:offset
    5:num/raw <- get *e, cursor-column:offset
  ]
  # cursor moves to start of first line
  memory-should-contain [
    4 <- 1  # cursor-row
    5 <- 0  # cursor-column
  ]
  check-trace-count-for-label 0, [print-character]
  # make sure before-cursor is in sync
  assume-console [
    type [a]
  ]
  run [
    editor-event-loop screen, console, e
    4:num/raw <- get *e, cursor-row:offset
    5:num/raw <- get *e, cursor-column:offset
  ]
  screen-should-contain [
    .          .
    .a123     .
    .456       .
    .┈┈┈┈┈     .
    .          .
  ]
  memory-should-contain [
    4 <- 1  # cursor-row
    5 <- 1  # cursor-column
  ]
]

# ctrl-e/end - move cursor to end of line

scenario editor-moves-to-end-of-line-with-ctrl-e [
  local-scope
  assume-screen 10/width, 5/height
  s:text <- new [123
456]
  e:&:editor <- new-editor s, 0/left, 10/right
  editor-render screen, e
  $clear-trace
  # start on first line, press ctrl-e
  assume-console [
    left-click 1, 1
    press ctrl-e
  ]
  run [
    editor-event-loop screen, console, e
    4:num/raw <- get *e, cursor-row:offset
    5:num/raw <- get *e, cursor-column:offset
  ]
  # cursor moves to end of line
  memory-should-contain [
    4 <- 1
    5 <- 3
  ]
  check-trace-count-for-label 0, [print-character]
  # editor inserts future characters at cursor
  assume-console [
    type [z]
  ]
  run [
    editor-event-loop screen, console, e
    4:num/raw <- get *e, cursor-row:offset
    5:num/raw <- get *e, cursor-column:offset
  ]
  memory-should-contain [
    4 <- 1
    5 <- 4
  ]
  screen-should-contain [
    .          .
    .123z      .
    .456       .
    .┈┈┈┈┈┈┈┈┈┈.
    .          .
  ]
  check-trace-count-for-label 1, [print-character]
]

after <handle-special-character> [
  {
    move-to-end-of-line?:bool <- equal c, 5/ctrl-e
    break-unless move-to-end-of-line?
    <begin-move-cursor>
    move-to-end-of-line editor
    undo-coalesce-tag:num <- copy 0/never
    <end-move-cursor>
    return false/don't-render
  }
]

after <handle-special-key> [
  {
    move-to-end-of-line?:bool <- equal k, 65520/end
    break-unless move-to-end-of-line?
    <begin-move-cursor>
    move-to-end-of-line editor
    undo-coalesce-tag:num <- copy 0/never
    <end-move-cursor>
    return false/don't-render
  }
]

def move-to-end-of-line editor:&:editor -> editor:&:editor [
  local-scope
  load-inputs
  before-cursor:&:duplex-list:char <- get *editor, before-cursor:offset
  cursor-column:num <- get *editor, cursor-column:offset
  right:num <- get *editor, right:offset
  # while not at end of line, move
  {
    next:&:duplex-list:char <- next before-cursor
    break-unless next  # end of text
    nextc:char <- get *next, value:offset
    at-end-of-line?:bool <- equal nextc, 10/newline
    break-if at-end-of-line?
    cursor-column <- add cursor-column, 1
    at-right?:bool <- equal cursor-column, right
    break-if at-right?
    *editor <- put *editor, cursor-column:offset, cursor-column
    before-cursor <- copy next
    *editor <- put *editor, before-cursor:offset, before-cursor
    loop
  }
]

scenario editor-moves-to-end-of-line-with-ctrl-e-2 [
  local-scope
  assume-screen 10/width, 5/height
  s:text <- new [123
456]
  e:&:editor <- new-editor s, 0/left, 10/right
  editor-render screen, e
  $clear-trace
  # start on second line (no newline after), press ctrl-e
  assume-console [
    left-click 2, 1
    press ctrl-e
  ]
  run [
    editor-event-loop screen, console, e
    4:num/raw <- get *e, cursor-row:offset
    5:num/raw <- get *e, cursor-column:offset
  ]
  # cursor moves to end of line
  memory-should-contain [
    4 <- 2
    5 <- 3
  ]
  check-trace-count-for-label 0, [print-character]
]

scenario editor-moves-to-end-of-line-with-end [
  local-scope
  assume-screen 10/width, 5/height
  s:text <- new [123
456]
  e:&:editor <- new-editor s, 0/left, 10/right
  editor-render screen, e
  $clear-trace
  # start on first line, press 'end'
  assume-console [
    left-click 1, 1
    press end
  ]
  run [
    editor-event-loop screen, console, e
    3:num/raw <- get *e, cursor-row:offset
    4:num/raw <- get *e, cursor-column:offset
  ]
  # cursor moves to end of line
  memory-should-contain [
    3 <- 1
    4 <- 3
  ]
  check-trace-count-for-label 0, [print-character]
]

scenario editor-moves-to-end-of-line-with-end-2 [
  local-scope
  assume-screen 10/width, 5/height
  s:text <- new [123
456]
  e:&:editor <- new-editor s, 0/left, 10/right
  editor-render screen, e
  $clear-trace
  # start on second line (no newline after), press 'end'
  assume-console [
    left-click 2, 1
    press end
  ]
  run [
    editor-event-loop screen, console, e
    3:num/raw <- get *e, cursor-row:offset
    4:num/raw <- get *e, cursor-column:offset
  ]
  # cursor moves to end of line
  memory-should-contain [
    3 <- 2
    4 <- 3
  ]
  check-trace-count-for-label 0, [print-character]
]

scenario editor-moves-to-end-of-wrapped-line [
  local-scope
  assume-screen 10/width, 5/height
  s:text <- new [123456
789]
  e:&:editor <- new-editor s, 0/left, 5/right
  editor-render screen, e
  $clear-trace
  # start on first line, press 'end'
  assume-console [
    left-click 1, 1
    press end
  ]
  run [
    editor-event-loop screen, console, e
    10:num/raw <- get *e, cursor-row:offset
    11:num/raw <- get *e, cursor-column:offset
  ]
  # cursor moves to end of line
  memory-should-contain [
    10 <- 1
    11 <- 3
  ]
  # no prints
  check-trace-count-for-label 0, [print-character]
  # before-cursor is also consistent
  assume-console [
    type [a]
  ]
  run [
    editor-event-loop screen, console, e
  ]
  screen-should-contain [
    .          .
    .123a     .
    .456       .
    .789       .
    .┈┈┈┈┈     .
  ]
]

# ctrl-u - delete text from start of line until (but not at) cursor

scenario editor-deletes-to-start-of-line-with-ctrl-u [
  local-scope
  assume-screen 10/width, 5/height
  s:text <- new [123
456]
  e:&:editor <- new-editor s, 0/left, 10/right
  editor-render screen, e
  $clear-trace
  # start on second line, press ctrl-u
  assume-console [
    left-click 2, 2
    press ctrl-u
  ]
  run [
    editor-event-loop screen, console, e
  ]
  # cursor deletes to start of line
  screen-should-contain [
    .          .
    .123       .
    .6         .
    .┈┈┈┈┈┈┈┈┈┈.
    .          .
  ]
  check-trace-count-for-label 10, [print-character]
]

after <handle-special-character> [
  {
    delete-to-start-of-line?:bool <- equal c, 21/ctrl-u
    break-unless delete-to-start-of-line?
    <begin-delete-to-start-of-line>
    deleted-cells:&:duplex-list:char <- delete-to-start-of-line editor
    <end-delete-to-start-of-line>
    go-render?:bool <- minimal-render-for-ctrl-u screen, editor, deleted-cells
    return
  }
]

def minimal-render-for-ctrl-u screen:&:screen, editor:&:editor, deleted-cells:&:duplex-list:char -> go-render?:bool, screen:&:screen [
  local-scope
  load-inputs
  curr-column:num <- get *editor, cursor-column:offset
  # accumulate the current line as text and render it
  buf:&:buffer:char <- new-buffer 30  # accumulator for the text we need to render
  curr:&:duplex-list:char <- get *editor, before-cursor:offset
  i:num <- copy curr-column
  right:num <- get *editor, right:offset
  {
    # if we have a wrapped line, give up and render the whole screen
    wrap?:bool <- greater-or-equal i, right
    return-if wrap?, true/go-render
    curr <- next curr
    break-unless curr
    c:char <- get *curr, value:offset
    b:bool <- equal c, 10
    break-if b
    buf <- append buf, c
    i <- add i, 1
    loop
  }
  # if the line used to be wrapped, give up and render the whole screen
  num-deleted-cells:num <- length deleted-cells
  old-row-len:num <- add i, num-deleted-cells
  left:num <- get *editor, left:offset
  end:num <- subtract right, left
  wrap?:bool <- greater-or-equal old-row-len, end
  return-if wrap?, true/go-render
  curr-line:text <- buffer-to-array buf
  curr-row:num <- get *editor, cursor-row:offset
  render-code screen, curr-line, curr-column, right, curr-row
  return false/dont-render
]

def delete-to-start-of-line editor:&:editor -> result:&:duplex-list:char, editor:&:editor [
  local-scope
  load-inputs
  # compute range to delete
  init:&:duplex-list:char <- get *editor, data:offset
  before-cursor:&:duplex-list:char <- get *editor, before-cursor:offset
  start:&:duplex-list:char <- copy before-cursor
  end:&:duplex-list:char <- next before-cursor
  {
    at-start-of-text?:bool <- equal start, init
    break-if at-start-of-text?
    curr:char <- get *start, value:offset
    at-start-of-line?:bool <- equal curr, 10/newline
    break-if at-start-of-line?
    start <- prev start
    assert start, [delete-to-start-of-line tried to move before start of text]
    loop
  }
  # snip it out
  result:&:duplex-list:char <- next start
  remove-between start, end
  # adjust cursor
  before-cursor <- copy start
  *editor <- put *editor, before-cursor:offset, before-cursor
  left:num <- get *editor, left:offset
  *editor <- put *editor, cursor-column:offset, left
  # if the line wrapped before, we may need to adjust cursor-row as well
  right:num <- get *editor, right:offset
  width:num <- subtract right, left
  num-deleted:num <- length result
  cursor-row-adjustment:num <- divide-with-remainder num-deleted, width
  return-unless cursor-row-adjustment
  cursor-row:num <- get *editor, cursor-row:offset
  cursor-row <- subtract cursor-row, cursor-row-adjustment
  put *editor, cursor-row:offset, cursor-row
]

def render-code screen:&:screen, s:text, left:num, right:num, row:num -> row:num, screen:&:screen [
  local-scope
  load-inputs
  return-unless s
  color:num <- copy 7/white
  column:num <- copy left
  screen <- move-cursor screen, row, column
  screen-height:num <- screen-height screen
  i:num <- copy 0
  len:num <- length *s
  {
    +next-character
    done?:bool <- greater-or-equal i, len
    break-if done?
    done? <- greater-or-equal row, screen-height
    break-if done?
    c:char <- index *s, i
    <character-c-received>
    {
      # newline? move to left rather than 0
      newline?:bool <- equal c, 10/newline
      break-unless newline?
      # clear rest of line in this window
      {
        done?:bool <- greater-than column, right
        break-if done?
        space:char <- copy 32/space
        print screen, space
        column <- add column, 1
        loop
      }
      row <- add row, 1
      column <- copy left
      screen <- move-cursor screen, row, column
      i <- add i, 1
      loop +next-character
    }
    {
      # at right? wrap.
      at-right?:bool <- equal column, right
      break-unless at-right?
      # print wrap icon
      wrap-icon:char <- copy 8617/loop-back-to-left
      print screen, wrap-icon, 245/grey
      column <- copy left
      row <- add row, 1
      screen <- move-cursor screen, row, column
      # don't increment i
      loop +next-character
    }
    i <- add i, 1
    print screen, c, color
    column <- add column, 1
    loop
  }
  was-at-left?:bool <- equal column, left
  clear-line-until screen, right
  {
    break-if was-at-left?
    row <- add row, 1
  }
  move-cursor screen, row, left
]

scenario editor-deletes-to-start-of-line-with-ctrl-u-2 [
  local-scope
  assume-screen 10/width, 5/height
  s:text <- new [123
456]
  e:&:editor <- new-editor s, 0/left, 10/right
  editor-render screen, e
  $clear-trace
  # start on first line (no newline before), press ctrl-u
  assume-console [
    left-click 1, 2
    press ctrl-u
  ]
  run [
    editor-event-loop screen, console, e
  ]
  # cursor deletes to start of line
  screen-should-contain [
    .          .
    .3         .
    .456       .
    .┈┈┈┈┈┈┈┈┈┈.
    .          .
  ]
  check-trace-count-for-label 10, [print-character]
]

scenario editor-deletes-to-start-of-line-with-ctrl-u-3 [
  local-scope
  assume-screen 10/width, 5/height
  s:text <- new [123
456]
  e:&:editor <- new-editor s, 0/left, 10/right
  editor-render screen, e
  $clear-trace
  # start past end of line, press ctrl-u
  assume-console [
    left-click 1, 3
    press ctrl-u
  ]
  run [
    editor-event-loop screen, console, e
  ]
  # cursor deletes to start of line
  screen-should-contain [
    .          .
    .          .
    .456       .
    .┈┈┈┈┈┈┈┈┈┈.
    .          .
  ]
  check-trace-count-for-label 10, [print-character]
]

scenario editor-deletes-to-start-of-final-line-with-ctrl-u [
  local-scope
  assume-screen 10/width, 5/height
  s:text <- new [123
456]
  e:&:editor <- new-editor s, 0/left, 10/right
  editor-render screen, e
  $clear-trace
  # start past end of final line, press ctrl-u
  assume-console [
    left-click 2, 3
    press ctrl-u
  ]
  run [
    editor-event-loop screen, console, e
  ]
  # cursor deletes to start of line
  screen-should-contain [
    .          .
    .123       .
    .          .
    .┈┈┈┈┈┈┈┈┈┈.
    .          .
  ]
  check-trace-count-for-label 10, [print-character]
]

scenario editor-deletes-to-start-of-wrapped-line-with-ctrl-u [
  local-scope
  assume-screen 10/width, 10/height
  # first line starts out wrapping
  s:text <- new [123456
789]
  e:&:editor <- new-editor s, 0/left, 5/right
  editor-render screen, e
  screen-should-contain [
    .          .
    .1234     .
    .56        .
    .789       .
    .┈┈┈┈┈     .
    .          .
  ]
  $clear-trace
  # ctrl-u enough of the first line that it's no longer wrapping
  assume-console [
    left-click 1, 3
    press ctrl-u
  ]
  run [
    editor-event-loop screen, console, e
  ]
  # entire screen needs to be refreshed
  screen-should-contain [
    .          .
    .456       .
    .789       .
    .┈┈┈┈┈     .
    .          .
  ]
  check-trace-count-for-label 45, [print-character]
]

# sometimes hitting ctrl-u needs to adjust the cursor row
scenario editor-deletes-to-start-of-wrapped-line-with-ctrl-u-2 [
  local-scope
  assume-screen 10/width, 10/height
  # third line starts out wrapping
  s:text <- new [1
2
345678
9]
  e:&:editor <- new-editor s, 0/left, 5/right
  editor-render screen, e
  screen-should-contain [
    .          .
    .1         .
    .2         .
    .3456     .
    .78        .
    .9         .
    .┈┈┈┈┈     .
    .          .
  ]
  # position cursor on screen line after the wrap and hit ctrl-u
  assume-console [
    left-click 4, 1  # on '8'
    press ctrl-u
  ]
  run [
    editor-event-loop screen, console, e
    10:num/raw <- get *e, cursor-row:offset
    11:num/raw <- get *e, cursor-column:offset
  ]
  screen-should-contain [
    .          .
    .1         .
    .2         .
    .8         .
    .9         .
    .┈┈┈┈┈     .
    .          .
  ]
  # cursor moves up one screen line
  memory-should-contain [
    10 <- 3  # cursor-row
    11 <- 0  # cursor-column
  ]
]

# line wrapping twice (taking up 3 screen lines)
scenario editor-deletes-to-start-of-wrapped-line-with-ctrl-u-3 [
  local-scope
  assume-screen 10/width, 10/height
  # third line starts out wrapping
  s:text <- new [1
2
3456789abcd
e]
  e:&:editor <- new-editor s, 0/left, 5/right
  editor-render screen, e
  assume-console [
    left-click 4, 1  # on '8'
  ]
  editor-event-loop screen, console, e
  screen-should-contain [
    .          .
    .1         .
    .2         .
    .3456     .
    .789a     .
    .bcd       .
    .e         .
    .┈┈┈┈┈     .
    .          .
  ]
  assume-console [
    left-click 5, 1
    press ctrl-u
  ]
  run [
    editor-event-loop screen, console, e
    10:num/raw <- get *e, cursor-row:offset
    11:num/raw <- get *e, cursor-column:offset
  ]
  screen-should-contain [
    .          .
    .1         .
    .2         .
    .cd        .
    .e         .
    .┈┈┈┈┈     .
    .          .
  ]
  # make sure we adjusted cursor-row
  memory-should-contain [
    10 <- 3  # cursor-row
    11 <- 0  # cursor-column
  ]
]

# ctrl-k - delete text from cursor to end of line (but not the newline)

scenario editor-deletes-to-end-of-line-with-ctrl-k [
  local-scope
  assume-screen 10/width, 5/height
  s:text <- new [123
456]
  e:&:editor <- new-editor s, 0/left, 10/right
  editor-render screen, e
  $clear-trace
  # start on first line, press ctrl-k
  assume-console [
    left-click 1, 1
    press ctrl-k
  ]
  run [
    editor-event-loop screen, console, e
  ]
  # cursor deletes to end of line
  screen-should-contain [
    .          .
    .1         .
    .456       .
    .┈┈┈┈┈┈┈┈┈┈.
    .          .
  ]
  check-trace-count-for-label 9, [print-character]
]

after <handle-special-character> [
  {
    delete-to-end-of-line?:bool <- equal c, 11/ctrl-k
    break-unless delete-to-end-of-line?
    <begin-delete-to-end-of-line>
    deleted-cells:&:duplex-list:char <- delete-to-end-of-line editor
    <end-delete-to-end-of-line>
    # checks if we can do a minimal render and if we can it will do a minimal render
    go-render?:bool <- minimal-render-for-ctrl-k screen, editor, deleted-cells
    return
  }
]

def minimal-render-for-ctrl-k screen:&:screen, editor:&:editor, deleted-cells:&:duplex-list:char -> go-render?:bool, screen:&:screen [
  local-scope
  load-inputs
  # if we deleted nothing, there's nothing to render
  return-unless deleted-cells, false/dont-render
  # if the line used to wrap before, give up and render the whole screen
  curr-column:num <- get *editor, cursor-column:offset
  num-deleted-cells:num <- length deleted-cells
  old-row-len:num <- add curr-column, num-deleted-cells
  left:num <- get *editor, left:offset
  right:num <- get *editor, right:offset
  end:num <- subtract right, left
  wrap?:bool <- greater-or-equal old-row-len, end
  return-if wrap?, true/go-render
  clear-line-until screen, right
  return false/dont-render
]

def delete-to-end-of-line editor:&:editor -> result:&:duplex-list:char, editor:&:editor [
  local-scope
  load-inputs
  # compute range to delete
  start:&:duplex-list:char <- get *editor, before-cursor:offset
  end:&:duplex-list:char <- next start
  {
    at-end-of-text?:bool <- equal end, null
    break-if at-end-of-text?
    curr:char <- get *end, value:offset
    at-end-of-line?:bool <- equal curr, 10/newline
    break-if at-end-of-line?
    end <- next end
    loop
  }
  # snip it out
  result <- next start
  remove-between start, end
]

scenario editor-deletes-to-end-of-line-with-ctrl-k-2 [
  local-scope
  assume-screen 10/width, 5/height
  s:text <- new [123
456]
  e:&:editor <- new-editor s, 0/left, 10/right
  editor-render screen, e
  $clear-trace
  # start on second line (no newline after), press ctrl-k
  assume-console [
    left-click 2, 1
    press ctrl-k
  ]
  run [
    editor-event-loop screen, console, e
  ]
  # cursor deletes to end of line
  screen-should-contain [
    .          .
    .123       .
    .4         .
    .┈┈┈┈┈┈┈┈┈┈.
    .          .
  ]
  check-trace-count-for-label 9, [print-character]
]

scenario editor-deletes-to-end-of-line-with-ctrl-k-3 [
  local-scope
  assume-screen 10/width, 5/height
  s:text <- new [123
456]
  e:&:editor <- new-editor s, 0/left, 10/right
  editor-render screen, e
  $clear-trace
  # start at end of line
  assume-console [
    left-click 1, 2
    press ctrl-k
  ]
  run [
    editor-event-loop screen, console, e
  ]
  # cursor deletes just last character
  screen-should-contain [
    .          .
    .12        .
    .456       .
    .┈┈┈┈┈┈┈┈┈┈.
    .          .
  ]
  check-trace-count-for-label 8, [print-character]
]

scenario editor-deletes-to-end-of-line-with-ctrl-k-4 [
  local-scope
  assume-screen 10/width, 5/height
  s:text <- new [123
456]
  e:&:editor <- new-editor s, 0/left, 10/right
  editor-render screen, e
  $clear-trace
  # start past end of line
  assume-console [
    left-click 1, 3
    press ctrl-k
  ]
  run [
    editor-event-loop screen, console, e
  ]
  # cursor deletes nothing
  screen-should-contain [
    .          .
    .123       .
    .456       .
    .┈┈┈┈┈┈┈┈┈┈.
    .          .
  ]
  check-trace-count-for-label 7, [print-character]
]

scenario editor-deletes-to-end-of-line-with-ctrl-k-5 [
  local-scope
  assume-screen 10/width, 5/height
  s:text <- new [123
456]
  e:&:editor <- new-editor s, 0/left, 10/right
  editor-render screen, e
  $clear-trace
  # start at end of text
  assume-console [
    left-click 2, 2
    press ctrl-k
  ]
  run [
    editor-event-loop screen, console, e
  ]
  # cursor deletes just the final character
  screen-should-contain [
    .          .
    .123       .
    .45        .
    .┈┈┈┈┈┈┈┈┈┈.
    .          .
  ]
  check-trace-count-for-label 8, [print-character]
]

scenario editor-deletes-to-end-of-line-with-ctrl-k-6 [
  local-scope
  assume-screen 10/width, 5/height
  s:text <- new [123
456]
  e:&:editor <- new-editor s, 0/left, 10/right
  editor-render screen, e
  $clear-trace
  # start past end of text
  assume-console [
    left-click 2, 3
    press ctrl-k
  ]
  run [
    editor-event-loop screen, console, e
  ]
  # cursor deletes nothing
  screen-should-contain [
    .          .
    .123       .
    .456       .
    .┈┈┈┈┈┈┈┈┈┈.
    .          .
  ]
  # no prints necessary
  check-trace-count-for-label 0, [print-character]
]

scenario editor-deletes-to-end-of-wrapped-line-with-ctrl-k [
  local-scope
  assume-screen 10/width, 5/height
  # create an editor with the first line wrapping to a second screen row
  s:text <- new [1234
567]
  e:&:editor <- new-editor s, 0/left, 4/right
  editor-render screen, e
  $clear-trace
  # delete all of the first wrapped line
  assume-console [
    press ctrl-k
  ]
  run [
    editor-event-loop screen, console, e
  ]
  # screen shows an empty unwrapped first line
  screen-should-contain [
    .          .
    .          .
    .567       .
    .┈┈┈┈      .
    .          .
  ]
  # entire screen is refreshed
  check-trace-count-for-label 16, [print-character]
]

# takes a pointer into the doubly-linked list, scans ahead at most 'max'
# positions until the next newline
# returns original if no next newline
# beware: never return null pointer.
def before-start-of-next-line original:&:duplex-list:char, max:num -> curr:&:duplex-list:char [
  local-scope
  load-inputs
  count:num <- copy 0
  curr:&:duplex-list:char <- copy original
  # skip the initial newline if it exists
  {
    c:char <- get *curr, value:offset
    at-newline?:bool <- equal c, 10/newline
    break-unless at-newline?
    curr <- next curr
    count <- add count, 1
  }
  {
    return-unless curr, original
    done?:bool <- greater-or-equal count, max
    break-if done?
    c:char <- get *curr, value:offset
    at-newline?:bool <- equal c, 10/newline
    break-if at-newline?
    curr <- next curr
    count <- add count, 1
    loop
  }
  return-unless curr, original
  return curr
]

# ctrl-/ - comment/uncomment current line

after <handle-special-character> [
  {
    comment-toggle?:bool <- equal c, 31/ctrl-slash
    break-unless comment-toggle?
    cursor-column:num <- get *editor, cursor-column:offset
    data:&:duplex-list:char <- get *editor, data:offset
    <begin-insert-character>
    before-line-start:&:duplex-list:char <- before-start-of-screen-line editor
    line-start:&:duplex-list:char <- next before-line-start
    commented-out?:bool <- match line-start, [#? ]  # comment prefix
    {
      break-unless commented-out?
      # uncomment
      data <- remove line-start, 3/length-comment-prefix, data
      cursor-column <- subtract cursor-column, 3/length-comment-prefix
      *editor <- put *editor, cursor-column:offset, cursor-column
      go-render? <- render-line-from-start screen, editor, 3/size-of-comment-leader
    }
    {
      break-if commented-out?
      # comment
      insert before-line-start, [#? ]
      cursor-column <- add cursor-column, 3/length-comment-prefix
      *editor <- put *editor, cursor-column:offset, cursor-column
      go-render? <- render-line-from-start screen, editor, 0
    }
    <end-insert-character>
    return
  }
]

# Render just from the start of the current line, and only if it wasn't
# wrapping before (include margin) and isn't wrapping now. Otherwise just tell
# the caller to go-render? the entire screen.
def render-line-from-start screen:&:screen, editor:&:editor, right-margin:num -> go-render?:bool, screen:&:screen [
  local-scope
  load-inputs
  before-line-start:&:duplex-list:char <- before-start-of-screen-line editor
  line-start:&:duplex-list:char <- next before-line-start
  color:num <- copy 7/white
  left:num <- get *editor, left:offset
  cursor-row:num <- get *editor, cursor-row:offset
  screen <- move-cursor screen, cursor-row, left
  right:num <- get *editor, right:offset
  end:num <- subtract right, right-margin
  i:num <- copy 0
  curr:&:duplex-list:char <- copy line-start
  {
    render-all?:bool <- greater-or-equal i, end
    return-if render-all?, true/go-render
    break-unless curr
    c:char <- get *curr, value:offset
    newline?:bool <- equal c, 10/newline
    break-if newline?
    color <- get-color color, c
    print screen, c, color
    curr <- next curr
    i <- add i, 1
    loop
  }
  clear-line-until screen, right
  return false/dont-render
]

def before-start-of-screen-line editor:&:editor -> result:&:duplex-list:char [
  local-scope
  load-inputs
  cursor:&:duplex-list:char <- get *editor, before-cursor:offset
  {
    next:&:duplex-list:char <- next cursor
    break-unless next
    cursor <- copy next
  }
  result <- before-previous-screen-line cursor, editor
]

scenario editor-comments-empty-line [
  local-scope
  assume-screen 10/width, 5/height
  e:&:editor <- new-editor [], 0/left, 5/right
  editor-render screen, e
  $clear-trace
  assume-console [
    press ctrl-slash
  ]
  run [
    editor-event-loop screen, console, e
    4:num/raw <- get *e, cursor-row:offset
    5:num/raw <- get *e, cursor-column:offset
  ]
  screen-should-contain [
    .          .
    .#?        .
    .┈┈┈┈┈     .
    .          .
  ]
  memory-should-contain [
    4 <- 1
    5 <- 3
  ]
  check-trace-count-for-label 5, [print-character]
]

scenario editor-comments-at-start-of-contents [
  local-scope
  assume-screen 10/width, 5/height
  e:&:editor <- new-editor [ab], 0/left, 10/right
  editor-render screen, e
  $clear-trace
  assume-console [
    press ctrl-slash
  ]
  run [
    editor-event-loop screen, console, e
    4:num/raw <- get *e, cursor-row:offset
    5:num/raw <- get *e, cursor-column:offset
  ]
  screen-should-contain [
    .          .
    .#? ab     .
    .┈┈┈┈┈┈┈┈┈┈.
    .          .
  ]
  memory-should-contain [
    4 <- 1
    5 <- 3
  ]
  check-trace-count-for-label 10, [print-character]
]

scenario editor-comments-at-end-of-contents [
  local-scope
  assume-screen 10/width, 5/height
  e:&:editor <- new-editor [ab], 0/left, 10/right
  editor-render screen, e
  $clear-trace
  assume-console [
    left-click 1, 7
    press ctrl-slash
  ]
  run [
    editor-event-loop screen, console, e
    4:num/raw <- get *e, cursor-row:offset
    5:num/raw <- get *e, cursor-column:offset
  ]
  screen-should-contain [
    .          .
    .#? ab     .
    .┈┈┈┈┈┈┈┈┈┈.
    .          .
  ]
  memory-should-contain [
    4 <- 1
    5 <- 5
  ]
  check-trace-count-for-label 10, [print-character]
  # toggle to uncomment
  $clear-trace
  assume-console [
    press ctrl-slash
  ]
  run [
    editor-event-loop screen, console, e
    4:num/raw <- get *e, cursor-row:offset
    5:num/raw <- get *e, cursor-column:offset
  ]
  screen-should-contain [
    .          .
    .ab        .
    .┈┈┈┈┈┈┈┈┈┈.
    .          .
  ]
  check-trace-count-for-label 10, [print-character]
]

scenario editor-comments-almost-wrapping-line [
  local-scope
  assume-screen 10/width, 5/height
  # editor starts out with a non-wrapping line
  e:&:editor <- new-editor [abcd], 0/left, 5/right
  editor-render screen, e
  screen-should-contain [
    .          .
    .abcd      .
    .┈┈┈┈┈     .
    .          .
  ]
  $clear-trace
  # on commenting the line is now wrapped
  assume-console [
    left-click 1, 7
    press ctrl-slash
  ]
  run [
    editor-event-loop screen, console, e
  ]
  screen-should-contain [
    .          .
    .#? a     .
    .bcd       .
    .┈┈┈┈┈     .
    .          .
  ]
]

scenario editor-uncomments-just-wrapping-line [
  local-scope
  assume-screen 10/width, 5/height
  # editor starts out with a comment that wraps the line
  e:&:editor <- new-editor [#? ab], 0/left, 5/right
  editor-render screen, e
  screen-should-contain [
    .          .
    .#? a     .
    .b         .
    .┈┈┈┈┈     .
    .          .
  ]
  $clear-trace
  # on uncommenting the line is no longer wrapped
  assume-console [
    left-click 1, 7
    press ctrl-slash
  ]
  run [
    editor-event-loop screen, console, e
  ]
  screen-should-contain [
    .          .
    .ab        .
    .┈┈┈┈┈     .
    .          .
  ]
]