about summary refs log tree commit diff stats
path: root/081print.mu
blob: 2c2e09ae44a8fab8a2c3afe855f6c0a7a58f6b28 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
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
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
# Wrappers around print primitives that take a 'screen' object and are thus
# easier to test.

container screen [
  num-rows:num
  num-columns:num
  cursor-row:num
  cursor-column:num
  data:&:@:screen-cell  # capacity num-rows*num-columns
  top-idx:num  # index inside data that corresponds to top-left of screen
               # modified on scroll, wrapping around to the top of data
]

container screen-cell [
  contents:char
  color:num
]

def new-fake-screen w:num, h:num -> result:&:screen [
  local-scope
  load-ingredients
  result <- new screen:type
  non-zero-width?:bool <- greater-than w, 0
  assert non-zero-width?, [screen can't have zero width]
  non-zero-height?:bool <- greater-than h, 0
  assert non-zero-height?, [screen can't have zero height]
  bufsize:num <- multiply w, h
  data:&:@:screen-cell <- new screen-cell:type, bufsize
  *result <- merge h/num-rows, w/num-columns, 0/cursor-row, 0/cursor-column, data, 0/top-idx
  result <- clear-screen result
]

def clear-screen screen:&:screen -> screen:&:screen [
  local-scope
  load-ingredients
  {
    break-if screen
    # real screen
    clear-display
    return
  }
  # fake screen
  buf:&:@:screen-cell <- get *screen, data:offset
  max:num <- length *buf
  i:num <- copy 0
  {
    done?:bool <- greater-or-equal i, max
    break-if done?
    curr:screen-cell <- merge 0/empty, 7/white
    *buf <- put-index *buf, i, curr
    i <- add i, 1
    loop
  }
  # reset cursor
  *screen <- put *screen, cursor-row:offset, 0
  *screen <- put *screen, cursor-column:offset, 0
  *screen <- put *screen, top-idx:offset, 0
]

def fake-screen-is-empty? screen:&:screen -> result:bool [
  local-scope
  load-ingredients
  return-unless screen, 1/true  # do nothing for real screens
  buf:&:@:screen-cell <- get *screen, data:offset
  i:num <- copy 0
  len:num <- length *buf
  {
    done?:bool <- greater-or-equal i, len
    break-if done?
    curr:screen-cell <- index *buf, i
    curr-contents:char <- get curr, contents:offset
    i <- add i, 1
    loop-unless curr-contents
    # not 0
    return 0/false
  }
  return 1/true
]

def print screen:&:screen, c:char -> screen:&:screen [
  local-scope
  load-ingredients
  color:num, color-found?:bool <- next-ingredient
  {
    # default color to white
    break-if color-found?
    color <- copy 7/white
  }
  bg-color:num, bg-color-found?:bool <- next-ingredient
  {
    # default bg-color to black
    break-if bg-color-found?
    bg-color <- copy 0/black
  }
  c2:num <- character-to-code c
  trace 90, [print-character], c2
  {
    # real screen
    break-if screen
    print-character-to-display c, color, bg-color
    return
  }
  # fake screen
  # (handle special cases exactly like in the real screen)
  width:num <- get *screen, num-columns:offset
  height:num <- get *screen, num-rows:offset
  capacity:num <- multiply width, height
  row:num <- get *screen, cursor-row:offset
  column:num <- get *screen, cursor-column:offset
  buf:&:@:screen-cell <- get *screen, data:offset
  # some potentially slow sanity checks for preconditions {
  # eliminate fractions from column and row
  row <- round row
  column <- round column
  # if cursor is past left margin (error), reset to left margin
  {
    too-far-left?:bool <- lesser-than column, 0
    break-unless too-far-left?
    column <- copy 0
    *screen <- put *screen, cursor-column:offset, column
  }
  # if cursor is at right margin, wrap
  {
    at-right?:bool <- equal column, width
    break-unless at-right?
    column <- copy 0
    *screen <- put *screen, cursor-column:offset, column
    row <- add row, 1
    *screen <- put *screen, cursor-row:offset, row
  }
  # if cursor is past right margin (error), reset to right margin
  {
    too-far-right?:bool <- greater-than column, width
    break-unless too-far-right?
    column <- subtract width, 1
    *screen <- put *screen, cursor-row:offset, row
  }
  # if row is above top margin (error), reset to top margin
  {
    too-far-up?:bool <- lesser-than row, 0
    break-unless too-far-up?
    row <- copy 0
    *screen <- put *screen, cursor-row:offset, row
  }
  # if row is at bottom margin, scroll
  {
    at-bottom?:bool <- equal row, height
    break-unless at-bottom?
    scroll-fake-screen screen
    row <- subtract height, 1
    *screen <- put *screen, cursor-row:offset, row
  }
  # if row is below bottom margin (error), reset to bottom margin
  {
    too-far-down?:bool <- greater-than row, height
    break-unless too-far-down?
    row <- subtract height, 1
    *screen <- put *screen, cursor-row:offset, row
  }
  # }
#?     $print [print-character (], row, [, ], column, [): ], c, 10/newline
  # special-case: newline
  {
    newline?:bool <- equal c, 10/newline
    break-unless newline?
    cursor-down-on-fake-screen screen  # doesn't modify column
    return
  }
  # special-case: linefeed
  {
    linefeed?:bool <- equal c, 13/linefeed
    break-unless linefeed?
    *screen <- put *screen, cursor-column:offset, 0
    return
  }
  # special-case: backspace
  # moves cursor left but does not erase
  {
    backspace?:bool <- equal c, 8/backspace
    break-unless backspace?
    {
      break-unless column
      column <- subtract column, 1
      *screen <- put *screen, cursor-column:offset, column
    }
    return
  }
  # save character in fake screen
  top-idx:num <- get *screen, top-idx:offset
  index:num <- data-index row, column, width, height, top-idx
  cursor:screen-cell <- merge c, color
  *buf <- put-index *buf, index, cursor
  # move cursor to next character
  # (but don't bother making it valid; we'll do that before the next print)
  column <- add column, 1
  *screen <- put *screen, cursor-column:offset, column
]

def cursor-down-on-fake-screen screen:&:screen -> screen:&:screen [
  local-scope
  load-ingredients
  row:num <- get *screen, cursor-row:offset
  height:num <- get *screen, num-rows:offset
  bottom:num <- subtract height, 1
  at-bottom?:bool <- greater-or-equal row, bottom
  {
    break-if at-bottom?
    row <- add row, 1
    *screen <- put *screen, cursor-row:offset, row
  }
  {
    break-unless at-bottom?
    scroll-fake-screen screen  # does not modify row
  }
]

def scroll-fake-screen screen:&:screen -> screen:&:screen [
  local-scope
  load-ingredients
  width:num <- get *screen, num-columns:offset
  height:num <- get *screen, num-rows:offset
  buf:&:@:screen-cell <- get *screen, data:offset
  # clear top line and 'rotate' it to the bottom
  top-idx:num <- get *screen, top-idx:offset  # 0 <= top-idx < len(buf)
  next-top-idx:num <- add top-idx, width  # 0 <= next-top-idx <= len(buf)
  empty-cell:screen-cell <- merge 0, 0
  {
    done?:bool <- greater-or-equal top-idx, next-top-idx
    break-if done?
    put-index *buf, top-idx, empty-cell
    top-idx <- add top-idx, 1
    # no modulo; top-idx is always a multiple of width,
    # so it can never wrap around inside this loop
    loop
  }
  # top-idx now same as next-top-idx; wrap around if necessary
  capacity:num <- multiply width, height
  _, top-idx <- divide-with-remainder, top-idx, capacity
  *screen <- put *screen, top-idx:offset, top-idx
]

# translate from screen (row, column) coordinates to an index into data
# while accounting for scrolling (sliding top-idx)
def data-index row:num, column:num, width:num, height:num, top-idx:num -> result:num [
  local-scope
  load-ingredients
  result <- multiply width, row
  result <- add result, column, top-idx
  capacity:num <- multiply width, height
  _, result <- divide-with-remainder result, capacity
]

scenario print-character-at-top-left [
  local-scope
  fake-screen:&:screen <- new-fake-screen 3/width, 2/height
  run [
    a:char <- copy 97/a
    fake-screen <- print fake-screen, a:char
    cell:&:@:screen-cell <- get *fake-screen, data:offset
    1:@:screen-cell/raw <- copy *cell
  ]
  memory-should-contain [
    1 <- 6  # width*height
    2 <- 97  # 'a'
    3 <- 7  # white
    # rest of screen is empty
    4 <- 0
  ]
]

scenario print-character-at-fractional-coordinate [
  local-scope
  fake-screen:&:screen <- new-fake-screen 3/width, 2/height
  a:char <- copy 97/a
  run [
    move-cursor fake-screen, 0.5, 0
    fake-screen <- print fake-screen, a:char
    cell:&:@:screen-cell <- get *fake-screen, data:offset
    1:@:screen-cell/raw <- copy *cell
  ]
  memory-should-contain [
    1 <- 6  # width*height
    2 <- 97  # 'a'
    3 <- 7  # white
    # rest of screen is empty
    4 <- 0
  ]
]

scenario print-character-in-color [
  local-scope
  fake-screen:&:screen <- new-fake-screen 3/width, 2/height
  run [
    a:char <- copy 97/a
    fake-screen <- print fake-screen, a:char, 1/red
    cell:&:@:screen-cell <- get *fake-screen, data:offset
    1:@:screen-cell/raw <- copy *cell
  ]
  memory-should-contain [
    1 <- 6  # width*height
    2 <- 97  # 'a'
    3 <- 1  # red
    # rest of screen is empty
    4 <- 0
  ]
]

scenario print-backspace-character [
  local-scope
  fake-screen:&:screen <- new-fake-screen 3/width, 2/height
  a:char <- copy 97/a
  fake-screen <- print fake-screen, a
  run [
    backspace:char <- copy 8/backspace
    fake-screen <- print fake-screen, backspace
    10:num/raw <- get *fake-screen, cursor-column:offset
    cell:&:@:screen-cell <- get *fake-screen, data:offset
    11:@:screen-cell/raw <- copy *cell
  ]
  memory-should-contain [
    10 <- 0  # cursor column
    11 <- 6  # width*height
    12 <- 97  # still 'a'
    13 <- 7  # white
    # rest of screen is empty
    14 <- 0
  ]
]

scenario print-extra-backspace-character [
  local-scope
  fake-screen:&:screen <- new-fake-screen 3/width, 2/height
  a:char <- copy 97/a
  fake-screen <- print fake-screen, a
  run [
    backspace:char <- copy 8/backspace
    fake-screen <- print fake-screen, backspace
    fake-screen <- print fake-screen, backspace  # cursor already at left margin
    1:num/raw <- get *fake-screen, cursor-column:offset
    cell:&:@:screen-cell <- get *fake-screen, data:offset
    3:@:screen-cell/raw <- copy *cell
  ]
  memory-should-contain [
    1 <- 0  # cursor column
    3 <- 6  # width*height
    4 <- 97  # still 'a'
    5 <- 7  # white
    # rest of screen is empty
    6 <- 0
  ]
]

scenario print-character-at-right-margin [
  # fill top row of screen with text
  local-scope
  fake-screen:&:screen <- new-fake-screen 2/width, 2/height
  a:char <- copy 97/a
  fake-screen <- print fake-screen, a
  b:char <- copy 98/b
  fake-screen <- print fake-screen, b
  run [
    # cursor now at next row
    c:char <- copy 99/c
    fake-screen <- print fake-screen, c
    10:num/raw <- get *fake-screen, cursor-row:offset
    11:num/raw <- get *fake-screen, cursor-column:offset
    cell:&:@:screen-cell <- get *fake-screen, data:offset
    12:@:screen-cell/raw <- copy *cell
  ]
  memory-should-contain [
    10 <- 1  # cursor row
    11 <- 1  # cursor column
    12 <- 4  # width*height
    13 <- 97  # 'a'
    14 <- 7  # white
    15 <- 98  # 'b'
    16 <- 7  # white
    17 <- 99  # 'c'
    18 <- 7  # white
    19 <- 0  # ' '
    20 <- 7  # white
  ]
]

scenario print-newline-character [
  local-scope
  fake-screen:&:screen <- new-fake-screen 3/width, 2/height
  a:char <- copy 97/a
  fake-screen <- print fake-screen, a
  run [
    newline:char <- copy 10/newline
    fake-screen <- print fake-screen, newline
    10:num/raw <- get *fake-screen, cursor-row:offset
    11:num/raw <- get *fake-screen, cursor-column:offset
    cell:&:@:screen-cell <- get *fake-screen, data:offset
    12:@:screen-cell/raw <- copy *cell
  ]
  memory-should-contain [
    10 <- 1  # cursor row
    11 <- 1  # cursor column
    12 <- 6  # width*height
    13 <- 97  # 'a'
    14 <- 7  # white
    # rest of screen is empty
    15 <- 0
  ]
]

scenario print-newline-at-bottom-line [
  local-scope
  fake-screen:&:screen <- new-fake-screen 3/width, 2/height
  newline:char <- copy 10/newline
  fake-screen <- print fake-screen, newline
  fake-screen <- print fake-screen, newline
  run [
    # cursor now at bottom of screen
    fake-screen <- print fake-screen, newline
    10:num/raw <- get *fake-screen, cursor-row:offset
    11:num/raw <- get *fake-screen, cursor-column:offset
  ]
  # doesn't move further down
  memory-should-contain [
    10 <- 1  # cursor row
    11 <- 0  # cursor column
  ]
]

scenario print-character-at-bottom-right [
  local-scope
  fake-screen:&:screen <- new-fake-screen 2/width, 2/height
  a:char <- copy 97/a
  fake-screen <- print fake-screen, a
  b:char <- copy 98/b
  fake-screen <- print fake-screen, b
  c:char <- copy 99/c
  fake-screen <- print fake-screen, c
  run [
    # cursor now at bottom right
    d:char <- copy 100/d
    fake-screen <- print fake-screen, d
    10:num/raw <- get *fake-screen, cursor-row:offset
    11:num/raw <- get *fake-screen, cursor-column:offset
    12:num/raw <- get *fake-screen, top-idx:offset
    cell:&:@:screen-cell <- get *fake-screen, data:offset
    20:@:screen-cell/raw <- copy *cell
  ]
  # cursor column overflows the screen but is not wrapped yet
  memory-should-contain [
    10 <- 1  # cursor row
    11 <- 2  # cursor column -- outside screen
    12 <- 0  # top-idx -- not yet scrolled
    20 <- 4  # screen size (width*height)
    21 <- 97  # 'a'
    22 <- 7  # white
    23 <- 98  # 'b'
    24 <- 7  # white
    25 <- 99 # 'c'
    26 <- 7  # white
    27 <- 100  # 'd'
    28 <- 7  # white
  ]
  run [
    e:char <- copy 101/e
    print fake-screen, e
    10:num/raw <- get *fake-screen, cursor-row:offset
    11:num/raw <- get *fake-screen, cursor-column:offset
    12:num/raw <- get *fake-screen, top-idx:offset
    cell:&:@:screen-cell <- get *fake-screen, data:offset
    20:@:screen-cell/raw <- copy *cell
  ]
  memory-should-contain [
    # text scrolls by 1, we lose the top line
    10 <- 1  # cursor row
    11 <- 1  # cursor column -- wrapped
    12 <- 2  # top-idx -- scrolled
    20 <- 4  # screen size (width*height)
    # screen now checked in rotated order
    25 <- 99 # 'c'
    26 <- 7  # white
    27 <- 100  # 'd'
    28 <- 7  # white
    # screen wraps; bottom line is cleared of old contents
    21 <- 101  # 'e'
    22 <- 7  # white
    23 <- 0  # unused
    24 <- 0  # no color
  ]
]

# even though our screen supports scrolling, some apps may want to avoid
# scrolling
# these helpers help check for scrolling at development time
def save-top-idx screen:&:screen -> result:num [
  local-scope
  load-ingredients
  return-unless screen, 0  # check is only for fake screens
  result <- get *screen, top-idx:offset
]
def assert-no-scroll screen:&:screen, old-top-idx:num [
  local-scope
  load-ingredients
  return-unless screen
  new-top-idx:num <- get *screen, top-idx:offset
  no-scroll?:bool <- equal old-top-idx, new-top-idx
  assert no-scroll?, [render should never use screen's scrolling capabilities]
]

def clear-line screen:&:screen -> screen:&:screen [
  local-scope
  load-ingredients
  space:char <- copy 0/nul
  {
    break-if screen
    # real screen
    clear-line-on-display
    return
  }
  # fake screen
  width:num <- get *screen, num-columns:offset
  column:num <- get *screen, cursor-column:offset
  original-column:num <- copy column
  # space over the entire line
  {
    right:num <- subtract width, 1
    done?:bool <- greater-or-equal column, right
    break-if done?
    print screen, space
    column <- add column, 1
    loop
  }
  # now back to where the cursor was
  *screen <- put *screen, cursor-column:offset, original-column
]

# only for non-scrolling apps
def clear-line-until screen:&:screen, right:num/inclusive -> screen:&:screen [
  local-scope
  load-ingredients
  row:num, column:num <- cursor-position screen
  height:num <- screen-height screen
  past-bottom?:bool <- greater-or-equal row, height
  return-if past-bottom?
  space:char <- copy 32/space
  bg-color:num, bg-color-found?:bool <- next-ingredient
  {
    # default bg-color to black
    break-if bg-color-found?
    bg-color <- copy 0/black
  }
  {
    done?:bool <- greater-than column, right
    break-if done?
    screen <- print screen, space, 7/white, bg-color  # foreground color is mostly unused except if the cursor shows up at this cell
    column <- add column, 1
    loop
  }
]

def cursor-position screen:&:screen -> row:num, column:num [
  local-scope
  load-ingredients
  {
    break-if screen
    # real screen
    row, column <- cursor-position-on-display
    return
  }
  # fake screen
  row:num <- get *screen, cursor-row:offset
  column:num <- get *screen, cursor-column:offset
]

def move-cursor screen:&:screen, new-row:num, new-column:num -> screen:&:screen [
  local-scope
  load-ingredients
  {
    break-if screen
    # real screen
    move-cursor-on-display new-row, new-column
    return
  }
  # fake screen
  *screen <- put *screen, cursor-row:offset, new-row
  *screen <- put *screen, cursor-column:offset, new-column
]

scenario clear-line-erases-printed-characters [
  local-scope
  fake-screen:&:screen <- new-fake-screen 3/width, 2/height
  # print a character
  a:char <- copy 97/a
  fake-screen <- print fake-screen, a
  # move cursor to start of line
  fake-screen <- move-cursor fake-screen, 0/row, 0/column
  run [
    fake-screen <- clear-line fake-screen
    cell:&:@:screen-cell <- get *fake-screen, data:offset
    10:@:screen-cell/raw <- copy *cell
  ]
  # screen should be blank
  memory-should-contain [
    10 <- 6  # width*height
    11 <- 0
    12 <- 7
    13 <- 0
    14 <- 7
    15 <- 0
    16 <- 7
    17 <- 0
    18 <- 7
    19 <- 0
    20 <- 7
    21 <- 0
    22 <- 7
  ]
]

def cursor-down screen:&:screen -> screen:&:screen [
  local-scope
  load-ingredients
  {
    break-if screen
    # real screen
    move-cursor-down-on-display
    return
  }
  # fake screen
  height:num <- get *screen, num-rows:offset
  row:num <- get *screen, cursor-row:offset
  max:num <- subtract height, 1
  at-bottom?:bool <- greater-or-equal row, max
  return-if at-bottom?
  row <- add row, 1
  *screen <- put *screen, cursor-row:offset, row
]

def cursor-up screen:&:screen -> screen:&:screen [
  local-scope
  load-ingredients
  {
    break-if screen
    # real screen
    move-cursor-up-on-display
    return
  }
  # fake screen
  row:num <- get *screen, cursor-row:offset
  at-top?:bool <- lesser-or-equal row, 0
  return-if at-top?
  row <- subtract row, 1
  *screen <- put *screen, cursor-row:offset, row
]

def cursor-right screen:&:screen -> screen:&:screen [
  local-scope
  load-ingredients
  {
    break-if screen
    # real screen
    move-cursor-right-on-display
    return
  }
  # fake screen
  width:num <- get *screen, num-columns:offset
  column:num <- get *screen, cursor-column:offset
  max:num <- subtract width, 1
  at-bottom?:bool <- greater-or-equal column, max
  return-if at-bottom?
  column <- add column, 1
  *screen <- put *screen, cursor-column:offset, column
]

def cursor-left screen:&:screen -> screen:&:screen [
  local-scope
  load-ingredients
  {
    break-if screen
    # real screen
    move-cursor-left-on-display
    return
  }
  # fake screen
  column:num <- get *screen, cursor-column:offset
  at-top?:bool <- lesser-or-equal column, 0
  return-if at-top?
  column <- subtract column, 1
  *screen <- put *screen, cursor-column:offset, column
]

def cursor-to-start-of-line screen:&:screen -> screen:&:screen [
  local-scope
  load-ingredients
  row:num <- cursor-position screen
  column:num <- copy 0
  screen <- move-cursor screen, row, column
]

def cursor-to-next-line screen:&:screen -> screen:&:screen [
  local-scope
  load-ingredients
  screen <- cursor-down screen
  screen <- cursor-to-start-of-line screen
]

def move-cursor-to-column screen:&:screen, column:num -> screen:&:screen [
  local-scope
  load-ingredients
  row:num, _ <- cursor-position screen
  move-cursor screen, row, column
]

def screen-width screen:&:screen -> width:num [
  local-scope
  load-ingredients
  {
    break-unless screen
    # fake screen
    width <- get *screen, num-columns:offset
    return
  }
  # real screen
  width <- display-width
]

def screen-height screen:&:screen -> height:num [
  local-scope
  load-ingredients
  {
    break-unless screen
    # fake screen
    height <- get *screen, num-rows:offset
    return
  }
  # real screen
  height <- display-height
]

def print screen:&:screen, s:text -> screen:&:screen [
  local-scope
  load-ingredients
  color:num, color-found?:bool <- next-ingredient
  {
    # default color to white
    break-if color-found?
    color <- copy 7/white
  }
  bg-color:num, bg-color-found?:bool <- next-ingredient
  {
    # default bg-color to black
    break-if bg-color-found?
    bg-color <- copy 0/black
  }
  len:num <- length *s
  i:num <- copy 0
  {
    done?:bool <- greater-or-equal i, len
    break-if done?
    c:char <- index *s, i
    print screen, c, color, bg-color
    i <- add i, 1
    loop
  }
]

scenario print-text-wraps-past-right-margin [
  local-scope
  fake-screen:&:screen <- new-fake-screen 3/width, 2/height
  run [
    fake-screen <- print fake-screen, [abcd]
    5:num/raw <- get *fake-screen, cursor-row:offset
    6:num/raw <- get *fake-screen, cursor-column:offset
    7:num/raw <- get *fake-screen, top-idx:offset
    cell:&:@:screen-cell <- get *fake-screen, data:offset
    10:@:screen-cell/raw <- copy *cell
  ]
  memory-should-contain [
    5 <- 1  # cursor-row
    6 <- 1  # cursor-column
    7 <- 0  # top-idx
    10 <- 6  # width*height
    11 <- 97  # 'a'
    12 <- 7  # white
    13 <- 98  # 'b'
    14 <- 7  # white
    15 <- 99  # 'c'
    16 <- 7  # white
    17 <- 100  # 'd'
    18 <- 7  # white
    # rest of screen is empty
    19 <- 0
  ]
]

def print screen:&:screen, n:num -> screen:&:screen [
  local-scope
  load-ingredients
  color:num, color-found?:bool <- next-ingredient
  {
    # default color to white
    break-if color-found?
    color <- copy 7/white
  }
  bg-color:num, bg-color-found?:bool <- next-ingredient
  {
    # default bg-color to black
    break-if bg-color-found?
    bg-color <- copy 0/black
  }
  # todo: other bases besides decimal
  s:text <- to-text n
  screen <- print screen, s, color, bg-color
]

def print screen:&:screen, n:bool -> screen:&:screen [
  local-scope
  load-ingredients
  color:num, color-found?:bool <- next-ingredient
  {
    # default color to white
    break-if color-found?
    color <- copy 7/white
  }
  bg-color:num, bg-color-found?:bool <- next-ingredient
  {
    # default bg-color to black
    break-if bg-color-found?
    bg-color <- copy 0/black
  }
  n2:num <- copy n
  screen <- print screen, n2, color, bg-color
]

def print screen:&:screen, n:&:_elem -> screen:&:screen [
  local-scope
  load-ingredients
  color:num, color-found?:bool <- next-ingredient
  {
    # default color to white
    break-if color-found?
    color <- copy 7/white
  }
  bg-color:num, bg-color-found?:bool <- next-ingredient
  {
    # default bg-color to black
    break-if bg-color-found?
    bg-color <- copy 0/black
  }
  n2:num <- copy n
  screen <- print screen, n2, color, bg-color
]