about summary refs log tree commit diff stats
path: root/064list.mu
blob: d669ec2c9568cc2da4cee8c65be35a95352b38d1 (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
# A list links up multiple objects together to make them easier to manage.
#
# The objects must be of the same type. If you want to store multiple types in
# a single list, use an exclusive-container.

container list:_elem [
  value:_elem
  next:&:list:_elem
]

def push x:_elem, l:&:list:_elem -> result:&:list:_elem/contained-in:l [
  local-scope
  load-inputs
  result <- new {(list _elem): type}
  *result <- merge x, l
]

def first in:&:list:_elem -> result:_elem [
  local-scope
  load-inputs
  result <- get *in, value:offset
]

def rest in:&:list:_elem -> result:&:list:_elem/contained-in:in [
  local-scope
  load-inputs
  result <- get *in, next:offset
]

scenario list-handling [
  run [
    local-scope
    x:&:list:num <- push 3, null
    x <- push 4, x
    x <- push 5, x
    10:num/raw <- first x
    x <- rest x
    11:num/raw <- first x
    x <- rest x
    12:num/raw <- first x
    20:&:list:num/raw <- rest x
  ]
  memory-should-contain [
    10 <- 5
    11 <- 4
    12 <- 3
    20 <- 0  # nothing left
  ]
]

def length l:&:list:_elem -> result:num [
  local-scope
  load-inputs
  result <- copy 0
  {
    break-unless l
    result <- add result, 1
    l <- rest l
    loop
  }
]

# insert 'x' after 'in'
def insert x:_elem, in:&:list:_elem -> in:&:list:_elem [
  local-scope
  load-inputs
  new-node:&:list:_elem <- new {(list _elem): type}
  *new-node <- put *new-node, value:offset, x
  next-node:&:list:_elem <- get *in, next:offset
  *in <- put *in, next:offset, new-node
  *new-node <- put *new-node, next:offset, next-node
]

scenario inserting-into-list [
  local-scope
  list:&:list:num <- push 3, null
  list <- push 4, list
  list <- push 5, list
  run [
    list2:&:list:num <- rest list  # inside list
    list2 <- insert 6, list2
    # check structure
    list2 <- copy list
    10:num/raw <- first list2
    list2 <- rest list2
    11:num/raw <- first list2
    list2 <- rest list2
    12:num/raw <- first list2
    list2 <- rest list2
    13:num/raw <- first list2
  ]
  memory-should-contain [
    10 <- 5  # scanning next
    11 <- 4
    12 <- 6  # inserted element
    13 <- 3
  ]
]

scenario inserting-at-end-of-list [
  local-scope
  list:&:list:num <- push 3, null
  list <- push 4, list
  list <- push 5, list
  run [
    list2:&:list:num <- rest list  # inside list
    list2 <- rest list2  # now at end of list
    list2 <- insert 6, list2
    # check structure like before
    list2 <- copy list
    10:num/raw <- first list2
    list2 <- rest list2
    11:num/raw <- first list2
    list2 <- rest list2
    12:num/raw <- first list2
    list2 <- rest list2
    13:num/raw <- first list2
  ]
  memory-should-contain [
    10 <- 5  # scanning next
    11 <- 4
    12 <- 3
    13 <- 6  # inserted element
  ]
]

scenario inserting-after-start-of-list [
  local-scope
  list:&:list:num <- push 3, null
  list <- push 4, list
  list <- push 5, list
  run [
    list <- insert 6, list
    # check structure like before
    list2:&:list:num <- copy list
    10:num/raw <- first list2
    list2 <- rest list2
    11:num/raw <- first list2
    list2 <- rest list2
    12:num/raw <- first list2
    list2 <- rest list2
    13:num/raw <- first list2
  ]
  memory-should-contain [
    10 <- 5  # scanning next
    11 <- 6  # inserted element
    12 <- 4
    13 <- 3
  ]
]

# remove 'x' from its surrounding list 'in'
#
# Returns null if and only if list is empty. Beware: in that case any other
# pointers to the head are now invalid.
def remove x:&:list:_elem/contained-in:in, in:&:list:_elem -> in:&:list:_elem [
  local-scope
  load-inputs
  # if 'x' is null, return
  return-unless x
  next-node:&:list:_elem <- rest x
  # clear next pointer of 'x'
  *x <- put *x, next:offset, null
  # if 'x' is at the head of 'in', return the new head
  at-head?:bool <- equal x, in
  return-if at-head?, next-node
  # compute prev-node
  prev-node:&:list:_elem <- copy in
  curr:&:list:_elem <- rest prev-node
  {
    return-unless curr
    found?:bool <- equal curr, x
    break-if found?
    prev-node <- copy curr
    curr <- rest curr
  }
  # set its next pointer to skip 'x'
  *prev-node <- put *prev-node, next:offset, next-node
]

scenario removing-from-list [
  local-scope
  list:&:list:num <- push 3, null
  list <- push 4, list
  list <- push 5, list
  run [
    list2:&:list:num <- rest list  # second element
    list <- remove list2, list
    10:bool/raw <- equal list2, null
    # check structure like before
    list2 <- copy list
    11:num/raw <- first list2
    list2 <- rest list2
    12:num/raw <- first list2
    20:&:list:num/raw <- rest list2
  ]
  memory-should-contain [
    10 <- 0  # remove returned non-null
    11 <- 5  # scanning next, skipping deleted element
    12 <- 3
    20 <- 0  # no more elements
  ]
]

scenario removing-from-start-of-list [
  local-scope
  list:&:list:num <- push 3, null
  list <- push 4, list
  list <- push 5, list
  run [
    list <- remove list, list
    # check structure like before
    list2:&:list:num <- copy list
    10:num/raw <- first list2
    list2 <- rest list2
    11:num/raw <- first list2
    20:&:list:num/raw <- rest list2
  ]
  memory-should-contain [
    10 <- 4  # scanning next, skipping deleted element
    11 <- 3
    20 <- 0  # no more elements
  ]
]

scenario removing-from-end-of-list [
  local-scope
  list:&:list:num <- push 3, null
  list <- push 4, list
  list <- push 5, list
  run [
    # delete last element
    list2:&:list:num <- rest list
    list2 <- rest list2
    list <- remove list2, list
    10:bool/raw <- equal list2, null
    # check structure like before
    list2 <- copy list
    11:num/raw <- first list2
    list2 <- rest list2
    12:num/raw <- first list2
    20:&:list:num/raw <- rest list2
  ]
  memory-should-contain [
    10 <- 0  # remove returned non-null
    11 <- 5  # scanning next, skipping deleted element
    12 <- 4
    20 <- 0  # no more elements
  ]
]

scenario removing-from-singleton-list [
  local-scope
  list:&:list:num <- push 3, null
  run [
    list <- remove list, list
    1:num/raw <- deaddress list
  ]
  memory-should-contain [
    1 <- 0  # back to an empty list
  ]
]

# reverse the elements of a list
# (contributed by Caleb Couch)
def reverse list:&:list:_elem temp:&:list:_elem/contained-in:result -> result:&:list:_elem [
  local-scope
  load-inputs
  return-unless list, temp
  object:_elem <- first, list
  list <- rest list
  temp <- push object, temp
  result <- reverse list, temp
]

scenario reverse-list [
  local-scope
  list:&:list:num <- push 1, null
  list <- push 2, list
  list <- push 3, list
  run [
    stash [list:], list
    list <- reverse list
    stash [reversed:], list
  ]
  trace-should-contain [
    app: list: 3 -> 2 -> 1
    app: reversed: 1 -> 2 -> 3
  ]
]

scenario stash-list [
  local-scope
  list:&:list:num <- push 1, null
  list <- push 2, list
  list <- push 3, list
  run [
    stash [list:], list
  ]
  trace-should-contain [
    app: list: 3 -> 2 -> 1
  ]
]

def to-text in:&:list:_elem -> result:text [
  local-scope
  load-inputs
  buf:&:buffer:char <- new-buffer 80
  buf <- to-buffer in, buf
  result <- buffer-to-array buf
]

# variant of 'to-text' which stops printing after a few elements (and so is robust to cycles)
def to-text-line in:&:list:_elem -> result:text [
  local-scope
  load-inputs
  buf:&:buffer:char <- new-buffer 80
  buf <- to-buffer in, buf, 6  # max elements to display
  result <- buffer-to-array buf
]

def to-buffer in:&:list:_elem, buf:&:buffer:char -> buf:&:buffer:char [
  local-scope
  load-inputs
  {
    break-if in
    buf <- append buf, [[]]
    return
  }
  # append in.value to buf
  val:_elem <- get *in, value:offset
  buf <- append buf, val
  # now prepare next
  next:&:list:_elem <- rest in
  nextn:num <- deaddress next
  return-unless next
  buf <- append buf, [ -> ]
  # and recurse
  remaining:num, optional-input-found?:bool <- next-input
  {
    break-if optional-input-found?
    # unlimited recursion
    buf <- to-buffer next, buf
    return
  }
  {
    break-unless remaining
    # limited recursion
    remaining <- subtract remaining, 1
    buf <- to-buffer next, buf, remaining
    return
  }
  # past recursion depth; insert ellipses and stop
  append buf, [...]
]

scenario stash-empty-list [
  local-scope
  x:&:list:num <- copy null
  run [
    stash x
  ]
  trace-should-contain [
    app: []
  ]
]
pre>
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

                                                                              


                                                                              
 
                                                                          



                                                                        

                              
                             
             
                                 
       

                                               






                         
 
                            
 
                                      
                                                                       
                                     
             
                                 
       
                                              
                                                    

                                               


                         
            


           
 
                            
 
                                    
                                   
             
                                 
       



                                                           









                                                                          
                                           





                        
                                         




            
 
                            
 
                                    
                                   
                     
                                   
             
                                 
       

                                               







                         
                                                                                                             
 
                                          
                                   
                     
                                                                       
                                         
             
                                 
       

                                                      
   
                                           





           
                                                                                                                  
 
                
                                                                                       
                                   
          
                          
 

                                                           

                            





                                                                             
                       
                                                                     
                                                                      
                     

                                                                  

                       
                                                                                             
                        





                                                    

                                               

                                                  
                                                    
                                             
                               
 
                                                        

                                                     
                                   
                                







                                                                                                   
                                                            

                                          

 

                                            
                                           

                        
                                                                                              
 



                                                  
                                                                    

                                       
                                    
                                                                                                                                                              

          
                                                 


                                                                                                                                                                                           

        

                                                
                     
                                    






                                                                 
                                                                                      

                                       
                                    
                                                                                                                                                                        





                                                                                                                                                                                                         
                                                 


                                                                                                                                                                                                     

        

                                                
                     
                                    
                                    
                                                                                      


        


                                                                        

                








                                        
       
                                                                     


















                                                                                                                                                        

                                                 
                                                                                                  

                                          
                              
                                                                                                                    
                                                     

             
                                                                                        
                                                                                              
                                      
                                   

                                                                                                 


                                  
                                                                                    
                                                                                            
                                          


                                                                                                                                                                                                                                                                                                
                                                       


               
                          
                                                                                                            
                                     
                                         



                                                                                                                                                                                                                             
                                                                                       
                        
                                                                                                                                                                                                                                      

       

                                                             


                                                                                                                                                                                                                                                                                     
                                                     

             
                              
                                                                                                                 
                                                     

             

                                        
                         
                                                                                            

                   

 




                                                                         
                                                                                                                  



                                                    
                                                                                                                                  






























                                                                        

   



                                             
                                                  



                                       







                                                


















                                                                                                                                                        
                                                                                                  
                
                                                                                        
                                                    

                                                                               

                    
                                       
     
                  

   
//: Clean syntax to manipulate and check the screen in scenarios.
//: Instructions 'assume-screen' and 'screen-should-contain' implicitly create
//: a variable called 'screen' that is accessible to later instructions in the
//: scenario. 'screen-should-contain' can check unicode characters in the fake
//: screen

//: first make sure we don't mangle these instructions in other transforms
:(before "End initialize_transform_rewrite_literal_string_to_text()")
recipes_taking_literal_strings.insert("screen-should-contain");
recipes_taking_literal_strings.insert("screen-should-contain-in-color");

:(scenarios run_mu_scenario)
:(scenario screen_in_scenario)
scenario screen-in-scenario [
  local-scope
  assume-screen 5/width, 3/height
  run [
    a:char <- copy 97/a
    screen:&:screen <- print screen:&:screen, a
  ]
  screen-should-contain [
  #  01234
    .a    .
    .     .
    .     .
  ]
]
# checks are inside scenario

:(scenario screen_in_scenario_unicode)
# screen-should-contain can check unicode characters in the fake screen
scenario screen-in-scenario-unicode [
  local-scope
  assume-screen 5/width, 3/height
  run [
    lambda:char <- copy 955/greek-small-lambda
    screen:&:screen <- print screen:&:screen, lambda
    a:char <- copy 97/a
    screen:&:screen <- print screen:&:screen, a
  ]
  screen-should-contain [
  #  01234
    .λa   .
    .     .
    .     .
  ]
]
# checks are inside scenario

:(scenario screen_in_scenario_color)
scenario screen-in-scenario-color [
  local-scope
  assume-screen 5/width, 3/height
  run [
    lambda:char <- copy 955/greek-small-lambda
    screen:&:screen <- print screen:&:screen, lambda, 1/red
    a:char <- copy 97/a
    screen:&:screen <- print screen:&:screen, a, 7/white
  ]
  # screen-should-contain shows everything
  screen-should-contain [
  #  01234
    .λa   .
    .     .
    .     .
  ]
  # screen-should-contain-in-color filters out everything except the given
  # color, all you see is the 'a' in white.
  screen-should-contain-in-color 7/white, [
  #  01234
    . a   .
    .     .
    .     .
  ]
  # ..and the λ in red.
  screen-should-contain-in-color 1/red, [
  #  01234
    .λ    .
    .     .
    .     .
  ]
]
# checks are inside scenario

:(scenario screen_in_scenario_error)
% Scenario_testing_scenario = true;
% Hide_errors = true;
scenario screen-in-scenario-error [
  local-scope
  assume-screen 5/width, 3/height
  run [
    a:char <- copy 97/a
    screen:&:screen <- print screen:&:screen, a
  ]
  screen-should-contain [
  #  01234
    .b    .
    .     .
    .     .
  ]
]
+error: F - screen-in-scenario-error: expected screen location (0, 0) to contain 98 ('b') instead of 97 ('a')

:(scenario screen_in_scenario_color_error)
% Scenario_testing_scenario = true;
% Hide_errors = true;
# screen-should-contain can check unicode characters in the fake screen
scenario screen-in-scenario-color-error [
  local-scope
  assume-screen 5/width, 3/height
  run [
    a:char <- copy 97/a
    screen:&:screen <- print screen:&:screen, a, 1/red
  ]
  screen-should-contain-in-color 2/green, [
  #  01234
    .a    .
    .     .
    .     .
  ]
]
+error: F - screen-in-scenario-color-error: expected screen location (0, 0) to contain 'a' in color 2 instead of 1

:(scenarios run)
:(scenario convert_names_does_not_fail_when_mixing_special_names_and_numeric_locations)
% Scenario_testing_scenario = true;
def main [
  screen:num <- copy 1:num
]
-error: mixing variable names and numeric addresses in main
$error: 0
:(scenarios run_mu_scenario)

//: It's easier to implement assume-screen and other similar scenario-only
//: primitives if they always write to a fixed location. So we'll assign a
//: single fixed location for the per-scenario screen, keyboard, file system,
//: etc. Carve space for these fixed locations out of the reserved-for-test
//: locations.

:(before "End Globals")
extern const int Max_variables_in_scenarios = Reserved_for_tests-100;
int Next_predefined_global_for_scenarios = Max_variables_in_scenarios;
:(before "End Reset")
assert(Next_predefined_global_for_scenarios < Reserved_for_tests);

:(before "End Globals")
// Scenario Globals.
extern const int SCREEN = next_predefined_global_for_scenarios(/*size_of(address:screen)*/2);
// End Scenario Globals.
:(code)
int next_predefined_global_for_scenarios(int size) {
  int result = Next_predefined_global_for_scenarios;
  Next_predefined_global_for_scenarios += size;
  return result;
}

//: give 'screen' a fixed location in scenarios
:(before "End Special Scenario Variable Names(r)")
Name[r]["screen"] = SCREEN;
//: make 'screen' always a raw location in scenarios
:(before "End is_special_name Special-cases")
if (s == "screen") return true;

:(before "End Rewrite Instruction(curr, recipe result)")
// rewrite 'assume-screen width, height' to
// 'screen:&:screen <- new-fake-screen width, height'
if (curr.name == "assume-screen") {
  curr.name = "new-fake-screen";
  if (!curr.products.empty()) {
    raise << result.name << ": 'assume-screen' has no products\n" << end();
  }
  else if (!starts_with(result.name, "scenario_")) {
    raise << result.name << ": 'assume-screen' can't be called here, only in scenarios\n" << end();
  }
  else {
    assert(curr.products.empty());
    curr.products.push_back(reagent("screen:&:screen/raw"));
    curr.products.at(0).set_value(SCREEN);
  }
}

:(scenario assume_screen_shows_up_in_errors)
% Hide_errors = true;
scenario assume-screen-shows-up-in-errors [
  assume-screen width, 5
]
+error: assume-screen-shows-up-in-errors: missing type for 'width' in 'assume-screen width, 5'

//: screen-should-contain is a regular instruction
:(before "End Primitive Recipe Declarations")
SCREEN_SHOULD_CONTAIN,
:(before "End Primitive Recipe Numbers")
put(Recipe_ordinal, "screen-should-contain", SCREEN_SHOULD_CONTAIN);
:(before "End Primitive Recipe Checks")
case SCREEN_SHOULD_CONTAIN: {
  if (SIZE(inst.ingredients) != 1) {
    raise << maybe(get(Recipe, r).name) << "'screen-should-contain' requires exactly one ingredient, but got '" << to_original_string(inst) << "'\n" << end();
    break;
  }
  if (!is_literal_text(inst.ingredients.at(0))) {
    raise << maybe(get(Recipe, r).name) << "first ingredient of 'screen-should-contain' should be a literal string, but got '" << inst.ingredients.at(0).original_string << "'\n" << end();
    break;
  }
  break;
}
:(before "End Primitive Recipe Implementations")
case SCREEN_SHOULD_CONTAIN: {
  if (!Passed) break;
  assert(scalar(ingredients.at(0)));
  check_screen(current_instruction().ingredients.at(0).name, -1);
  break;
}

:(before "End Primitive Recipe Declarations")
SCREEN_SHOULD_CONTAIN_IN_COLOR,
:(before "End Primitive Recipe Numbers")
put(Recipe_ordinal, "screen-should-contain-in-color", SCREEN_SHOULD_CONTAIN_IN_COLOR);
:(before "End Primitive Recipe Checks")
case SCREEN_SHOULD_CONTAIN_IN_COLOR: {
  if (SIZE(inst.ingredients) != 2) {
    raise << maybe(get(Recipe, r).name) << "'screen-should-contain-in-color' requires exactly two ingredients, but got '" << to_original_string(inst) << "'\n" << end();
    break;
  }
  if (!is_mu_number(inst.ingredients.at(0))) {
    raise << maybe(get(Recipe, r).name) << "first ingredient of 'screen-should-contain-in-color' should be a number (color code), but got '" << inst.ingredients.at(0).original_string << "'\n" << end();
    break;
  }
  if (!is_literal_text(inst.ingredients.at(1))) {
    raise << maybe(get(Recipe, r).name) << "second ingredient of 'screen-should-contain-in-color' should be a literal string, but got '" << inst.ingredients.at(1).original_string << "'\n" << end();
    break;
  }
  break;
}
:(before "End Primitive Recipe Implementations")
case SCREEN_SHOULD_CONTAIN_IN_COLOR: {
  if (!Passed) break;
  assert(scalar(ingredients.at(0)));
  assert(scalar(ingredients.at(1)));
  check_screen(current_instruction().ingredients.at(1).name, ingredients.at(0).at(0));
  break;
}

:(before "End Types")
// scan an array of characters in a unicode-aware, bounds-checked manner
struct raw_string_stream {
  int index;
  const int max;
  const char* buf;

  raw_string_stream(const string&);
  uint32_t get();  // unicode codepoint
  uint32_t peek();  // unicode codepoint
  bool at_end() const;
  void skip_whitespace_and_comments();
};

:(code)
void check_screen(const string& expected_contents, const int color) {
  int screen_location = get_or_insert(Memory, SCREEN+/*skip address alloc id*/1) + /*skip payload alloc id*/1;
  reagent screen("x:screen");  // just to ensure screen.type is reclaimed
  int screen_data_location = find_element_location(screen_location, "data", screen.type, "check_screen");  // type: address:array:character
  assert(screen_data_location >= 0);
//?   cerr << "screen data is at location " << screen_data_location << '\n';
  int screen_data_start = get_or_insert(Memory, screen_data_location+/*skip address alloc id*/1) + /*skip payload alloc id*/1;  // type: array:character
//?   cerr << "screen data start is at " << screen_data_start << '\n';
  int screen_width_location = find_element_location(screen_location, "num-columns", screen.type, "check_screen");
//?   cerr << "screen width is at location " << screen_width_location << '\n';
  int screen_width = get_or_insert(Memory, screen_width_location);
//?   cerr << "screen width: " << screen_width << '\n';
  int screen_height_location = find_element_location(screen_location, "num-rows", screen.type, "check_screen");
//?   cerr << "screen height is at location " << screen_height_location << '\n';
  int screen_height = get_or_insert(Memory, screen_height_location);
//?   cerr << "screen height: " << screen_height << '\n';
  int top_index_location= find_element_location(screen_location, "top-idx", screen.type, "check_screen");
//?   cerr << "top of screen is at location " << top_index_location << '\n';
  int top_index = get_or_insert(Memory, top_index_location);
//?   cerr << "top of screen is index " << top_index << '\n';
  raw_string_stream cursor(expected_contents);
  // todo: too-long expected_contents should fail
  for (int i=0, row=top_index/screen_width;  i < screen_height;  ++i, row=(row+1)%screen_height) {
    cursor.skip_whitespace_and_comments();
    if (cursor.at_end()) break;
    if (cursor.get() != '.') {
      raise << maybe(current_recipe_name()) << "each row of the expected screen should start with a '.'\n" << end();
      if (!Scenario_testing_scenario) Passed = false;
      return;
    }
    int addr = screen_data_start+/*length*/1+row*screen_width* /*size of screen-cell*/2;
    for (int column = 0;  column < screen_width;  ++column, addr+= /*size of screen-cell*/2) {
      const int cell_color_offset = 1;
      uint32_t curr = cursor.get();
      if (get_or_insert(Memory, addr) == 0 && isspace(curr)) continue;
      if (curr == ' ' && color != -1 && color != get_or_insert(Memory, addr+cell_color_offset)) {
        // filter out other colors
        continue;
      }
      if (get_or_insert(Memory, addr) != 0 && get_or_insert(Memory, addr) == curr) {
        if (color == -1 || color == get_or_insert(Memory, addr+cell_color_offset)) continue;
        // contents match but color is off
        if (!Hide_errors) cerr << '\n';
        raise << "F - " << maybe(current_recipe_name()) << "expected screen location (" << row << ", " << column << ") to contain '" << unicode_character_at(addr) << "' in color " << color << " instead of " << no_scientific(get_or_insert(Memory, addr+cell_color_offset)) << "\n" << end();
        if (!Hide_errors) dump_screen();
        if (!Scenario_testing_scenario) Passed = false;
        return;
      }

      // really a mismatch
      // can't print multi-byte unicode characters in errors just yet. not very useful for debugging anyway.
      char expected_pretty[10] = {0};
      if (curr < 256 && !iscntrl(curr)) {
        // " ('<curr>')"
        expected_pretty[0] = ' ', expected_pretty[1] = '(', expected_pretty[2] = '\'', expected_pretty[3] = static_cast<unsigned char>(curr), expected_pretty[4] = '\'', expected_pretty[5] = ')', expected_pretty[6] = '\0';
      }
      char actual_pretty[10] = {0};
      if (get_or_insert(Memory, addr) < 256 && !iscntrl(get_or_insert(Memory, addr))) {
        // " ('<curr>')"
        actual_pretty[0] = ' ', actual_pretty[1] = '(', actual_pretty[2] = '\'', actual_pretty[3] = static_cast<unsigned char>(get_or_insert(Memory, addr)), actual_pretty[4] = '\'', actual_pretty[5] = ')', actual_pretty[6] = '\0';
      }

      ostringstream color_phrase;
      if (color != -1) color_phrase << " in color " << color;
      if (!Hide_errors) cerr << '\n';
      raise << "F - " << maybe(current_recipe_name()) << "expected screen location (" << row << ", " << column << ") to contain " << curr << expected_pretty << color_phrase.str() << " instead of " << no_scientific(get_or_insert(Memory, addr)) << actual_pretty << '\n' << end();
      if (!Hide_errors) dump_screen();
      if (!Scenario_testing_scenario) Passed = false;
      return;
    }
    if (cursor.get() != '.') {
      raise << maybe(current_recipe_name()) << "row " << row << " of the expected screen is too long\n" << end();
      if (!Scenario_testing_scenario) Passed = false;
      return;
    }
  }
  cursor.skip_whitespace_and_comments();
  if (!cursor.at_end()) {
    raise << maybe(current_recipe_name()) << "expected screen has too many rows\n" << end();
    Passed = false;
  }
}

const char* unicode_character_at(int addr) {
  int unicode_code_point = static_cast<int>(get_or_insert(Memory, addr));
  return to_unicode(unicode_code_point);
}

raw_string_stream::raw_string_stream(const string& backing) :index(0), max(SIZE(backing)), buf(backing.c_str()) {}

bool raw_string_stream::at_end() const {
  if (index >= max) return true;
  if (tb_utf8_char_length(buf[index]) > max-index) {
    raise << "unicode string seems corrupted at index "<< index << " character " << static_cast<int>(buf[index]) << '\n' << end();
    return true;
  }
  return false;
}

uint32_t raw_string_stream::get() {
  assert(index < max);  // caller must check bounds before calling 'get'
  uint32_t result = 0;
  int length = tb_utf8_char_to_unicode(&result, &buf[index]);
  assert(length != TB_EOF);
  index += length;
  return result;
}

uint32_t raw_string_stream::peek() {
  assert(index < max);  // caller must check bounds before calling 'get'
  uint32_t result = 0;
  int length = tb_utf8_char_to_unicode(&result, &buf[index]);
  assert(length != TB_EOF);
  return result;
}

void raw_string_stream::skip_whitespace_and_comments() {
  while (!at_end()) {
    if (isspace(peek())) get();
    else if (peek() == '#') {
      // skip comment
      get();
      while (peek() != '\n') get();  // implicitly also handles CRLF
    }
    else break;
  }
}

:(before "End Primitive Recipe Declarations")
_DUMP_SCREEN,
:(before "End Primitive Recipe Numbers")
put(Recipe_ordinal, "$dump-screen", _DUMP_SCREEN);
:(before "End Primitive Recipe Checks")
case _DUMP_SCREEN: {
  break;
}
:(before "End Primitive Recipe Implementations")
case _DUMP_SCREEN: {
  dump_screen();
  break;
}

:(code)
void dump_screen() {
  int screen_location = get_or_insert(Memory, SCREEN+/*skip address alloc id*/1) + /*skip payload alloc id*/1;
  reagent screen("x:screen");  // just to ensure screen.type is reclaimed
  int screen_data_location = find_element_location(screen_location, "data", screen.type, "check_screen");  // type: address:array:character
  assert(screen_data_location >= 0);
//?   cerr << "screen data is at location " << screen_data_location << '\n';
  int screen_data_start = get_or_insert(Memory, screen_data_location+/*skip address alloc id*/1) + /*skip payload alloc id*/1;  // type: array:character
//?   cerr << "screen data start is at " << screen_data_start << '\n';
  int screen_width_location = find_element_location(screen_location, "num-columns", screen.type, "check_screen");
//?   cerr << "screen width is at location " << screen_width_location << '\n';
  int screen_width = get_or_insert(Memory, screen_width_location);
//?   cerr << "screen width: " << screen_width << '\n';
  int screen_height_location = find_element_location(screen_location, "num-rows", screen.type, "check_screen");
//?   cerr << "screen height is at location " << screen_height_location << '\n';
  int screen_height = get_or_insert(Memory, screen_height_location);
//?   cerr << "screen height: " << screen_height << '\n';
  int top_index_location= find_element_location(screen_location, "top-idx", screen.type, "check_screen");
//?   cerr << "top of screen is at location " << top_index_location << '\n';
  int top_index = get_or_insert(Memory, top_index_location);
//?   cerr << "top of screen is index " << top_index << '\n';
  for (int i=0, row=top_index/screen_width;  i < screen_height;  ++i, row=(row+1)%screen_height) {
    cerr << '.';
    int curr = screen_data_start+/*length*/1+row*screen_width* /*size of screen-cell*/2;
    for (int col = 0;  col < screen_width;  ++col) {
      if (get_or_insert(Memory, curr))
        cerr << to_unicode(static_cast<uint32_t>(get_or_insert(Memory, curr)));
      else
        cerr << ' ';
      curr += /*size of screen-cell*/2;
    }
    cerr << ".\n";
  }
}