summaryrefslogtreecommitdiff
path: root/macros/plain/contrib/literate/makeprog.web
blob: ea477fe0f5384d36636eed46b6720807a1b77619 (plain)
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
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
@                                                           % sect.    2
The program begins with a fairly normal header, made up of
pieces that will mostly be filled in later.  The input comes
from files |doc_file| and |change_file|, the output goes to
file |prog_file|.  Messages from \MAKEPROG{} are written to
|term_out|, which is supposed to be the terminal.
@^system dependencies@>

If it is necessary to abort the job because of a fatal
error, the program calls the `|jump_out|' procedure, which
goes to the label |end_of_MAKEPROG|.

@d end_of_MAKEPROG = 9999 {go here to wrap it up}

@p @t\4@>@<Compiler directives@>@/
program MAKEPROG(@!doc_file,@!change_file,@!prog_file);
label end_of_MAKEPROG; {go here to finish}
const @<Constants in the outer block@>@;
type @<Types in the outer block@>@;
var @<Globals in the outer block@>@;
@t\4@>@<Error handling procedures@>@;
procedure initialize;
  var @<Local variables for initialization@>@;
  begin @<Set initial values@>
  end;


@                                                           % sect.    3
Some of this code is optional for use when debugging only;
such material is enclosed between the delimiters \&{debug}
and \&{gubed}.

@d debug==@{ {change this to `$\\{debug}\equiv\null$' when debugging}
@d gubed==@t@>@} {change this to `$\\{gubed}\equiv\null$' when debugging}
@f debug==repeat
@f gubed==until


@                                                           % sect.    4
The \PASCAL\ compiler used to develop this system has
``compiler directives'' that can appear in comments whose
first character is a dollar sign.  In production versions of
\MAKEPROG{} these directives tell the compiler that it is
safe to avoid range checks and to leave out the extra code
it inserts for the \PASCAL\ debugger's benefit.
@^system dependencies@>

@<Compiler directives@>=
@{@&@=$D-@> @} {no debug overhead}
@!debug @{@&@=$D+@> @}@+ gubed @; {but turn everything on when debugging}


@                                                           % sect.    5
Labels are given symbolic names by the following
definitions.  We insert the label `|exit|' just before the
`\&{end}' of a procedure in which we have used the
`|return|' statement defined below; the label `|restart|' is
occasionally used at the very beginning of a procedure; and
the label `|reswitch|' is occasionally used just prior to a
\&{case} statement in which some cases change the conditions
and we wish to branch to the newly applicable case.  Loops
that are set up with the \&{loop} construction defined below
are commonly exited by going to `|done|' or to `|found|' or
to `|not_found|', and they are sometimes repeated by going
to `|continue|'.

@d exit=10 {go here to leave a procedure}
@d restart=20 {go here to start a procedure again}
@d reswitch=21 {go here to start a case statement again}
@d continue=22 {go here to resume a loop}
@d done=30 {go here to exit a loop}
@d found=31 {go here when you've found it}
@d not_found=32 {go here when you've found something else}


@                                                           % sect.    6
Here are some macros for common programming idioms.

@d incr(#) == #:=#+1 {increase a variable by unity}
@d decr(#) == #:=#-1 {decrease a variable by unity}
@d loop == @+ while true do@+ {repeat over and over until a |goto| happens}
@d do_nothing == {empty statement}
@d return == goto exit {terminate a procedure call}
@f return == nil
@f loop == xclause


@                                                           % sect.    7
We assume that |case| statements may include a default case
that applies if no matching label is found.  Thus, we shall
use constructions like
@^system dependencies@>
$$
\vbox{\halign{#\hfil\cr
|case x of|\cr
   \quad 1: $\langle\,$code for $x=1\,\rangle$;\cr
   \quad 3: $\langle\,$code for $x=3\,\rangle$;\cr
   \quad |othercases| $\langle\,$code for |x<>1| and |x<>3|$\,\rangle$\cr
|endcases|\cr
}}
$$
since most \PASCAL\ compilers have plugged this hole in the
language by incorporating some sort of default mechanism.
For example, the compiler used to develop \.{WEB} and \TeX\
allows `|others|:' as a default label, and other \PASCAL s
allow syntaxes like `\&{else}' or `\&{otherwise}' or
`\\{otherwise}:', etc.  The definitions of |othercases| and
|endcases| should be changed to agree with local
conventions.  (Of course, if no default mechanism is
available, the |case| statements of this program must be
extended by listing all remaining cases.)

@d othercases == others: {default for cases not listed explicitly}
@d endcases == @+end {follows the default case in an extended |case| statement}
@f othercases == else
@f endcases == end


@                                                           % sect.    8
The following parameter is set big enough to be sufficient
for most applications of \MAKEPROG{}.

@<Constants...@>=
@!buf_size=500; {maximum length of input line}


@                                                           % sect.    9
A global variable called |history| will contain one of four values
at the end of every run: |spotless| means that no unusual messages were
printed; |harmless_message| means that a message of possible interest
was printed but no serious errors were detected; |error_message| means that
at least one error was found; |fatal_message| means that the program
terminated abnormally. The value of |history| does not influence the
behavior of the program; it is simply computed for the convenience
of systems that might want to use such information.

@d spotless=0 {|history| value for normal jobs}
@d harmless_message=1 {|history| value when non-serious info was printed}
@d error_message=2 {|history| value when an error was noted}
@d fatal_message=3 {|history| value when we had to stop prematurely}
@#
@d mark_harmless==@t@>@+if history=spotless then history:=harmless_message
@d mark_error==history:=error_message
@d mark_fatal==history:=fatal_message

@<Glob...@>=@!history:spotless..fatal_message; {how bad was this run?}

@                                                           % sect.   10
@<Set init...@>=history:=spotless;





@* The character set.                                       % sect.   11

\noindent One of the main goals in the design of \MAKEPROG{}
has been to make it readily portable between a wide variety
of computers.  Yet \MAKEPROG{} by its very nature must use a
greater variety of characters than most computer programs
deal with, and character encoding is one of the areas in
which existing machines differ most widely from each other.

To resolve this problem, all input to \MAKEPROG{} is
converted to an internal seven-bit code that is essentially
standard \ASCII{}, the ``American Standard Code for
Information Interchange.'' The conversion is done
immediately when each character is read in.  Conversely,
characters are converted from \ASCII{} to the user's
external representation just before they are output.  Such
an internal code is never relevant to users of \MAKEPROG{}.

\noindent Here is a table of the standard visible \ASCII{} codes:
$$\def\:{\char\count255\global\advance\count255 by 1}
\count255='40
\vbox{
\hbox{\hbox to 40pt{\it\hfill0\/\hfill}%
\hbox to 40pt{\it\hfill1\/\hfill}%
\hbox to 40pt{\it\hfill2\/\hfill}%
\hbox to 40pt{\it\hfill3\/\hfill}%
\hbox to 40pt{\it\hfill4\/\hfill}%
\hbox to 40pt{\it\hfill5\/\hfill}%
\hbox to 40pt{\it\hfill6\/\hfill}%
\hbox to 40pt{\it\hfill7\/\hfill}}
\vskip 4pt
\hrule
\def\^{\vrule height 10.5pt depth 4.5pt}
\halign{\hbox to 0pt{\hskip -24pt\O{#0}\hfill}&\^
\hbox to 40pt{\tt\hfill#\hfill\^}&
&\hbox to 40pt{\tt\hfill#\hfill\^}\cr
04&\:&\:&\:&\:&\:&\:&\:&\:\cr\noalign{\hrule}
05&\:&\:&\:&\:&\:&\:&\:&\:\cr\noalign{\hrule}
06&\:&\:&\:&\:&\:&\:&\:&\:\cr\noalign{\hrule}
07&\:&\:&\:&\:&\:&\:&\:&\:\cr\noalign{\hrule}
10&\:&\:&\:&\:&\:&\:&\:&\:\cr\noalign{\hrule}
11&\:&\:&\:&\:&\:&\:&\:&\:\cr\noalign{\hrule}
12&\:&\:&\:&\:&\:&\:&\:&\:\cr\noalign{\hrule}
13&\:&\:&\:&\:&\:&\:&\:&\:\cr\noalign{\hrule}
14&\:&\:&\:&\:&\:&\:&\:&\:\cr\noalign{\hrule}
15&\:&\:&\:&\:&\:&\:&\:&\:\cr\noalign{\hrule}
16&\:&\:&\:&\:&\:&\:&\:&\:\cr\noalign{\hrule}
17&\:&\:&\:&\:&\:&\:&\:\cr}
\hrule width 280pt}$$
(Actually, of course, code @"20 is an invisible blank
space.) Code @"3E was once an upward arrow (\.{\char'13}),
and code @"3F was once a left arrow (\.^^X), in olden times
when the first draft of \ASCII{} code was prepared; but
\MAKEPROG{} works with today's standard \ASCII{} in which
those codes represent circumflex and underline as shown.

@<Types...@>=
@!ASCII_code=0..@"7F; {seven-bit numbers, a subrange of the integers}


@                                                           % sect.   12
The original \PASCAL\ compiler was designed in the late 60s,
when six-bit character sets were common, so it did not make
provision for lowercase letters.  Nowadays, of course, we
need to deal with both capital and small letters in a
convenient way, so \MAKEPROG{} assumes that it is being used
with a \PASCAL\ whose character set contains at least the
characters of standard \ASCII{} as listed above.  Some
\PASCAL\ compilers use the original name |char| for the data
type associated with the characters in text files, while
other \PASCAL s consider |char| to be a 64-element subrange
of a larger data type that has some other name.

In order to accommodate this difference, we shall use the
name |text_char| to stand for the data type of the
characters in the input and output files.  We shall also
assume that |text_char| consists of the elements
|chr(first_text_char)| through |chr(last_text_char)|,
inclusive.  The following definitions should be adjusted if
necessary.
@^system dependencies@>

@d text_char == char {the data type of characters in text files}
@d first_text_char=0 {ordinal number of the smallest element of |text_char|}
@d last_text_char=127 {ordinal number of the largest element of |text_char|}

@<Types...@>=
@!text_file=packed file of text_char;


@                                                           % sect.   13
The \MAKEPROG{} processor convert between \ASCII{} code and
the user's external character set by means of arrays |xord|
and |xchr| that are analogous to \PASCAL's |ord| and |chr|
functions.

@<Globals...@>=
@!xord: array [text_char] of ASCII_code;
  {specifies conversion of input characters}
@!xchr: array [ASCII_code] of text_char;
  {specifies conversion of output characters}


@                                                           % sect.   14
If we assume that every system using \.{WEB} is able to read
and write the visible characters of standard \ASCII{}
(although not necessarily using the \ASCII{} codes to
represent them), the following assignment statements
initialize most of the |xchr| array properly, without
needing any system-dependent changes.  For example, the
statement \.{xchr["A"]:=\'A\'} that appears in the present
\.{WEB} file might be encoded in, say, \hbox{\mc EBCDIC}
code on the external medium on which it resides, but
\.{TANGLE} will convert from this external code to \ASCII{}
and back again.  Therefore the assignment statement
\.{XCHR[65]:=\'A\'} will appear in the corresponding
\PASCAL\ file, and \PASCAL\ will compile this statement so
that |xchr[65]| receives the character \.A in the external
(|char|) code.  Note that it would be quite incorrect to say
\.{xchr["A"]:="A"}, because |"A"| is a constant of type
|integer|, not |char|, and because we have $|"A"|=65$
regardless of the external character set.

@<Set init...@>=
xchr[" "]:=' ';
xchr["!"]:='!';
xchr[""""]:='"';
xchr["#"]:='#';
xchr["$"]:='$';
xchr["%"]:='%';
xchr["&"]:='&';
xchr["'"]:='''';@/
xchr["("]:='(';
xchr[")"]:=')';
xchr["*"]:='*';
xchr["+"]:='+';
xchr[","]:=',';
xchr["-"]:='-';
xchr["."]:='.';
xchr["/"]:='/';@/
xchr["0"]:='0';
xchr["1"]:='1';
xchr["2"]:='2';
xchr["3"]:='3';
xchr["4"]:='4';
xchr["5"]:='5';
xchr["6"]:='6';
xchr["7"]:='7';@/
xchr["8"]:='8';
xchr["9"]:='9';
xchr[":"]:=':';
xchr[";"]:=';';
xchr["<"]:='<';
xchr["="]:='=';
xchr[">"]:='>';
xchr["?"]:='?';@/
xchr["@@"]:='@@';
xchr["A"]:='A';
xchr["B"]:='B';
xchr["C"]:='C';
xchr["D"]:='D';
xchr["E"]:='E';
xchr["F"]:='F';
xchr["G"]:='G';@/
xchr["H"]:='H';
xchr["I"]:='I';
xchr["J"]:='J';
xchr["K"]:='K';
xchr["L"]:='L';
xchr["M"]:='M';
xchr["N"]:='N';
xchr["O"]:='O';@/
xchr["P"]:='P';
xchr["Q"]:='Q';
xchr["R"]:='R';
xchr["S"]:='S';
xchr["T"]:='T';
xchr["U"]:='U';
xchr["V"]:='V';
xchr["W"]:='W';@/
xchr["X"]:='X';
xchr["Y"]:='Y';
xchr["Z"]:='Z';
xchr["["]:='[';
xchr["\"]:='\';
xchr["]"]:=']';
xchr["^"]:='^';
xchr["_"]:='_';@/
xchr["`"]:='`';
xchr["a"]:='a';
xchr["b"]:='b';
xchr["c"]:='c';
xchr["d"]:='d';
xchr["e"]:='e';
xchr["f"]:='f';
xchr["g"]:='g';@/
xchr["h"]:='h';
xchr["i"]:='i';
xchr["j"]:='j';
xchr["k"]:='k';
xchr["l"]:='l';
xchr["m"]:='m';
xchr["n"]:='n';
xchr["o"]:='o';@/
xchr["p"]:='p';
xchr["q"]:='q';
xchr["r"]:='r';
xchr["s"]:='s';
xchr["t"]:='t';
xchr["u"]:='u';
xchr["v"]:='v';
xchr["w"]:='w';@/
xchr["x"]:='x';
xchr["y"]:='y';
xchr["z"]:='z';
xchr["{"]:='{';
xchr["|"]:='|';
xchr["}"]:='}';
xchr["~"]:='~';@/
xchr[0]:=' '; xchr[@"7F]:=' '; {these \ASCII{} codes are not used}


@                                                           % sect.   15
Some of the nonprintable \ASCII{} codes have been given
symbolic names in \MAKEPROG{} because they are used with a
special meaning.

@d tab_mark=@"09              {\ASCII{} code used as tab-skip}
@d line_feed=@"0A             {\ASCII{} code thrown away at end of line}
@d form_feed=@"0C             {\ASCII{} code used at end of page}
@d carriage_return=@"0D       {\ASCII{} code used at end of line}


@                                                           % sect.   16
When we initialize the |xord| array and the remaining parts of |xchr|,
it will be convenient to make use of an index variable, |i|.

@<Local variables for init...@>=
@!i:0..last_text_char;


@                                                           % sect.   17
Here now is the system-dependent part of the character set.
If \MAKEPROG{} is being implemented on a garden-variety
\PASCAL\ for which only standard \ASCII{} codes will appear
in the input and output files, you don't need to make any
changes here.
@^system dependencies@>

Changes to the present module will make \MAKEPROG{} more
friendly on computers that have an extended character set,
so that one can type things like Umlaute.  If you have an
extended set of characters that are easily incorporated into
text files, you can assign codes arbitrarily here, giving an
|xchr| equivalent to whatever characters the users of
\MAKEPROG{} are allowed to have in their input files,
provided that unsuitable characters do not correspond to
special codes like |carriage_return| that are listed above.

@<Set init...@>=
for i:=1 to " "-1 do xchr[i]:=' ';


@                                                           % sect.   18
The following system-independent code makes the |xord| array
contain a suitable inverse to the information in |xchr|.

@<Set init...@>=
for i:=first_text_char to last_text_char do xord[chr(i)]:=" ";
for i:=1 to "~" do xord[xchr[i]]:=i;





@* Basic Input and output.

\noindent The input conventions of \MAKEPROG{} are identical
to those of \.{WEB}.  Therefore people who need to make
modifications to both systems should be able to do so
without too many headaches.


@                                                           % sect.   20
Terminal output is done by writing on file |term_out|, which
is assumed to consist of characters of type |text_char|:
@^system dependencies@>

@d print(#)==write(term_out,#) {`|print|' means write on the terminal}
@d print_ln(#)==write_ln(term_out,#) {`|print|' and then start new line}
@d new_line==write_ln(term_out) {start new line}
@d print_nl(#)==  {print information starting on a new line}
  begin new_line; print(#);
  end

@<Globals...@>=
@!term_out:text_file; {the terminal as an output file}


@                                                           % sect.   21
Different systems have different ways of specifying that the
output on a certain file will appear on the user's terminal.
Here is one way to do this on the \PASCAL{} system that was
used in \.{TANGLE}'s initial development.
@^system dependencies@>

@<Set init...@>=
rewrite(term_out,'TTY:'); {send |term_out| output to the terminal}


@                                                           % sect.   22
The |update_terminal| procedure is called when we want to
make sure that everything we have output to the terminal so
far has actually left the computer's internal buffers and
been sent.
@^system dependencies@>

@d update_terminal == break(term_out) {empty the terminal output buffer}


@                                                           % sect.   23
The main input comes from |doc_file|; this input may be
overridden by changes in |change_file|.  (If |change_file|
is empty, there are no changes.)

@<Globals...@>=
@!doc_file:text_file; {primary input}
@!change_file:text_file; {updates}


@                                                           % sect.   24
The following code opens the input files.  Since these files
were listed in the program header, we assume that the
\PASCAL\ runtime system has already checked that suitable
file names have been given; therefore no additional error
checking needs to be done.
@^system dependencies@>

@< Set init... @>=
reset(doc_file); reset(change_file);


@                                                           % sect.   25
The output goes to |prog_file|.

@<Globals...@>=
@!prog_file: text_file;


@                                                           % sect.   26
The following code opens |prog_file|.  Since this file is
listed in the program header, we assume that the \PASCAL\
runtime system has checked that a suitable external file
name have been given.
@^system dependencies@>

@<Set init...@>=
rewrite(prog_file);


@                                                           % sect.   27
Input goes into an array called |buffer|.

@<Globals...@>=
@!buffer: array[0..buf_size] of ASCII_code;


@                                                           % sect.   28
The |input_ln| procedure brings the next line of input from
the specified file into the |buffer| array and returns the
value |true|, unless the file has already been entirely
read, in which case it returns |false|.  The conventions of
\.{WEB} are followed; i.e., |ASCII_code| numbers
representing the next line of the file are input into
|buffer[0]|, |buffer[1]|, \dots, |buffer[limit-1]|; trailing
blanks are ignored; and the global variable |limit| is set
to the length of the line.  The value of |limit| must be
strictly less than |buf_size|.
@^system dependencies@>

We assume that none of the |ASCII_code| values of
|buffer[j]| for |0<=j<limit| is equal to 0, @"7F,
|line_feed|, |form_feed|, or |carriage_return|.

@p
function input_ln(var f:text_file):boolean; {inputs a line or returns |false|}
   var final_limit:0..buf_size; {|limit| without trailing blanks}
   begin limit:=0; final_limit:=0;
   if eof(f) then input_ln:=false
   else  begin
      while not eoln(f) do
         begin buffer[limit]:=xord[f^]; get(f);
         incr(limit);
         if (buffer[limit-1]<>" ") and (buffer[limit-1]<>tab_mark) then
            final_limit:=limit;
         if limit=buf_size then
            begin while not eoln(f) do get(f);
            decr(limit); {keep |buffer[buf_size]| empty}
            print_nl('! Input line too long'); error; mark_error;
@.Input line too long@>
            end;
         end;
      read_ln(f); limit:=final_limit; input_ln:=true;
      end;
   end;





@* Reporting errors to the user.                            % sect.   29

\noindent Errors are reported to the user by saying
$$
   \hbox{`|err_print('! Error message')|'},
$$
followed by `|jump_out|' if no recovery from the error is
provided.  This will print the error message followed by an
indication of where the error was spotted in the source
file.  Note that no period follows the error message, since
the error routine will automatically supply a period.

\noindent The actual error indications are provided by a
procedure called |error|.

@d err_print(#)==begin print_nl(#); error; mark_error; end

@<Error handling...@>=
procedure error; {prints '\..' and location of error message}
   begin @< Print error location @>;
   update_terminal;
   end;


@                                                           % sect.   32
The error locations can be indicated by using the global
variables |line| and |changing|, which tell respectively the
the current line number and whether or not the current line
is from |change_file| or |doc_file|.  This routine should be
modified on systems whose standard text editor has special
line-numbering conventions.
@^system dependencies@>

@< Print error location @>=
begin
if changing then  print('. (change file ') @+ else print('. (');
print_ln('l.', line:1, ')');
print(' '); {this space separates the message from future output}
end


@                                                           % sect.   34
The |jump_out| procedure just cuts across all active
procedure levels and jumps out of the program.  This is the
only non-local |goto| statement in \MAKEPROG{}.  It is used
when no recovery from a particular error has been provided.

Some \PASCAL\ compilers do not implement non-local |goto| statements.
@^system dependencies@>
In such cases the code that appears at label
|end_of_MAKEPROG| should be copied into the |jump_out|
procedure, followed by a call to a system procedure that
terminates the program.

@d fatal_error(#)==begin print_nl(#); error; mark_fatal; jump_out;
  end

@<Error handling...@>=
procedure jump_out;
begin goto end_of_MAKEPROG;
end;


@                                                           % sect.   35
Sometimes the program's behavior is far different from what
it should be, and \MAKEPROG{} prints an error message that
is really for the \MAKEPROG{} maintenance person, not the
user.  In such cases the program says
|confusion('indication of where we are')|.

@d confusion(#)==fatal_error('! This can''t happen (',#,')')
@.This can't happen@>





@* The kernel.

\noindent Let us now consider the routine |get_line| that
takes care of merging |change_file| into |doc_file|.  The
|get_line| procedure also updates the line numbers for error
messages.

@<Globals...@>=
@!line:integer; {the number of the current line in the current file}
@!other_line:integer; {the number of the current line in the input file that
  is not currently being read}
@!temp_line:integer; {used when interchanging |line| with |other_line|}
@!limit:0..buf_size; {the last character position occupied in the buffer}
@!input_has_ended: boolean; {if |true|, there is no more input}
@!changing: boolean; {if |true|, the current line is from |change_file|}


@                                                           % sect.  128
As we change |changing| from |true| to |false| and back
again, we must remember to swap the values of |line| and
|other_line| so that the |err_print| routine will be sure to
report the correct line number.

@d change_changing==
         begin changing := not changing;@/
         temp_line:=other_line; other_line:=line; line:=temp_line;
         end {$|line| \BA |other_line|$}


@                                                           % sect.  129
When |changing| is |false|, the next line of |change_file|
is kept in |change_buffer[0..change_limit-1]|, for purposes
of comparison with the next line of |doc_file|.  After the
change file has been completely input, we set
|change_limit:=0|, so that no further matches will be made.

@<Globals...@>=
@!change_buffer:array[0..buf_size] of ASCII_code;
@!change_limit:0..buf_size; {the last position occupied in |change_buffer|}


@                                                           % sect.  130
Here's a simple function that checks if the two buffers are
different.

@p function lines_dont_match:boolean;
label exit;
var k:0..buf_size; {index into the buffers}
begin lines_dont_match:=true;
if change_limit<>limit then return;
if limit>0 then
  for k:=0 to limit-1 do if change_buffer[k]<>buffer[k] then return;
lines_dont_match:=false;
exit: end;


@                                                           % sect.  131
Procedure |prime_the_change_buffer| sets |change_buffer| in
preparation for the next matching operation.  Since blank
lines in the change file are not used for matching, we have
|(change_limit=0)and not changing| if and only if the change
file is exhausted.  This procedure is called only when
|changing| is true; hence error messages will be reported
correctly.

@p procedure prime_the_change_buffer;
label continue, done, exit;
var k:0..buf_size; {index into the buffers}
begin change_limit:=0; {this value will be used if the change file ends}
@<Skip over comment lines in the change file; |return| if end of file@>;
@<Skip to the next nonblank line; |return| if end of file@>;
@<Move |buffer| and |limit| to |change_buffer| and |change_limit|@>;
exit: end;


@                                                           % sect.  132
While looking for a line that begins with \.{@@x} in the
change file, we allow lines that begin with \.{@@}, as long
as they don't begin with \.{@@y} or \.{@@z} (which would
probably indicate that the change file is fouled up).

@<Skip over comment lines in the change file...@>=
loop@+  begin incr(line);
  if not input_ln(change_file) then return;
  if limit<2 then goto continue;
  if buffer[0]<>"@@" then goto continue;
  if (buffer[1]>="X")and(buffer[1]<="Z") then
    buffer[1]:=buffer[1]+"z"-"Z"; {lowercasify}
  if buffer[1]="x" then goto done;
  if (buffer[1]="y")or(buffer[1]="z") then
    err_print('! Where is the matching @@x?');
@.Where is the match...@>
continue: end;
done:


@                                                           % sect.  133
Here we are looking at lines following the \.{@@x}.

@<Skip to the next nonblank line...@>=
repeat incr(line);
  if not input_ln(change_file) then
    begin err_print('! Change file ended after @@x');
@.Change file ended...@>
    return;
    end;
until limit>0;


@                                                           % sect.  134
@<Move |buffer| and |limit| to |change_buffer| and |change_limit|@>=
begin change_limit:=limit;
for k:=0 to limit-1 do change_buffer[k]:=buffer[k];
end


@                                                           % sect.  135
The following procedure is used to see if the next change
entry should go into effect; it is called only when
|changing| is false.  The idea is to test whether or not the
current contents of |buffer| matches the current contents of
|change_buffer|.  If not, there's nothing more to do; but if
so, a change is called for:  All of the text down to the
\.{@@y} is supposed to match.  An error message is issued if
any discrepancy is found.  Then the procedure prepares to
read the next line from |change_file|.

@p
procedure check_change; {switches to |change_file| if the buffers match}
label exit;
var n:integer; {the number of discrepancies found}
@!k:0..buf_size; {index into the buffers}
begin if lines_dont_match then return;
n:=0;
loop@+  begin change_changing; {now it's |true|}
  incr(line);
  if not input_ln(change_file) then
    begin err_print('! Change file ended before @@y');@/
@.Change file ended...@>
    change_limit:=0;  change_changing; {|false| again}
    return;
    end;
  @<If the current line starts with \.{@@y},
    report any discrepancies and |return|@>;
  @<Move |buffer| and |limit|...@>;
  change_changing; {now it's |false|}
  incr(line);
  if not input_ln(doc_file) then
    begin err_print('! CWEB file ended during a change');
@.CWEB file ended...@>
    input_has_ended:=true; return;
    end;
  if lines_dont_match then incr(n);
  end;
exit: end;


@                                                           % sect.  136
@<If the current line starts with \.{@@y}...@>=
if limit>1 then if buffer[0]="@@" then
  begin if (buffer[1]>="X")and(buffer[1]<="Z") then
    buffer[1]:=buffer[1]+"z"-"Z"; {lowercasify}
  if (buffer[1]="x")or(buffer[1]="z") then
    err_print('! Where is the matching @@y?')
@.Where is the match...@>
  else if buffer[1]="y" then
    begin if n>0 then
      err_print('! Hmm... ',n:1,' of the preceding lines failed to match');
@.Hmm... n of the preceding...@>
    return;
    end;
  end


@                                                           % sect.  137
@< Initialize the input system @>=
begin line:=0; other_line:=0;@/
changing:=true; prime_the_change_buffer; change_changing;@/
limit:=0; buffer[0]:=" "; input_has_ended:=false;
end


@                                                           % sect.  138
The |get_line| procedure puts the next line of merged input
into the buffer and updates the other variables
appropriately.  A space is placed at the right end of the
line.  We output points to show the user the progress in
reading.

@p
procedure get_line; {inputs the next line}
   label restart;
   begin
restart: if changing then
      @<Read from |change_file| and maybe turn off |changing|@>;
   if not changing then
      begin @<Read from |doc_file| and maybe turn on |changing|@>;
      if changing then  goto restart;
      end;
   buffer[limit]:=" ";
   if (line mod 500) = 0 then
      begin print(line:1);  update_terminal;
      end
   else if (line mod 100) = 0 then
         begin print('.');  update_terminal;
         end
      @!debug else begin print('.');  update_terminal; @+ end @+ gubed @;
      ;@/
   end;


@                                                           % sect.  139
@<Read from |doc_file|...@>=
begin incr(line);
if not input_ln(doc_file) then input_has_ended:=true
else if change_limit>0 then check_change;
end


@                                                           % sect.  140
@<Read from |change_file|...@>=
begin incr(line);
if not input_ln(change_file) then
  begin err_print('! Change file ended without @@z');
@.Change file ended...@>
  buffer[0]:="@@"; buffer[1]:="z"; limit:=2;
  end;
if limit>1 then {check if the change has ended}
  if buffer[0]="@@" then
    begin if (buffer[1]>="X")and(buffer[1]<="Z") then
      buffer[1]:=buffer[1]+"z"-"Z"; {lowercasify}
    if (buffer[1]="x")or(buffer[1]="y") then
      err_print('! Where is the matching @@z?')
@.Where is the match...@>
    else if buffer[1]="z" then
      begin prime_the_change_buffer; change_changing;
      end;
    end;
end


@                                                           % sect.  141
At the end of the program, we will tell the user if the
change file had a line that didn't match any relevant line
in |doc_file|.

@<Check that all changes have been read@>=
begin
if change_limit<>0 then {|changing| is false}
   begin
   for limit:=0 to change_limit do  buffer[limit] := change_buffer[limit];
   limit := change_limit;  changing := true;  line := other_line;
   err_print('! Change file entry did not match');
@.Change file entry did not match@>
   end;
end


@
The |put_line| procedure outputs the next line from
|buffer| to |prog_file|. Perhaps we should give here a
progress report, too (with asterisks?)

@p
procedure put_line;
   var i: 0..buf_size;
   begin
   for i:=0 to limit-1 do  write(prog_file, xchr[buffer[i]]);
   write_ln(prog_file);
   end;





@* The main program.                                        % sect.  190

\noindent We have defined some procedures, and it is time to
use them---here is where \MAKEPROG{} starts, and where it
ends.
@^system dependencies@>

@p
   begin initialize;
   print_ln(banner); {print a ``banner line''}
   print_ln(copy_right); print_ln(rights_res); {print a copyright notice}
   @< Initialize the input system @>;
   debug  print_ln('begin copy');
   gubed @;
   @< Copy all program parts to the output @>;
   debug  print_ln('end copy');
   gubed @;
   @< Check that all changes... @>;
end_of_MAKEPROG:
   @#
   {here files should be closed if the operating system requires it}
   @;@#
   @<Print the job |history|@>;
   end.


@
A program part begins after a line that begins with
\.{\\beginprog} and ends before the next line with
\.{\\endprog} starting it. If we find the starting line we
set |state| to |begin_prog|, between to lines |state| has
the value |inner_prog| and with the ending line |state| is
set to |out_of_prog|.

@d begin_prog = 0
@d inner_prog = 1
@d out_of_prog = 2

@< Glob... @>=
@!state: begin_prog..out_of_prog;

@
@< Set init... @>=
state := out_of_prog;


@
After we have read the introducing line for a program part
which is signaled with |state=begin_prog| we change the
state to |inner_prog| to start copy the next line;

@< Copy all program... @>=
begin get_line;
while not input_has_ended do
   begin @< Look at the input line and store in |state| the result @>;
   if state = inner_prog then  put_line
   else if state = begin_prog then  state := inner_prog;
   get_line;
   end;
if state = inner_prog then  err_print('! Input has ended prematurely');
@.Input has ended...@>
end


@
We first define a few macros to improve the readability of
the program part behind. After \.{\\beginprog} no letters
may appear and after \.{\\endprog} either the line is ended
or white space is to be there. The comparison is facilitated
by the fact that |buffer[limit]=" "|, i.e.\ the last
character of a line is always a space.

@d cmp_prog(#) == (buffer[#]="p") and (buffer[#+1]="r") and
                  (buffer[#+2]="o") and (buffer[#+3]="g")
@d cmp_begin == (buffer[1]="b") and (buffer[2]="e") and (buffer[3]="g") and@|
                (buffer[4]="i") and (buffer[5]="n") and cmp_prog(6) and@|
                ((buffer[10]<"A") or (buffer[10]>"Z")) and@|
                ((buffer[10]<"a") or (buffer[10]>"z"))
@d cmp_end == (buffer[1]="e") and (buffer[2]="n") and (buffer[3]="d") and
              cmp_prog(4) and @|
              ((buffer[8]=" ") or (buffer[8]=tab_mark))

@< Look at the input... @>=
begin
if buffer[0] = "\" then
   if limit >= 10 then
      begin @+ if cmp_begin then  state := begin_prog;  @+ end
   else if limit >= 8 then
      if cmp_end then  state := out_of_prog;
end


@                                                           % sect.  195
Some implementations may wish to pass the |history| value to the
operating system so that it can be used to govern whether or not other
programs are started. Here we simply report the history to the user.
@^system dependencies@>

@<Print the job |history|@>=
case history of
spotless: print_nl('(No errors were found.)');
harmless_message: print_nl('(Did you see the warning message above?)');
error_message: print_nl('(Pardon me, but I think I spotted something wrong.)');
fatal_message: print_nl('(That was a fatal error, my friend.)');
end {there are no other cases}





@* System-dependent changes.                                % sect.  196

\noindent This module should be replaced, if necessary, by
changes to the program that are necessary to make
\MAKEPROG{} work at a particular installation.  It is
usually best to design your change file so that all changes
to previous modules preserve the module numbering; then
everybody's version will be consistent with the printed
program.  More extensive changes, which introduce new
modules, can be inserted here; then only the index itself
will get a new module number.
@^system dependencies@>





@* Index.                                                   % sect.  197

\noindent Here is a cross-reference table for the
\MAKEPROG{} processor.  All modules in which an identifier
is used are listed with that identifier, except that
reserved words are indexed only when they appear in format
definitions, and the appearances of identifiers in module
names are not indexed.  Underlined entries correspond to
where the identifier was declared.  Error messages and a few
other things like ``system dependencies'' are indexed here
too.