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<!-- Copyright (C) 2003 Red Hat, Inc.                                -->
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<HTML
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><HEAD
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><TITLE
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>An Introduction to Tcl</TITLE
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><meta name="MSSmartTagsPreventParsing" content="TRUE">
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<META
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NAME="GENERATOR"
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CONTENT="Modular DocBook HTML Stylesheet Version 1.76b+
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"><LINK
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REL="HOME"
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TITLE="The eCos Component Writer's Guide"
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HREF="cdl-guide.html"><LINK
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REL="UP"
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TITLE="The CDL Language"
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HREF="language.html"><LINK
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REL="PREVIOUS"
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TITLE="Option Naming Convention"
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HREF="language.naming.html"><LINK
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TITLE="Values and Expressions"
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HREF="language.values.html"></HEAD
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><BODY
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CLASS="SECT1"
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BGCOLOR="#FFFFFF"
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><TABLE
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SUMMARY="Header navigation table"
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WIDTH="100%"
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CELLPADDING="0"
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CELLSPACING="0"
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><TR
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><TH
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COLSPAN="3"
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ALIGN="center"
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>The <SPAN
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CLASS="APPLICATION"
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>eCos</SPAN
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> Component Writer's Guide</TH
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></TR
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><TR
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><TD
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WIDTH="10%"
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ALIGN="left"
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VALIGN="bottom"
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><A
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HREF="language.naming.html"
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ACCESSKEY="P"
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>Prev</A
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></TD
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><TD
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WIDTH="80%"
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ALIGN="center"
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VALIGN="bottom"
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>Chapter 3. The CDL Language</TD
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><TD
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WIDTH="10%"
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ALIGN="right"
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VALIGN="bottom"
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><A
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HREF="language.values.html"
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ACCESSKEY="N"
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>Next</A
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></TD
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></TR
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></TABLE
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><HR
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ALIGN="LEFT"
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WIDTH="100%"></DIV
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><DIV
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CLASS="SECT1"
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><H1
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CLASS="SECT1"
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><A
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NAME="LANGUAGE.TCL">An Introduction to Tcl</H1
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><P
90
>All <SPAN
91
CLASS="APPLICATION"
92
>CDL</SPAN
93
> scripts are implemented as <SPAN
94
CLASS="APPLICATION"
95
>Tcl</SPAN
96
> scripts, and are read in by
97
running the data through a standard <SPAN
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CLASS="APPLICATION"
99
>Tcl</SPAN
100
> interpreter, extended with a
101
small number of additional commands such as
102
<TT
103
CLASS="LITERAL"
104
>cdl_option</TT
105
> and <TT
106
CLASS="LITERAL"
107
>cdl_component</TT
108
>.
109
Often it is not necessary to know the full details of <SPAN
110
CLASS="APPLICATION"
111
>Tcl</SPAN
112
> syntax.
113
Instead it is possible to copy an existing script, perform some copy
114
and paste operations, and make appropriate changes to names and to
115
various properties. However there are also cases where an
116
understanding of <SPAN
117
CLASS="APPLICATION"
118
>Tcl</SPAN
119
> syntax is very desirable, for example:</P
120
><TABLE
121
BORDER="5"
122
BGCOLOR="#E0E0F0"
123
WIDTH="70%"
124
><TR
125
><TD
126
><PRE
127
CLASS="PROGRAMLISTING"
128
>cdl_option CYGDAT_UITRON_MEMPOOLFIXED_EXTERNS {
129
    display       "Externs for initialization"
130
    flavor        data
131
    default_value {"static char fpool1[ 2000 ], \\\n\
132
                                fpool2[ 2000 ], \\\n\
133
                                fpool3[ 2000 ];"}
134
    &#8230;
135
}</PRE
136
></TD
137
></TR
138
></TABLE
139
><P
140
>This causes the <TT
141
CLASS="LITERAL"
142
>cdl_option</TT
143
> command to be executed, which in turn
144
evaluates its body in a recursive invocation of the <SPAN
145
CLASS="APPLICATION"
146
>Tcl</SPAN
147
> interpreter.
148
When the <SPAN
149
CLASS="PROPERTY"
150
>default_value</SPAN
151
> property is encountered the braces around the
152
value part are processed by the interpreter, stopping it from doing
153
further processing of the braced contents (except for backslash
154
processing at the end of a line, that is special). In particular it
155
prevents command substitution for
156
<TT
157
CLASS="LITERAL"
158
>[&nbsp;2000&nbsp;]</TT
159
>. A single argument will be
160
passed to the <SPAN
161
CLASS="PROPERTY"
162
>default_value</SPAN
163
> command which expects a <SPAN
164
CLASS="APPLICATION"
165
>CDL</SPAN
166
>
167
expression, so the expression parsing code is passed the following:</P
168
><TABLE
169
BORDER="5"
170
BGCOLOR="#E0E0F0"
171
WIDTH="70%"
172
><TR
173
><TD
174
><PRE
175
CLASS="SCREEN"
176
>"static char fpool1[ 2000 ], \\\n fpool2[ 2000 ], \\\n fpool3[ 2000 ];"</PRE
177
></TD
178
></TR
179
></TABLE
180
><P
181
>The <SPAN
182
CLASS="APPLICATION"
183
>CDL</SPAN
184
> expression parsing code will treat this as a simple string
185
constant, as opposed to a more complicated expression involving other
186
options and various operators. The string parsing code will perform
187
the usual backslash substitutions so the actual default value will be:</P
188
><TABLE
189
BORDER="5"
190
BGCOLOR="#E0E0F0"
191
WIDTH="70%"
192
><TR
193
><TD
194
><PRE
195
CLASS="SCREEN"
196
>static char fpool1[ 2000 ], \
197
 fpool2[ 2000 ], \
198
 fpool3[ 2000 ];</PRE
199
></TD
200
></TR
201
></TABLE
202
><P
203
>If the user does not modify the option's value then the following
204
will be generated in the appropriate configuration header file:</P
205
><TABLE
206
BORDER="5"
207
BGCOLOR="#E0E0F0"
208
WIDTH="70%"
209
><TR
210
><TD
211
><PRE
212
CLASS="PROGRAMLISTING"
213
>#define CYGDAT_UITRON_MEMPOOLFIXED_EXTERNS static char fpool1[ 2000 ], \
214
 fpool2[ 2000 ], \
215
 fpool3[ 2000 ];</PRE
216
></TD
217
></TR
218
></TABLE
219
><P
220
>Getting this desired result usually requires an understanding of both
221
<SPAN
222
CLASS="APPLICATION"
223
>Tcl</SPAN
224
> syntax and <SPAN
225
CLASS="APPLICATION"
226
>CDL</SPAN
227
> expression syntax. Sometimes it is possible to
228
substitute a certain amount of trial and error instead, but this may
229
prove frustrating. It is also worth pointing out that many <SPAN
230
CLASS="APPLICATION"
231
>CDL</SPAN
232
>
233
scripts do not involve this level of complexity. On the other hand,
234
some of the more advanced features of the <SPAN
235
CLASS="APPLICATION"
236
>CDL</SPAN
237
> language involve
238
fragments of <SPAN
239
CLASS="APPLICATION"
240
>Tcl</SPAN
241
> code, for example the <SPAN
242
CLASS="PROPERTY"
243
>define_proc</SPAN
244
> property. To
245
use these component writers will need to know about the full <SPAN
246
CLASS="APPLICATION"
247
>Tcl</SPAN
248
>
249
language as well as the syntax.</P
250
><P
251
>Although the current example may seem to suggest that <SPAN
252
CLASS="APPLICATION"
253
>Tcl</SPAN
254
> is rather
255
complicated, it is actually a very simple yet powerful scripting
256
language: the syntax is defined by just eleven rules. On occasion this
257
simplicity means that Tcl's behavior is subtly different from other
258
languages, which can confuse newcomers.</P
259
><P
260
>When the Tcl interpreter is passed some data such as
261
<TT
262
CLASS="LITERAL"
263
>puts&nbsp;Hello</TT
264
>, it splits this data into a command
265
and its arguments. The command will be terminated by a newline or by a
266
semicolon, unless one of the quoting mechanisms is used. The command
267
and each of its arguments are separated by white space. So in the
268
following example:</P
269
><TABLE
270
BORDER="5"
271
BGCOLOR="#E0E0F0"
272
WIDTH="70%"
273
><TR
274
><TD
275
><PRE
276
CLASS="SCREEN"
277
>puts Hello
278
set x 42</PRE
279
></TD
280
></TR
281
></TABLE
282
><P
283
>This will result in two separate commands being executed. The first
284
command is <TT
285
CLASS="LITERAL"
286
>puts</TT
287
> and is passed a single argument,
288
<TT
289
CLASS="LITERAL"
290
>Hello</TT
291
>. The second command is <TT
292
CLASS="LITERAL"
293
>set</TT
294
>
295
and is passed two arguments, <TT
296
CLASS="LITERAL"
297
>x</TT
298
> and
299
<TT
300
CLASS="LITERAL"
301
>42</TT
302
>. The intervening newline character serves to
303
terminate the first command, and a semi-colon separator could be used
304
instead: </P
305
><TABLE
306
BORDER="5"
307
BGCOLOR="#E0E0F0"
308
WIDTH="70%"
309
><TR
310
><TD
311
><PRE
312
CLASS="SCREEN"
313
>puts Hello;set x 42</PRE
314
></TD
315
></TR
316
></TABLE
317
><P
318
>Any white space surrounding the semicolon is just ignored because it
319
does not serve to separate arguments.</P
320
><P
321
>Now consider the following:</P
322
><TABLE
323
BORDER="5"
324
BGCOLOR="#E0E0F0"
325
WIDTH="70%"
326
><TR
327
><TD
328
><PRE
329
CLASS="SCREEN"
330
>set x Hello world</PRE
331
></TD
332
></TR
333
></TABLE
334
><P
335
>This is not valid <SPAN
336
CLASS="APPLICATION"
337
>Tcl</SPAN
338
>. It is an attempt to invoke the
339
<TT
340
CLASS="LITERAL"
341
>set</TT
342
> command with three arguments:
343
<TT
344
CLASS="LITERAL"
345
>x</TT
346
>, <TT
347
CLASS="LITERAL"
348
>Hello</TT
349
>, and
350
<TT
351
CLASS="LITERAL"
352
>world</TT
353
>. The <TT
354
CLASS="LITERAL"
355
>set</TT
356
> only takes two
357
arguments, a variable name and a value, so it is necessary to combine
358
the data into a single argument by quoting:</P
359
><TABLE
360
BORDER="5"
361
BGCOLOR="#E0E0F0"
362
WIDTH="70%"
363
><TR
364
><TD
365
><PRE
366
CLASS="SCREEN"
367
>set x "Hello world"</PRE
368
></TD
369
></TR
370
></TABLE
371
><P
372
>When the <SPAN
373
CLASS="APPLICATION"
374
>Tcl</SPAN
375
> interpreter encounters the first quote character it
376
treats all subsequent data up to but not including the closing quote
377
as part of the current argument. The quote marks are removed by the
378
interpreter, so the second argument passed to the
379
<TT
380
CLASS="LITERAL"
381
>set</TT
382
> command is just <TT
383
CLASS="LITERAL"
384
>Hello world</TT
385
>
386
without the quote characters. This can be significant in the context
387
of <SPAN
388
CLASS="APPLICATION"
389
>CDL</SPAN
390
> scripts. For example:</P
391
><TABLE
392
BORDER="5"
393
BGCOLOR="#E0E0F0"
394
WIDTH="70%"
395
><TR
396
><TD
397
><PRE
398
CLASS="PROGRAMLISTING"
399
>cdl_option CYG_HAL_STARTUP {
400
    &#8230;
401
    default_value "RAM"
402
}</PRE
403
></TD
404
></TR
405
></TABLE
406
><P
407
>The <SPAN
408
CLASS="APPLICATION"
409
>Tcl</SPAN
410
> interpreter strips off the quote marks so the <SPAN
411
CLASS="APPLICATION"
412
>CDL</SPAN
413
>
414
expression parsing code sees <TT
415
CLASS="LITERAL"
416
>RAM</TT
417
> instead of
418
<TT
419
CLASS="LITERAL"
420
>"RAM"</TT
421
>. It will treat this as a reference to
422
some unknown option <TT
423
CLASS="VARNAME"
424
>RAM</TT
425
> rather than as a string
426
constant, and the expression evaluation code will use a value of
427
<TT
428
CLASS="LITERAL"
429
>0</TT
430
> when it encounters an option that is not
431
currently loaded. Therefore the option
432
<TT
433
CLASS="VARNAME"
434
>CYG_HAL_STARTUP</TT
435
> ends up with a default value of
436
<TT
437
CLASS="LITERAL"
438
>0</TT
439
>. Either braces or backslashes should be used to
440
avoid this, for example
441
<TT
442
CLASS="LITERAL"
443
>default_value&nbsp;{&nbsp;"RAM"&nbsp;}</TT
444
>. </P
445
><DIV
446
CLASS="NOTE"
447
><BLOCKQUOTE
448
CLASS="NOTE"
449
><P
450
><B
451
>Note: </B
452
>There are long-term plans to implement some sort of <SPAN
453
CLASS="APPLICATION"
454
>CDL</SPAN
455
> validation
456
utility <SPAN
457
CLASS="APPLICATION"
458
>cdllint</SPAN
459
> which
460
could catch common errors like this one.</P
461
></BLOCKQUOTE
462
></DIV
463
><P
464
>A quoted argument continues until the closing quote character is
465
encountered, which means that it can span multiple lines. Newline or
466
semicolon characters do not terminate the current command in such
467
cases. <SPAN
468
CLASS="PROPERTY"
469
>description</SPAN
470
> properties usually make use of this:</P
471
><TABLE
472
BORDER="5"
473
BGCOLOR="#E0E0F0"
474
WIDTH="70%"
475
><TR
476
><TD
477
><PRE
478
CLASS="PROGRAMLISTING"
479
>cdl_package CYGPKG_ERROR {
480
    description   "
481
        This package contains the common list of error and
482
        status codes. It is held centrally to allow
483
        packages to interchange error codes and status
484
        codes in a common way, rather than each package
485
        having its own conventions for error/status
486
        reporting. The error codes are modelled on the
487
        POSIX style naming e.g. EINVAL etc. This package
488
        also provides the standard strerror() function to
489
        convert error codes to textual representation."
490
    &#8230;
491
}</PRE
492
></TD
493
></TR
494
></TABLE
495
><P
496
>The <SPAN
497
CLASS="APPLICATION"
498
>Tcl</SPAN
499
> interpreter supports much the same forms of backslash
500
substitution as other common programming languages. Some backslash
501
sequences such as <TT
502
CLASS="LITERAL"
503
>\n</TT
504
> will be replaced by the
505
appropriate character. The sequence <TT
506
CLASS="LITERAL"
507
>\\</TT
508
> will be
509
replaced by a single backslash. A backslash at the very end of a line
510
will cause that backslash, the newline character, and any white space
511
at the start of the next line to be replaced by a single space. Hence
512
the following two Tcl commands are equivalent:</P
513
><TABLE
514
BORDER="5"
515
BGCOLOR="#E0E0F0"
516
WIDTH="70%"
517
><TR
518
><TD
519
><PRE
520
CLASS="PROGRAMLISTING"
521
>puts  "Hello\nworld\n"
522
puts \
523
"Hello
524
world
525
"</PRE
526
></TD
527
></TR
528
></TABLE
529
><P
530
>If a <SPAN
531
CLASS="PROPERTY"
532
>description</SPAN
533
> string needs to contain quote marks or other
534
special characters then backslash escapes can be used. In addition to
535
quote and backslash characters, the Tcl interpreter treats square
536
brackets, the <TT
537
CLASS="LITERAL"
538
>$</TT
539
> character, and braces specially.
540
Square brackets are used for command substitution, for example:</P
541
><TABLE
542
BORDER="5"
543
BGCOLOR="#E0E0F0"
544
WIDTH="70%"
545
><TR
546
><TD
547
><PRE
548
CLASS="SCREEN"
549
>puts "The answer is [expr 6 * 9]"</PRE
550
></TD
551
></TR
552
></TABLE
553
><P
554
>When the Tcl interpreter encounters the square brackets it will treat
555
the contents as another command that should be executed first, and the
556
result of executing that is used when continuing to process the
557
script. In this case the Tcl interpreter will execute the command
558
<TT
559
CLASS="LITERAL"
560
>expr 6 * 9</TT
561
>, yielding a result of 42
562
<A
563
NAME="AEN1270"
564
HREF="#FTN.AEN1270"
565
>[1]</A
566
>
567
and then the
568
Tcl interpreter will execute <TT
569
CLASS="LITERAL"
570
>puts "The answer is 42"</TT
571
>.
572
It should be noted that the interpreter performs only one level
573
of substitution: if the result of performing command substitution
574
performs further special characters such as square brackets then these
575
will not be treated specially.</P
576
><P
577
>Command substitution will not prove useful for many <SPAN
578
CLASS="APPLICATION"
579
>CDL</SPAN
580
> scripts,
581
except for e.g. a <SPAN
582
CLASS="PROPERTY"
583
>define_proc</SPAN
584
> property which involves a fragment of
585
<SPAN
586
CLASS="APPLICATION"
587
>Tcl</SPAN
588
> code. Potentially there are some interesting uses, for example
589
to internationalize <SPAN
590
CLASS="PROPERTY"
591
>display</SPAN
592
> strings. However care does have to be
593
taken to avoid unexpected command substitution, for example if an
594
option description involves square brackets then typically these would
595
require backslash-escapes.</P
596
><P
597
>The <TT
598
CLASS="LITERAL"
599
>$</TT
600
> character is used in Tcl scripts to perform
601
variable substitution:</P
602
><TABLE
603
BORDER="5"
604
BGCOLOR="#E0E0F0"
605
WIDTH="70%"
606
><TR
607
><TD
608
><PRE
609
CLASS="PROGRAMLISTING"
610
>set x [expr 6 * 9]
611
puts "The answer is $x"</PRE
612
></TD
613
></TR
614
></TABLE
615
><P
616
>Variable substitution, like command substitution, is unlikely to
617
prove useful for many <SPAN
618
CLASS="APPLICATION"
619
>CDL</SPAN
620
> scripts except in the context of
621
<SPAN
622
CLASS="APPLICATION"
623
>Tcl</SPAN
624
> fragments. If it is necessary to have a <TT
625
CLASS="LITERAL"
626
>$</TT
627
>
628
character then a backslash escape may have to be used.</P
629
><P
630
>Braces are used to collect a sequence of characters into a single
631
argument, just like quotes. The difference is that variable, command
632
and backslash substitution do not occur inside braces (with the
633
sole exception of backslash substitution at the end of a line).
634
Therefore given a line in a <SPAN
635
CLASS="APPLICATION"
636
>CDL</SPAN
637
> script such as:</P
638
><TABLE
639
BORDER="5"
640
BGCOLOR="#E0E0F0"
641
WIDTH="70%"
642
><TR
643
><TD
644
><PRE
645
CLASS="PROGRAMLISTING"
646
>default_value {"RAM"}</PRE
647
></TD
648
></TR
649
></TABLE
650
><P
651
>The braces are stripped off by the <SPAN
652
CLASS="APPLICATION"
653
>Tcl</SPAN
654
> interpreter, leaving
655
<TT
656
CLASS="LITERAL"
657
>"RAM"</TT
658
> which will be handled as a string constant by
659
the expression parsing code. The same effect could be achieved using
660
one of the following:</P
661
><TABLE
662
BORDER="5"
663
BGCOLOR="#E0E0F0"
664
WIDTH="70%"
665
><TR
666
><TD
667
><PRE
668
CLASS="PROGRAMLISTING"
669
>default_value \"RAM\"
670
default_value "\"RAM\""</PRE
671
></TD
672
></TR
673
></TABLE
674
><P
675
>Generally the use of braces is less confusing. At this stage it is
676
worth noting that the basic format of <SPAN
677
CLASS="APPLICATION"
678
>CDL</SPAN
679
> data makes use of
680
braces:</P
681
><TABLE
682
BORDER="5"
683
BGCOLOR="#E0E0F0"
684
WIDTH="70%"
685
><TR
686
><TD
687
><PRE
688
CLASS="PROGRAMLISTING"
689
>cdl_option &lt;name&gt; {
690
     &#8230;
691
};</PRE
692
></TD
693
></TR
694
></TABLE
695
><P
696
>The <TT
697
CLASS="LITERAL"
698
>cdl_option</TT
699
> command is passed two arguments, a name and a body,
700
where the body consists of everything inside the braces but not the
701
braces themselves. This body can then be executed in a recursive
702
invocation of the <SPAN
703
CLASS="APPLICATION"
704
>Tcl</SPAN
705
> interpreter. If a <SPAN
706
CLASS="APPLICATION"
707
>CDL</SPAN
708
> script contains
709
mismatched braces then the interpreter is likely to get rather
710
confused and the resulting diagnostics may be difficult to understand. </P
711
><P
712
>Comments in Tcl scripts are introduced by a hash character
713
<TT
714
CLASS="LITERAL"
715
>#</TT
716
>. However, a hash character only introduces a
717
comment if it occurs where a command is expected. Consider the
718
following:</P
719
><TABLE
720
BORDER="5"
721
BGCOLOR="#E0E0F0"
722
WIDTH="70%"
723
><TR
724
><TD
725
><PRE
726
CLASS="PROGRAMLISTING"
727
># This is a comment
728
puts "Hello" # world</PRE
729
></TD
730
></TR
731
></TABLE
732
><P
733
>The first line is a valid comment, since the hash character occurs
734
right at the start where a command name is expected. The second line
735
does not contain a comment. Instead it is an attempt to invoke the
736
<TT
737
CLASS="LITERAL"
738
>puts</TT
739
> command with three arguments:
740
<TT
741
CLASS="LITERAL"
742
>Hello</TT
743
>, <TT
744
CLASS="LITERAL"
745
>#</TT
746
> and
747
<TT
748
CLASS="LITERAL"
749
>world</TT
750
>. These are not valid arguments for the
751
<TT
752
CLASS="LITERAL"
753
>puts</TT
754
> command so an error will be raised.
755
If the second line was rewritten as:</P
756
><TABLE
757
BORDER="5"
758
BGCOLOR="#E0E0F0"
759
WIDTH="70%"
760
><TR
761
><TD
762
><PRE
763
CLASS="PROGRAMLISTING"
764
>puts "Hello"; # world</PRE
765
></TD
766
></TR
767
></TABLE
768
><P
769
>then this is a valid Tcl script. The semicolon identifies the end of
770
the current command, so the hash character occurs at a point where the
771
next command would start and hence it is interpreted as the start of a
772
comment.</P
773
><P
774
>This handling of comments can lead to subtle behavior. Consider the
775
following:</P
776
><TABLE
777
BORDER="5"
778
BGCOLOR="#E0E0F0"
779
WIDTH="70%"
780
><TR
781
><TD
782
><PRE
783
CLASS="PROGRAMLISTING"
784
>cdl_option WHATEVER {
785
# This is a comment }
786
    default_value 0
787
    &#8230;
788
}</PRE
789
></TD
790
></TR
791
></TABLE
792
><P
793
>Consider the way the Tcl interpreter processes this. The command name
794
and the first argument do not pose any special difficulties. The
795
opening brace is interpreted as the start of the next argument, which
796
continues until a closing brace is encountered. In this case the
797
closing brace occurs on the second line, so the second argument passed
798
to <TT
799
CLASS="LITERAL"
800
>cdl_option</TT
801
> is
802
<TT
803
CLASS="LITERAL"
804
>\n&nbsp;&nbsp;&nbsp;&nbsp;#&nbsp;This&nbsp;is&nbsp;a&nbsp;comment</TT
805
>. This second argument is processed in a recursive
806
invocation of the Tcl interpreter and does not contain any commands,
807
just a comment. Top-level script processing then resumes, and the next
808
command that is encountered is <TT
809
CLASS="LITERAL"
810
>default_value</TT
811
>. Since
812
the parser is not currently processing a configuration option this is
813
an error. Later on the Tcl interpreter would encounter a closing brace
814
by itself, which is also an error.</P
815
><P
816
>For component writers who need more information about <SPAN
817
CLASS="APPLICATION"
818
>Tcl</SPAN
819
>,
820
especially about the language rather than the syntax, various
821
resources are available. A reasonable starting point is the
822
<A
823
HREF="http://www.tcl.tk/scripting/"
824
TARGET="_top"
825
>Scriptics developer
826
web site</A
827
>.</P
828
></DIV
829
><H3
830
CLASS="FOOTNOTES"
831
>Notes</H3
832
><TABLE
833
BORDER="0"
834
CLASS="FOOTNOTES"
835
WIDTH="100%"
836
><TR
837
><TD
838
ALIGN="LEFT"
839
VALIGN="TOP"
840
WIDTH="5%"
841
><A
842
NAME="FTN.AEN1270"
843
HREF="language.tcl.html#AEN1270"
844
>[1]</A
845
></TD
846
><TD
847
ALIGN="LEFT"
848
VALIGN="TOP"
849
WIDTH="95%"
850
><P
851
>It is possible that some versions of the Tcl interpreter will instead
852
produce a result of 54 when asked to multiply six by nine. Appropriate
853
<A
854
HREF="http://www.douglasadams.com/creations/hhgg.html"
855
TARGET="_top"
856
>reference
857
documentation</A
858
> should be consulted for more information on why
859
42 is in fact the correct answer.</P
860
></TD
861
></TR
862
></TABLE
863
><DIV
864
CLASS="NAVFOOTER"
865
><HR
866
ALIGN="LEFT"
867
WIDTH="100%"><TABLE
868
SUMMARY="Footer navigation table"
869
WIDTH="100%"
870
BORDER="0"
871
CELLPADDING="0"
872
CELLSPACING="0"
873
><TR
874
><TD
875
WIDTH="33%"
876
ALIGN="left"
877
VALIGN="top"
878
><A
879
HREF="language.naming.html"
880
ACCESSKEY="P"
881
>Prev</A
882
></TD
883
><TD
884
WIDTH="34%"
885
ALIGN="center"
886
VALIGN="top"
887
><A
888
HREF="cdl-guide.html"
889
ACCESSKEY="H"
890
>Home</A
891
></TD
892
><TD
893
WIDTH="33%"
894
ALIGN="right"
895
VALIGN="top"
896
><A
897
HREF="language.values.html"
898
ACCESSKEY="N"
899
>Next</A
900
></TD
901
></TR
902
><TR
903
><TD
904
WIDTH="33%"
905
ALIGN="left"
906
VALIGN="top"
907
>Option Naming Convention</TD
908
><TD
909
WIDTH="34%"
910
ALIGN="center"
911
VALIGN="top"
912
><A
913
HREF="language.html"
914
ACCESSKEY="U"
915
>Up</A
916
></TD
917
><TD
918
WIDTH="33%"
919
ALIGN="right"
920
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921
>Values and Expressions</TD
922
></TR
923
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924
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925
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926
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927
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