1pt::pe(n) Parser Tools pt::pe(n)
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6
8 pt::pe - Parsing Expression Serialization
9
11 package require Tcl 8.5
12 package require pt::pe ?1.0.1?
14 package require char
16 ::pt::pe verify serial ?canonvar?
18 ::pt::pe verify-as-canonical serial
20 ::pt::pe canonicalize serial
22 ::pt::pe print serial
24 ::pt::pe bottomup cmdprefix pe
26 cmdprefix pe op arguments
28 ::pt::pe topdown cmdprefix pe
30 ::pt::pe equal seriala serialb
32 ::pt::pe epsilon
34 ::pt::pe dot
36 ::pt::pe alnum
38 ::pt::pe alpha
40 ::pt::pe ascii
42 ::pt::pe control
44 ::pt::pe digit
46 ::pt::pe graph
48 ::pt::pe lower
50 ::pt::pe print
52 ::pt::pe punct
54 ::pt::pe space
56 ::pt::pe upper
58 ::pt::pe wordchar
60 ::pt::pe xdigit
62 ::pt::pe ddigit
64 ::pt::pe terminal t
66 ::pt::pe range ta tb
68 ::pt::pe nonterminal nt
70 ::pt::pe choice pe...
72 ::pt::pe sequence pe...
74 ::pt::pe repeat0 pe
76 ::pt::pe repeat1 pe
78 ::pt::pe optional pe
80 ::pt::pe ahead pe
82 ::pt::pe notahead pe
84______________________________________________________________________________
86
88 Are you lost ? Do you have trouble understanding this document ? In
89 that case please read the overview provided by the Introduction to
90 Parser Tools. This document is the entrypoint to the whole system the
91 current package is a part of.
92 This package provides commands to work with the serializations of pars‐
94 ing expressions as managed by the Parser Tools, and specified in sec‐
95 tion PE serialization format.
96 This is a supporting package in the Core Layer of Parser Tools.
98 IMAGE: arch_core_support
100
102 ::pt::pe verify serial ?canonvar?
103 This command verifies that the content of serial is a valid se‐
104 rialization of a parsing expression and will throw an error if
105 that is not the case. The result of the command is the empty
106 string.
107 If the argument canonvar is specified it is interpreted as the
109 name of a variable in the calling context. This variable will be
110 written to if and only if serial is a valid regular serializa‐
111 tion. Its value will be a boolean, with True indicating that the
112 serialization is not only valid, but also canonical. False will
113 be written for a valid, but non-canonical serialization.
114 For the specification of serializations see the section PE seri‐
116 alization format.
117 ::pt::pe verify-as-canonical serial
119 This command verifies that the content of serial is a valid
120 canonical serialization of a parsing expression and will throw
121 an error if that is not the case. The result of the command is
122 the empty string.
123 For the specification of canonical serializations see the sec‐
125 tion PE serialization format.
126 ::pt::pe canonicalize serial
128 This command assumes that the content of serial is a valid regu‐
129 lar serialization of a parsing expression and will throw an er‐
130 ror if that is not the case.
131 It will then convert the input into the canonical serialization
133 of this parsing expression and return it as its result. If the
134 input is already canonical it will be returned unchanged.
135 For the specification of regular and canonical serializations
137 see the section PE serialization format.
138 ::pt::pe print serial
140 This command assumes that the argument serial contains a valid
141 serialization of a parsing expression and returns a string con‐
142 taining that PE in a human readable form.
143 The exact format of this form is not specified and cannot be re‐
145 lied on for parsing or other machine-based activities.
146 For the specification of serializations see the section PE seri‐
148 alization format.
149 ::pt::pe bottomup cmdprefix pe
151 This command walks the parsing expression pe from the bottom up
152 to the root, invoking the command prefix cmdprefix for each par‐
153 tial expression. This implies that the children of a parsing ex‐
154 pression PE are handled before PE.
155 The command prefix has the signature
157 cmdprefix pe op arguments
159 I.e. it is invoked with the parsing expression pe the
160 walk is currently at, the op'erator in the pe, and the
161 operator's arguments.
162 The result returned by the command prefix replaces pe in
164 the parsing expression it was a child of, allowing trans‐
165 formations of the expression tree.
166 This also means that for all inner parsing expressions
168 the contents of arguments are the results of the command
169 prefix invoked for the children of this inner parsing ex‐
170 pression.
171 ::pt::pe topdown cmdprefix pe
173 This command walks the parsing expression pe from the root down
174 to the leaves, invoking the command prefix cmdprefix for each
175 partial expression. This implies that the children of a parsing
176 expression PE are handled after PE.
177 The command prefix has the same signature as for bottomup, see
179 above.
180 The result returned by the command prefix is ignored.
182 ::pt::pe equal seriala serialb
184 This command tests the two parsing expressions seriala and seri‐
185 alb for structural equality. The result of the command is a
186 boolean value. It will be set to true if the expressions are
187 identical, and false otherwise.
188 String equality is usable only if we can assume that the two
190 parsing expressions are pure Tcl lists.
191 ::pt::pe epsilon
193 This command constructs the atomic parsing expression for ep‐
194 silon.
195 ::pt::pe dot
197 This command constructs the atomic parsing expression for dot.
198 ::pt::pe alnum
200 This command constructs the atomic parsing expression for alnum.
201 ::pt::pe alpha
203 This command constructs the atomic parsing expression for alpha.
204 ::pt::pe ascii
206 This command constructs the atomic parsing expression for ascii.
207 ::pt::pe control
209 This command constructs the atomic parsing expression for con‐
210 trol.
211 ::pt::pe digit
213 This command constructs the atomic parsing expression for digit.
214 ::pt::pe graph
216 This command constructs the atomic parsing expression for graph.
217 ::pt::pe lower
219 This command constructs the atomic parsing expression for lower.
220 ::pt::pe print
222 This command constructs the atomic parsing expression for print.
223 ::pt::pe punct
225 This command constructs the atomic parsing expression for punct.
226 ::pt::pe space
228 This command constructs the atomic parsing expression for space.
229 ::pt::pe upper
231 This command constructs the atomic parsing expression for upper.
232 ::pt::pe wordchar
234 This command constructs the atomic parsing expression for word‐
235 char.
236 ::pt::pe xdigit
238 This command constructs the atomic parsing expression for
239 xdigit.
240 ::pt::pe ddigit
242 This command constructs the atomic parsing expression for
243 ddigit.
244 ::pt::pe terminal t
246 This command constructs the atomic parsing expression for the
247 terminal symbol t.
248 ::pt::pe range ta tb
250 This command constructs the atomic parsing expression for the
251 range of terminal symbols ta ... tb.
252 ::pt::pe nonterminal nt
254 This command constructs the atomic parsing expression for the
255 nonterminal symbol nt.
256 ::pt::pe choice pe...
258 This command constructs the parsing expression representing the
259 ordered or prioritized choice between the argument parsing ex‐
260 pressions. The first argument has the highest priority.
261 ::pt::pe sequence pe...
263 This command constructs the parsing expression representing the
264 sequence of the argument parsing expression. The first argument
265 is the first element of the sequence.
266 ::pt::pe repeat0 pe
268 This command constructs the parsing expression representing the
269 zero or more repetition of the argument parsing expression pe,
270 also known as the kleene closure.
271 ::pt::pe repeat1 pe
273 This command constructs the parsing expression representing the
274 one or more repetition of the argument parsing expression pe,
275 also known as the positive kleene closure.
276 ::pt::pe optional pe
278 This command constructs the parsing expression representing the
279 optionality of the argument parsing expression pe.
280 ::pt::pe ahead pe
282 This command constructs the parsing expression representing the
283 positive lookahead of the argument parsing expression pe.
284 ::pt::pe notahead pe
286 This command constructs the parsing expression representing the
287 negative lookahead of the argument parsing expression pe.
288
290 Here we specify the format used by the Parser Tools to serialize Pars‐
291 ing Expressions as immutable values for transport, comparison, etc.
292 We distinguish between regular and canonical serializations. While a
294 parsing expression may have more than one regular serialization only
295 exactly one of them will be canonical.
296 Regular serialization
298 Atomic Parsing Expressions
300 [1] The string epsilon is an atomic parsing expres‐
302 sion. It matches the empty string.
303 [2] The string dot is an atomic parsing expression. It
305 matches any character.
306 [3] The string alnum is an atomic parsing expression.
308 It matches any Unicode alphabet or digit charac‐
309 ter. This is a custom extension of PEs based on
310 Tcl's builtin command string is.
311 [4] The string alpha is an atomic parsing expression.
313 It matches any Unicode alphabet character. This is
314 a custom extension of PEs based on Tcl's builtin
315 command string is.
316 [5] The string ascii is an atomic parsing expression.
318 It matches any Unicode character below U0080. This
319 is a custom extension of PEs based on Tcl's
320 builtin command string is.
321 [6] The string control is an atomic parsing expres‐
323 sion. It matches any Unicode control character.
324 This is a custom extension of PEs based on Tcl's
325 builtin command string is.
326 [7] The string digit is an atomic parsing expression.
328 It matches any Unicode digit character. Note that
329 this includes characters outside of the [0..9]
330 range. This is a custom extension of PEs based on
331 Tcl's builtin command string is.
332 [8] The string graph is an atomic parsing expression.
334 It matches any Unicode printing character, except
335 for space. This is a custom extension of PEs based
336 on Tcl's builtin command string is.
337 [9] The string lower is an atomic parsing expression.
339 It matches any Unicode lower-case alphabet charac‐
340 ter. This is a custom extension of PEs based on
341 Tcl's builtin command string is.
342 [10] The string print is an atomic parsing expression.
344 It matches any Unicode printing character, includ‐
345 ing space. This is a custom extension of PEs based
346 on Tcl's builtin command string is.
347 [11] The string punct is an atomic parsing expression.
349 It matches any Unicode punctuation character. This
350 is a custom extension of PEs based on Tcl's
351 builtin command string is.
352 [12] The string space is an atomic parsing expression.
354 It matches any Unicode space character. This is a
355 custom extension of PEs based on Tcl's builtin
356 command string is.
357 [13] The string upper is an atomic parsing expression.
359 It matches any Unicode upper-case alphabet charac‐
360 ter. This is a custom extension of PEs based on
361 Tcl's builtin command string is.
362 [14] The string wordchar is an atomic parsing expres‐
364 sion. It matches any Unicode word character. This
365 is any alphanumeric character (see alnum), and any
366 connector punctuation characters (e.g. under‐
367 score). This is a custom extension of PEs based on
368 Tcl's builtin command string is.
369 [15] The string xdigit is an atomic parsing expression.
371 It matches any hexadecimal digit character. This
372 is a custom extension of PEs based on Tcl's
373 builtin command string is.
374 [16] The string ddigit is an atomic parsing expression.
376 It matches any decimal digit character. This is a
377 custom extension of PEs based on Tcl's builtin
378 command regexp.
379 [17] The expression [list t x] is an atomic parsing ex‐
381 pression. It matches the terminal string x.
382 [18] The expression [list n A] is an atomic parsing ex‐
384 pression. It matches the nonterminal A.
385 Combined Parsing Expressions
387 [1] For parsing expressions e1, e2, ... the result of
389 [list / e1 e2 ... ] is a parsing expression as
390 well. This is the ordered choice, aka prioritized
391 choice.
392 [2] For parsing expressions e1, e2, ... the result of
394 [list x e1 e2 ... ] is a parsing expression as
395 well. This is the sequence.
396 [3] For a parsing expression e the result of [list *
398 e] is a parsing expression as well. This is the
399 kleene closure, describing zero or more repeti‐
400 tions.
401 [4] For a parsing expression e the result of [list +
403 e] is a parsing expression as well. This is the
404 positive kleene closure, describing one or more
405 repetitions.
406 [5] For a parsing expression e the result of [list &
408 e] is a parsing expression as well. This is the
409 and lookahead predicate.
410 [6] For a parsing expression e the result of [list !
412 e] is a parsing expression as well. This is the
413 not lookahead predicate.
414 [7] For a parsing expression e the result of [list ?
416 e] is a parsing expression as well. This is the
417 optional input.
418 Canonical serialization
420 The canonical serialization of a parsing expression has the for‐
421 mat as specified in the previous item, and then additionally
422 satisfies the constraints below, which make it unique among all
423 the possible serializations of this parsing expression.
424 [1] The string representation of the value is the canonical
426 representation of a pure Tcl list. I.e. it does not con‐
427 tain superfluous whitespace.
428 [2] Terminals are not encoded as ranges (where start and end
430 of the range are identical).
431 EXAMPLE
433 Assuming the parsing expression shown on the right-hand side of the
434 rule
435 Expression <- Term (AddOp Term)*
437 then its canonical serialization (except for whitespace) is
440 {x {n Term} {* {x {n AddOp} {n Term}}}}
442
445 This document, and the package it describes, will undoubtedly contain
446 bugs and other problems. Please report such in the category pt of the
447 Tcllib Trackers [http://core.tcl.tk/tcllib/reportlist]. Please also
448 report any ideas for enhancements you may have for either package
449 and/or documentation.
450 When proposing code changes, please provide unified diffs, i.e the out‐
452 put of diff -u.
453 Note further that attachments are strongly preferred over inlined
455 patches. Attachments can be made by going to the Edit form of the
456 ticket immediately after its creation, and then using the left-most
457 button in the secondary navigation bar.
458
460 EBNF, LL(k), PEG, TDPL, context-free languages, expression, grammar,
461 matching, parser, parsing expression, parsing expression grammar, push
462 down automaton, recursive descent, state, top-down parsing languages,
463 transducer
464
466 Parsing and Grammars
467
469 Copyright (c) 2009 Andreas Kupries <andreas_kupries@users.sourceforge.net>
470tcllib 1.0.1 pt::pe(n)