1pt::peg::to::param(n) Parser Tools pt::peg::to::param(n)
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6
8 pt::peg::to::param - PEG Conversion. Write PARAM format
9
11 package require Tcl 8.5
12 package require pt::peg::to::param ?1?
14 package require pt::peg
16 package require pt::pe
18 pt::peg::to::param reset
20 pt::peg::to::param configure
22 pt::peg::to::param configure option
24 pt::peg::to::param configure option value...
26 pt::peg::to::param convert serial
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30
32 Are you lost ? Do you have trouble understanding this document ? In
33 that case please read the overview provided by the Introduction to
34 Parser Tools. This document is the entrypoint to the whole system the
35 current package is a part of.
36 This package implements the converter from parsing expression grammars
38 to PARAM markup.
39 It resides in the Export section of the Core Layer of Parser Tools, and
41 can be used either directly with the other packages of this layer, or
42 indirectly through the export manager provided by pt::peg::export. The
43 latter is intented for use in untrusted environments and done through
44 the corresponding export plugin pt::peg::export::param sitting between
45 converter and export manager.
46 IMAGE: arch_core_eplugins
48
50 The API provided by this package satisfies the specification of the
51 Converter API found in the Parser Tools Export API specification.
52 pt::peg::to::param reset
54 This command resets the configuration of the package to its de‐
55 fault settings.
56 pt::peg::to::param configure
58 This command returns a dictionary containing the current config‐
59 uration of the package.
60 pt::peg::to::param configure option
62 This command returns the current value of the specified configu‐
63 ration option of the package. For the set of legal options,
64 please read the section Options.
65 pt::peg::to::param configure option value...
67 This command sets the given configuration options of the pack‐
68 age, to the specified values. For the set of legal options,
69 please read the section Options.
70 pt::peg::to::param convert serial
72 This command takes the canonical serialization of a parsing ex‐
73 pression grammar, as specified in section PEG serialization for‐
74 mat, and contained in serial, and generates PARAM markup encod‐
75 ing the grammar, per the current package configuration. The
76 created string is then returned as the result of the command.
77
79 The converter to PARAM markup recognizes the following configuration
80 variables and changes its behaviour as they specify.
81 -template string
83 The value of this configuration variable is a string into which
84 to put the generated text and the other configuration settings.
85 The various locations for user-data are expected to be specified
86 with the placeholders listed below. The default value is
87 "@code@".
88 @user@ To be replaced with the value of the configuration vari‐
90 able -user.
91 @format@
93 To be replaced with the the constant PARAM.
94 @file@ To be replaced with the value of the configuration vari‐
96 able -file.
97 @name@ To be replaced with the value of the configuration vari‐
99 able -name.
100 @code@ To be replaced with the generated text.
102 -name string
104 The value of this configuration variable is the name of the
105 grammar for which the conversion is run. The default value is
106 a_pe_grammar.
107 -user string
109 The value of this configuration variable is the name of the user
110 for which the conversion is run. The default value is unknown.
111 -file string
113 The value of this configuration variable is the name of the file
114 or other entity from which the grammar came, for which the con‐
115 version is run. The default value is unknown.
116
118 The PARAM code representation of parsing expression grammars is assem‐
119 bler-like text using the instructions of the virtual machine documented
120 in the PackRat Machine Specification, plus a few more for control flow
121 (jump ok, jump fail, call symbol, return).
122 It is not really useful, except possibly as a tool demonstrating how a
124 grammar is compiled in general, without getting distracted by the inci‐
125 dentials of a framework, i.e. like the supporting C and Tcl code gener‐
126 ated by the other PARAM-derived formats.
127 It has no direct formal specification beyond what was said above.
129 EXAMPLE
131 Assuming the following PEG for simple mathematical expressions
132 PEG calculator (Expression)
134 Digit <- '0'/'1'/'2'/'3'/'4'/'5'/'6'/'7'/'8'/'9' ;
135 Sign <- '-' / '+' ;
136 Number <- Sign? Digit+ ;
137 Expression <- Term (AddOp Term)* ;
138 MulOp <- '*' / '/' ;
139 Term <- Factor (MulOp Factor)* ;
140 AddOp <- '+'/'-' ;
141 Factor <- '(' Expression ')' / Number ;
142 END;
143 one possible PARAM serialization for it is
146 # -*- text -*-
148 # Parsing Expression Grammar 'TEMPLATE'.
149 # Generated for unknown, from file 'TEST'
150 #
152 # Grammar Start Expression
153 #
154 <<MAIN>>:
156 call sym_Expression
157 halt
158 #
160 # value Symbol 'AddOp'
161 #
162 sym_AddOp:
164 # /
165 # '-'
166 # '+'
167 symbol_restore AddOp
169 found! jump found_7
170 loc_push
171 call choice_5
173 fail! value_clear
175 ok! value_leaf AddOp
176 symbol_save AddOp
177 error_nonterminal AddOp
178 loc_pop_discard
179 found_7:
181 ok! ast_value_push
182 return
183 choice_5:
185 # /
186 # '-'
187 # '+'
188 error_clear
190 loc_push
192 error_push
193 input_next "t -"
195 ok! test_char "-"
196 error_pop_merge
198 ok! jump oknoast_4
199 loc_pop_rewind
201 loc_push
202 error_push
203 input_next "t +"
205 ok! test_char "+"
206 error_pop_merge
208 ok! jump oknoast_4
209 loc_pop_rewind
211 status_fail
212 return
213 oknoast_4:
215 loc_pop_discard
216 return
217 #
218 # value Symbol 'Digit'
219 #
220 sym_Digit:
222 # /
223 # '0'
224 # '1'
225 # '2'
226 # '3'
227 # '4'
228 # '5'
229 # '6'
230 # '7'
231 # '8'
232 # '9'
233 symbol_restore Digit
235 found! jump found_22
236 loc_push
237 call choice_20
239 fail! value_clear
241 ok! value_leaf Digit
242 symbol_save Digit
243 error_nonterminal Digit
244 loc_pop_discard
245 found_22:
247 ok! ast_value_push
248 return
249 choice_20:
251 # /
252 # '0'
253 # '1'
254 # '2'
255 # '3'
256 # '4'
257 # '5'
258 # '6'
259 # '7'
260 # '8'
261 # '9'
262 error_clear
264 loc_push
266 error_push
267 input_next "t 0"
269 ok! test_char "0"
270 error_pop_merge
272 ok! jump oknoast_19
273 loc_pop_rewind
275 loc_push
276 error_push
277 input_next "t 1"
279 ok! test_char "1"
280 error_pop_merge
282 ok! jump oknoast_19
283 loc_pop_rewind
285 loc_push
286 error_push
287 input_next "t 2"
289 ok! test_char "2"
290 error_pop_merge
292 ok! jump oknoast_19
293 loc_pop_rewind
295 loc_push
296 error_push
297 input_next "t 3"
299 ok! test_char "3"
300 error_pop_merge
302 ok! jump oknoast_19
303 loc_pop_rewind
305 loc_push
306 error_push
307 input_next "t 4"
309 ok! test_char "4"
310 error_pop_merge
312 ok! jump oknoast_19
313 loc_pop_rewind
315 loc_push
316 error_push
317 input_next "t 5"
319 ok! test_char "5"
320 error_pop_merge
322 ok! jump oknoast_19
323 loc_pop_rewind
325 loc_push
326 error_push
327 input_next "t 6"
329 ok! test_char "6"
330 error_pop_merge
332 ok! jump oknoast_19
333 loc_pop_rewind
335 loc_push
336 error_push
337 input_next "t 7"
339 ok! test_char "7"
340 error_pop_merge
342 ok! jump oknoast_19
343 loc_pop_rewind
345 loc_push
346 error_push
347 input_next "t 8"
349 ok! test_char "8"
350 error_pop_merge
352 ok! jump oknoast_19
353 loc_pop_rewind
355 loc_push
356 error_push
357 input_next "t 9"
359 ok! test_char "9"
360 error_pop_merge
362 ok! jump oknoast_19
363 loc_pop_rewind
365 status_fail
366 return
367 oknoast_19:
369 loc_pop_discard
370 return
371 #
372 # value Symbol 'Expression'
373 #
374 sym_Expression:
376 # /
377 # x
378 # '\('
379 # (Expression)
380 # '\)'
381 # x
382 # (Factor)
383 # *
384 # x
385 # (MulOp)
386 # (Factor)
387 symbol_restore Expression
389 found! jump found_46
390 loc_push
391 ast_push
392 call choice_44
394 fail! value_clear
396 ok! value_reduce Expression
397 symbol_save Expression
398 error_nonterminal Expression
399 ast_pop_rewind
400 loc_pop_discard
401 found_46:
403 ok! ast_value_push
404 return
405 choice_44:
407 # /
408 # x
409 # '\('
410 # (Expression)
411 # '\)'
412 # x
413 # (Factor)
414 # *
415 # x
416 # (MulOp)
417 # (Factor)
418 error_clear
420 ast_push
422 loc_push
423 error_push
424 call sequence_27
426 error_pop_merge
428 ok! jump ok_43
429 ast_pop_rewind
431 loc_pop_rewind
432 ast_push
433 loc_push
434 error_push
435 call sequence_40
437 error_pop_merge
439 ok! jump ok_43
440 ast_pop_rewind
442 loc_pop_rewind
443 status_fail
444 return
445 ok_43:
447 ast_pop_discard
448 loc_pop_discard
449 return
450 sequence_27:
452 # x
453 # '\('
454 # (Expression)
455 # '\)'
456 loc_push
458 error_clear
459 error_push
461 input_next "t ("
463 ok! test_char "("
464 error_pop_merge
466 fail! jump failednoast_29
467 ast_push
468 error_push
469 call sym_Expression
471 error_pop_merge
473 fail! jump failed_28
474 error_push
475 input_next "t )"
477 ok! test_char ")"
478 error_pop_merge
480 fail! jump failed_28
481 ast_pop_discard
483 loc_pop_discard
484 return
485 failed_28:
487 ast_pop_rewind
488 failednoast_29:
490 loc_pop_rewind
491 return
492 sequence_40:
494 # x
495 # (Factor)
496 # *
497 # x
498 # (MulOp)
499 # (Factor)
500 ast_push
502 loc_push
503 error_clear
504 error_push
506 call sym_Factor
508 error_pop_merge
510 fail! jump failed_41
511 error_push
512 call kleene_37
514 error_pop_merge
516 fail! jump failed_41
517 ast_pop_discard
519 loc_pop_discard
520 return
521 failed_41:
523 ast_pop_rewind
524 loc_pop_rewind
525 return
526 kleene_37:
528 # *
529 # x
530 # (MulOp)
531 # (Factor)
532 loc_push
534 error_push
535 call sequence_34
537 error_pop_merge
539 fail! jump failed_38
540 loc_pop_discard
541 jump kleene_37
542 failed_38:
544 loc_pop_rewind
545 status_ok
546 return
547 sequence_34:
549 # x
550 # (MulOp)
551 # (Factor)
552 ast_push
554 loc_push
555 error_clear
556 error_push
558 call sym_MulOp
560 error_pop_merge
562 fail! jump failed_35
563 error_push
564 call sym_Factor
566 error_pop_merge
568 fail! jump failed_35
569 ast_pop_discard
571 loc_pop_discard
572 return
573 failed_35:
575 ast_pop_rewind
576 loc_pop_rewind
577 return
578 #
579 # value Symbol 'Factor'
580 #
581 sym_Factor:
583 # x
584 # (Term)
585 # *
586 # x
587 # (AddOp)
588 # (Term)
589 symbol_restore Factor
591 found! jump found_60
592 loc_push
593 ast_push
594 call sequence_57
596 fail! value_clear
598 ok! value_reduce Factor
599 symbol_save Factor
600 error_nonterminal Factor
601 ast_pop_rewind
602 loc_pop_discard
603 found_60:
605 ok! ast_value_push
606 return
607 sequence_57:
609 # x
610 # (Term)
611 # *
612 # x
613 # (AddOp)
614 # (Term)
615 ast_push
617 loc_push
618 error_clear
619 error_push
621 call sym_Term
623 error_pop_merge
625 fail! jump failed_58
626 error_push
627 call kleene_54
629 error_pop_merge
631 fail! jump failed_58
632 ast_pop_discard
634 loc_pop_discard
635 return
636 failed_58:
638 ast_pop_rewind
639 loc_pop_rewind
640 return
641 kleene_54:
643 # *
644 # x
645 # (AddOp)
646 # (Term)
647 loc_push
649 error_push
650 call sequence_51
652 error_pop_merge
654 fail! jump failed_55
655 loc_pop_discard
656 jump kleene_54
657 failed_55:
659 loc_pop_rewind
660 status_ok
661 return
662 sequence_51:
664 # x
665 # (AddOp)
666 # (Term)
667 ast_push
669 loc_push
670 error_clear
671 error_push
673 call sym_AddOp
675 error_pop_merge
677 fail! jump failed_52
678 error_push
679 call sym_Term
681 error_pop_merge
683 fail! jump failed_52
684 ast_pop_discard
686 loc_pop_discard
687 return
688 failed_52:
690 ast_pop_rewind
691 loc_pop_rewind
692 return
693 #
694 # value Symbol 'MulOp'
695 #
696 sym_MulOp:
698 # /
699 # '*'
700 # '/'
701 symbol_restore MulOp
703 found! jump found_67
704 loc_push
705 call choice_65
707 fail! value_clear
709 ok! value_leaf MulOp
710 symbol_save MulOp
711 error_nonterminal MulOp
712 loc_pop_discard
713 found_67:
715 ok! ast_value_push
716 return
717 choice_65:
719 # /
720 # '*'
721 # '/'
722 error_clear
724 loc_push
726 error_push
727 input_next "t *"
729 ok! test_char "*"
730 error_pop_merge
732 ok! jump oknoast_64
733 loc_pop_rewind
735 loc_push
736 error_push
737 input_next "t /"
739 ok! test_char "/"
740 error_pop_merge
742 ok! jump oknoast_64
743 loc_pop_rewind
745 status_fail
746 return
747 oknoast_64:
749 loc_pop_discard
750 return
751 #
752 # value Symbol 'Number'
753 #
754 sym_Number:
756 # x
757 # ?
758 # (Sign)
759 # +
760 # (Digit)
761 symbol_restore Number
763 found! jump found_80
764 loc_push
765 ast_push
766 call sequence_77
768 fail! value_clear
770 ok! value_reduce Number
771 symbol_save Number
772 error_nonterminal Number
773 ast_pop_rewind
774 loc_pop_discard
775 found_80:
777 ok! ast_value_push
778 return
779 sequence_77:
781 # x
782 # ?
783 # (Sign)
784 # +
785 # (Digit)
786 ast_push
788 loc_push
789 error_clear
790 error_push
792 call optional_70
794 error_pop_merge
796 fail! jump failed_78
797 error_push
798 call poskleene_73
800 error_pop_merge
802 fail! jump failed_78
803 ast_pop_discard
805 loc_pop_discard
806 return
807 failed_78:
809 ast_pop_rewind
810 loc_pop_rewind
811 return
812 optional_70:
814 # ?
815 # (Sign)
816 loc_push
818 error_push
819 call sym_Sign
821 error_pop_merge
823 fail! loc_pop_rewind
824 ok! loc_pop_discard
825 status_ok
826 return
827 poskleene_73:
829 # +
830 # (Digit)
831 loc_push
833 call sym_Digit
835 fail! jump failed_74
837 loop_75:
839 loc_pop_discard
840 loc_push
841 error_push
842 call sym_Digit
844 error_pop_merge
846 ok! jump loop_75
847 status_ok
848 failed_74:
850 loc_pop_rewind
851 return
852 #
853 # value Symbol 'Sign'
854 #
855 sym_Sign:
857 # /
858 # '-'
859 # '+'
860 symbol_restore Sign
862 found! jump found_86
863 loc_push
864 call choice_5
866 fail! value_clear
868 ok! value_leaf Sign
869 symbol_save Sign
870 error_nonterminal Sign
871 loc_pop_discard
872 found_86:
874 ok! ast_value_push
875 return
876 #
877 # value Symbol 'Term'
878 #
879 sym_Term:
881 # (Number)
882 symbol_restore Term
884 found! jump found_89
885 loc_push
886 ast_push
887 call sym_Number
889 fail! value_clear
891 ok! value_reduce Term
892 symbol_save Term
893 error_nonterminal Term
894 ast_pop_rewind
895 loc_pop_discard
896 found_89:
898 ok! ast_value_push
899 return
900 #
902 #
903
906 Here we specify the format used by the Parser Tools to serialize Pars‐
907 ing Expression Grammars as immutable values for transport, comparison,
908 etc.
909 We distinguish between regular and canonical serializations. While a
911 PEG may have more than one regular serialization only exactly one of
912 them will be canonical.
913 regular serialization
915 [1] The serialization of any PEG is a nested Tcl dictionary.
917 [2] This dictionary holds a single key, pt::grammar::peg, and
919 its value. This value holds the contents of the grammar.
920 [3] The contents of the grammar are a Tcl dictionary holding
922 the set of nonterminal symbols and the starting expres‐
923 sion. The relevant keys and their values are
924 rules The value is a Tcl dictionary whose keys are the
926 names of the nonterminal symbols known to the
927 grammar.
928 [1] Each nonterminal symbol may occur only
930 once.
931 [2] The empty string is not a legal nonterminal
933 symbol.
934 [3] The value for each symbol is a Tcl dictio‐
936 nary itself. The relevant keys and their
937 values in this dictionary are
938 is The value is the serialization of
940 the parsing expression describing
941 the symbols sentennial structure, as
942 specified in the section PE serial‐
943 ization format.
944 mode The value can be one of three values
946 specifying how a parser should han‐
947 dle the semantic value produced by
948 the symbol.
949 value The semantic value of the
951 nonterminal symbol is an ab‐
952 stract syntax tree consisting
953 of a single node node for the
954 nonterminal itself, which has
955 the ASTs of the symbol's
956 right hand side as its chil‐
957 dren.
958 leaf The semantic value of the
960 nonterminal symbol is an ab‐
961 stract syntax tree consisting
962 of a single node node for the
963 nonterminal, without any
964 children. Any ASTs generated
965 by the symbol's right hand
966 side are discarded.
967 void The nonterminal has no seman‐
969 tic value. Any ASTs generated
970 by the symbol's right hand
971 side are discarded (as well).
972 start The value is the serialization of the start pars‐
974 ing expression of the grammar, as specified in the
975 section PE serialization format.
976 [4] The terminal symbols of the grammar are specified implic‐
978 itly as the set of all terminal symbols used in the start
979 expression and on the RHS of the grammar rules.
980 canonical serialization
982 The canonical serialization of a grammar has the format as spec‐
983 ified in the previous item, and then additionally satisfies the
984 constraints below, which make it unique among all the possible
985 serializations of this grammar.
986 [1] The keys found in all the nested Tcl dictionaries are
988 sorted in ascending dictionary order, as generated by
989 Tcl's builtin command lsort -increasing -dict.
990 [2] The string representation of the value is the canonical
992 representation of a Tcl dictionary. I.e. it does not con‐
993 tain superfluous whitespace.
994 EXAMPLE
996 Assuming the following PEG for simple mathematical expressions
997 PEG calculator (Expression)
999 Digit <- '0'/'1'/'2'/'3'/'4'/'5'/'6'/'7'/'8'/'9' ;
1000 Sign <- '-' / '+' ;
1001 Number <- Sign? Digit+ ;
1002 Expression <- Term (AddOp Term)* ;
1003 MulOp <- '*' / '/' ;
1004 Term <- Factor (MulOp Factor)* ;
1005 AddOp <- '+'/'-' ;
1006 Factor <- '(' Expression ')' / Number ;
1007 END;
1008 then its canonical serialization (except for whitespace) is
1011 pt::grammar::peg {
1013 rules {
1014 AddOp {is {/ {t -} {t +}} mode value}
1015 Digit {is {/ {t 0} {t 1} {t 2} {t 3} {t 4} {t 5} {t 6} {t 7} {t 8} {t 9}} mode value}
1016 Expression {is {x {n Term} {* {x {n AddOp} {n Term}}}} mode value}
1017 Factor {is {/ {x {t (} {n Expression} {t )}} {n Number}} mode value}
1018 MulOp {is {/ {t *} {t /}} mode value}
1019 Number {is {x {? {n Sign}} {+ {n Digit}}} mode value}
1020 Sign {is {/ {t -} {t +}} mode value}
1021 Term {is {x {n Factor} {* {x {n MulOp} {n Factor}}}} mode value}
1022 }
1023 start {n Expression}
1024 }
1025
1028 Here we specify the format used by the Parser Tools to serialize Pars‐
1029 ing Expressions as immutable values for transport, comparison, etc.
1030 We distinguish between regular and canonical serializations. While a
1032 parsing expression may have more than one regular serialization only
1033 exactly one of them will be canonical.
1034 Regular serialization
1036 Atomic Parsing Expressions
1038 [1] The string epsilon is an atomic parsing expres‐
1040 sion. It matches the empty string.
1041 [2] The string dot is an atomic parsing expression. It
1043 matches any character.
1044 [3] The string alnum is an atomic parsing expression.
1046 It matches any Unicode alphabet or digit charac‐
1047 ter. This is a custom extension of PEs based on
1048 Tcl's builtin command string is.
1049 [4] The string alpha is an atomic parsing expression.
1051 It matches any Unicode alphabet character. This is
1052 a custom extension of PEs based on Tcl's builtin
1053 command string is.
1054 [5] The string ascii is an atomic parsing expression.
1056 It matches any Unicode character below U0080. This
1057 is a custom extension of PEs based on Tcl's
1058 builtin command string is.
1059 [6] The string control is an atomic parsing expres‐
1061 sion. It matches any Unicode control character.
1062 This is a custom extension of PEs based on Tcl's
1063 builtin command string is.
1064 [7] The string digit is an atomic parsing expression.
1066 It matches any Unicode digit character. Note that
1067 this includes characters outside of the [0..9]
1068 range. This is a custom extension of PEs based on
1069 Tcl's builtin command string is.
1070 [8] The string graph is an atomic parsing expression.
1072 It matches any Unicode printing character, except
1073 for space. This is a custom extension of PEs based
1074 on Tcl's builtin command string is.
1075 [9] The string lower is an atomic parsing expression.
1077 It matches any Unicode lower-case alphabet charac‐
1078 ter. This is a custom extension of PEs based on
1079 Tcl's builtin command string is.
1080 [10] The string print is an atomic parsing expression.
1082 It matches any Unicode printing character, includ‐
1083 ing space. This is a custom extension of PEs based
1084 on Tcl's builtin command string is.
1085 [11] The string punct is an atomic parsing expression.
1087 It matches any Unicode punctuation character. This
1088 is a custom extension of PEs based on Tcl's
1089 builtin command string is.
1090 [12] The string space is an atomic parsing expression.
1092 It matches any Unicode space character. This is a
1093 custom extension of PEs based on Tcl's builtin
1094 command string is.
1095 [13] The string upper is an atomic parsing expression.
1097 It matches any Unicode upper-case alphabet charac‐
1098 ter. This is a custom extension of PEs based on
1099 Tcl's builtin command string is.
1100 [14] The string wordchar is an atomic parsing expres‐
1102 sion. It matches any Unicode word character. This
1103 is any alphanumeric character (see alnum), and any
1104 connector punctuation characters (e.g. under‐
1105 score). This is a custom extension of PEs based on
1106 Tcl's builtin command string is.
1107 [15] The string xdigit is an atomic parsing expression.
1109 It matches any hexadecimal digit character. This
1110 is a custom extension of PEs based on Tcl's
1111 builtin command string is.
1112 [16] The string ddigit is an atomic parsing expression.
1114 It matches any decimal digit character. This is a
1115 custom extension of PEs based on Tcl's builtin
1116 command regexp.
1117 [17] The expression [list t x] is an atomic parsing ex‐
1119 pression. It matches the terminal string x.
1120 [18] The expression [list n A] is an atomic parsing ex‐
1122 pression. It matches the nonterminal A.
1123 Combined Parsing Expressions
1125 [1] For parsing expressions e1, e2, ... the result of
1127 [list / e1 e2 ... ] is a parsing expression as
1128 well. This is the ordered choice, aka prioritized
1129 choice.
1130 [2] For parsing expressions e1, e2, ... the result of
1132 [list x e1 e2 ... ] is a parsing expression as
1133 well. This is the sequence.
1134 [3] For a parsing expression e the result of [list *
1136 e] is a parsing expression as well. This is the
1137 kleene closure, describing zero or more repeti‐
1138 tions.
1139 [4] For a parsing expression e the result of [list +
1141 e] is a parsing expression as well. This is the
1142 positive kleene closure, describing one or more
1143 repetitions.
1144 [5] For a parsing expression e the result of [list &
1146 e] is a parsing expression as well. This is the
1147 and lookahead predicate.
1148 [6] For a parsing expression e the result of [list !
1150 e] is a parsing expression as well. This is the
1151 not lookahead predicate.
1152 [7] For a parsing expression e the result of [list ?
1154 e] is a parsing expression as well. This is the
1155 optional input.
1156 Canonical serialization
1158 The canonical serialization of a parsing expression has the for‐
1159 mat as specified in the previous item, and then additionally
1160 satisfies the constraints below, which make it unique among all
1161 the possible serializations of this parsing expression.
1162 [1] The string representation of the value is the canonical
1164 representation of a pure Tcl list. I.e. it does not con‐
1165 tain superfluous whitespace.
1166 [2] Terminals are not encoded as ranges (where start and end
1168 of the range are identical).
1169 EXAMPLE
1171 Assuming the parsing expression shown on the right-hand side of the
1172 rule
1173 Expression <- Term (AddOp Term)*
1175 then its canonical serialization (except for whitespace) is
1178 {x {n Term} {* {x {n AddOp} {n Term}}}}
1180
1183 This document, and the package it describes, will undoubtedly contain
1184 bugs and other problems. Please report such in the category pt of the
1185 Tcllib Trackers [http://core.tcl.tk/tcllib/reportlist]. Please also
1186 report any ideas for enhancements you may have for either package
1187 and/or documentation.
1188 When proposing code changes, please provide unified diffs, i.e the out‐
1190 put of diff -u.
1191 Note further that attachments are strongly preferred over inlined
1193 patches. Attachments can be made by going to the Edit form of the
1194 ticket immediately after its creation, and then using the left-most
1195 button in the secondary navigation bar.
1196
1198 EBNF, LL(k), PARAM, PEG, TDPL, context-free languages, conversion, ex‐
1199 pression, format conversion, grammar, matching, parser, parsing expres‐
1200 sion, parsing expression grammar, push down automaton, recursive de‐
1201 scent, serialization, state, top-down parsing languages, transducer
1202
1204 Parsing and Grammars
1205
1207 Copyright (c) 2009 Andreas Kupries <andreas_kupries@users.sourceforge.net>
1208tcllib 1 pt::peg::to::param(n)