1pt::peg::from::json(n)           Parser Tools           pt::peg::from::json(n)
2
3
4
5______________________________________________________________________________
6

NAME

8       pt::peg::from::json - PEG Conversion. Read JSON format
9

SYNOPSIS

11       package require Tcl  8.5
12
13       package require pt::peg::from::json  ?1?
14
15       package require pt::peg
16
17       package require json
18
19       pt::peg::from::json convert text
20
21______________________________________________________________________________
22

DESCRIPTION

24       Are  you  lost ?  Do you have trouble understanding this document ?  In
25       that case please read the overview  provided  by  the  Introduction  to
26       Parser  Tools.  This document is the entrypoint to the whole system the
27       current package is a part of.
28
29       This package implements the converter from JSON markup to  parsing  ex‐
30       pression grammars.
31
32       It resides in the Import section of the Core Layer of Parser Tools, and
33       can be used either directly with the other packages of this  layer,  or
34       indirectly  through the import manager provided by pt::peg::import. The
35       latter is intented for use in untrusted environments and  done  through
36       the  corresponding  import plugin pt::peg::import::json sitting between
37       converter and import manager.
38
39       IMAGE: arch_core_iplugins
40

API

42       The API provided by this package satisfies  the  specification  of  the
43       Converter API found in the Parser Tools Import API specification.
44
45       pt::peg::from::json convert text
46              This command takes the JSON markup encoding a parsing expression
47              grammar and contained in text, and generates the canonical seri‐
48              alization  of  said grammar, as specified in section PEG serial‐
49              ization format.  The created value is then returned as  the  re‐
50              sult of the command.
51

JSON GRAMMAR EXCHANGE FORMAT

53       The  json  format for parsing expression grammars was written as a data
54       exchange format not bound to Tcl. It was defined to allow the  exchange
55       of  grammars  with  PackRat/PEG  based parser generators for other lan‐
56       guages.
57
58       It is formally specified by the rules below:
59
60       [1]    The JSON of any PEG is a JSON object.
61
62       [2]    This object holds a single key, pt::grammar::peg, and its value.
63              This value holds the contents of the grammar.
64
65       [3]    The contents of the grammar are a JSON object holding the set of
66              nonterminal symbols and the starting  expression.  The  relevant
67              keys and their values are
68
69              rules  The  value  is  a JSON object whose keys are the names of
70                     the nonterminal symbols known to the grammar.
71
72                     [1]    Each nonterminal symbol may occur only once.
73
74                     [2]    The empty string is not a legal  nonterminal  sym‐
75                            bol.
76
77                     [3]    The value for each symbol is a JSON object itself.
78                            The relevant keys and their values in this dictio‐
79                            nary are
80
81                            is     The  value is a JSON string holding the Tcl
82                                   serialization of the parsing expression de‐
83                                   scribing  the symbols sentennial structure,
84                                   as specified in the section  PE  serializa‐
85                                   tion format.
86
87                            mode   The  value is a JSON holding holding one of
88                                   three values specifying how a parser should
89                                   handle  the  semantic value produced by the
90                                   symbol.
91
92                                   value  The semantic value of the  nontermi‐
93                                          nal  symbol  is  an  abstract syntax
94                                          tree consisting  of  a  single  node
95                                          node  for  the  nonterminal  itself,
96                                          which has the ASTs of  the  symbol's
97                                          right hand side as its children.
98
99                                   leaf   The  semantic value of the nontermi‐
100                                          nal symbol  is  an  abstract  syntax
101                                          tree  consisting  of  a  single node
102                                          node for  the  nonterminal,  without
103                                          any  children. Any ASTs generated by
104                                          the symbol's  right  hand  side  are
105                                          discarded.
106
107                                   void   The   nonterminal  has  no  semantic
108                                          value. Any  ASTs  generated  by  the
109                                          symbol's  right  hand  side are dis‐
110                                          carded (as well).
111
112              start  The value is a JSON string holding the Tcl  serialization
113                     of the start parsing expression of the grammar, as speci‐
114                     fied in the section PE serialization format.
115
116       [4]    The terminal symbols of the grammar are specified implicitly  as
117              the set of all terminal symbols used in the start expression and
118              on the RHS of the grammar rules.
119
120       As an aside to the advanced reader, this is pretty much the same as the
121       Tcl  serialization  of PE grammars, as specified in section PEG serial‐
122       ization format, except that the Tcl dictionaries and lists of that for‐
123       mat are mapped to JSON objects and arrays. Only the parsing expressions
124       themselves are not translated further, but kept as  JSON  strings  con‐
125       taining  a  nested  Tcl list, and there is no concept of canonicity for
126       the JSON either.
127
128   EXAMPLE
129       Assuming the following PEG for simple mathematical expressions
130
131              PEG calculator (Expression)
132                  Digit      <- '0'/'1'/'2'/'3'/'4'/'5'/'6'/'7'/'8'/'9'       ;
133                  Sign       <- '-' / '+'                                     ;
134                  Number     <- Sign? Digit+                                  ;
135                  Expression <- Term (AddOp Term)*                            ;
136                  MulOp      <- '*' / '/'                                     ;
137                  Term       <- Factor (MulOp Factor)*                        ;
138                  AddOp      <- '+'/'-'                                       ;
139                  Factor     <- '(' Expression ')' / Number                   ;
140              END;
141
142
143       a JSON serialization for it is
144
145              {
146                  "pt::grammar::peg" : {
147                      "rules" : {
148                          "AddOp"     : {
149                              "is"   : "\/ {t -} {t +}",
150                              "mode" : "value"
151                          },
152                          "Digit"     : {
153                              "is"   : "\/ {t 0} {t 1} {t 2} {t 3} {t 4} {t 5} {t 6} {t 7} {t 8} {t 9}",
154                              "mode" : "value"
155                          },
156                          "Expression" : {
157                              "is"   : "\/ {x {t (} {n Expression} {t )}} {x {n Factor} {* {x {n MulOp} {n Factor}}}}",
158                              "mode" : "value"
159                          },
160                          "Factor"    : {
161                              "is"   : "x {n Term} {* {x {n AddOp} {n Term}}}",
162                              "mode" : "value"
163                          },
164                          "MulOp"     : {
165                              "is"   : "\/ {t *} {t \/}",
166                              "mode" : "value"
167                          },
168                          "Number"    : {
169                              "is"   : "x {? {n Sign}} {+ {n Digit}}",
170                              "mode" : "value"
171                          },
172                          "Sign"      : {
173                              "is"   : "\/ {t -} {t +}",
174                              "mode" : "value"
175                          },
176                          "Term"      : {
177                              "is"   : "n Number",
178                              "mode" : "value"
179                          }
180                      },
181                      "start" : "n Expression"
182                  }
183              }
184
185
186       and a Tcl serialization of the same is
187
188              pt::grammar::peg {
189                  rules {
190                      AddOp      {is {/ {t -} {t +}}                                                                mode value}
191                      Digit      {is {/ {t 0} {t 1} {t 2} {t 3} {t 4} {t 5} {t 6} {t 7} {t 8} {t 9}}                mode value}
192                      Expression {is {x {n Term} {* {x {n AddOp} {n Term}}}}                                        mode value}
193                      Factor     {is {/ {x {t (} {n Expression} {t )}} {n Number}}                                  mode value}
194                      MulOp      {is {/ {t *} {t /}}                                                                mode value}
195                      Number     {is {x {? {n Sign}} {+ {n Digit}}}                                                 mode value}
196                      Sign       {is {/ {t -} {t +}}                                                                mode value}
197                      Term       {is {x {n Factor} {* {x {n MulOp} {n Factor}}}}                                    mode value}
198                  }
199                  start {n Expression}
200              }
201
202
203       The similarity of the latter to the JSON should be quite obvious.
204

PEG SERIALIZATION FORMAT

206       Here we specify the format used by the Parser Tools to serialize  Pars‐
207       ing  Expression Grammars as immutable values for transport, comparison,
208       etc.
209
210       We distinguish between regular and canonical serializations.   While  a
211       PEG  may  have  more than one regular serialization only exactly one of
212       them will be canonical.
213
214       regular serialization
215
216              [1]    The serialization of any PEG is a nested Tcl dictionary.
217
218              [2]    This dictionary holds a single key, pt::grammar::peg, and
219                     its value. This value holds the contents of the grammar.
220
221              [3]    The  contents of the grammar are a Tcl dictionary holding
222                     the set of nonterminal symbols and the  starting  expres‐
223                     sion. The relevant keys and their values are
224
225                     rules  The  value  is a Tcl dictionary whose keys are the
226                            names of the  nonterminal  symbols  known  to  the
227                            grammar.
228
229                            [1]    Each  nonterminal  symbol  may  occur  only
230                                   once.
231
232                            [2]    The empty string is not a legal nonterminal
233                                   symbol.
234
235                            [3]    The  value for each symbol is a Tcl dictio‐
236                                   nary itself. The relevant  keys  and  their
237                                   values in this dictionary are
238
239                                   is     The  value  is  the serialization of
240                                          the  parsing  expression  describing
241                                          the symbols sentennial structure, as
242                                          specified in the section PE  serial‐
243                                          ization format.
244
245                                   mode   The value can be one of three values
246                                          specifying how a parser should  han‐
247                                          dle  the  semantic value produced by
248                                          the symbol.
249
250                                          value  The  semantic  value  of  the
251                                                 nonterminal  symbol is an ab‐
252                                                 stract syntax tree consisting
253                                                 of a single node node for the
254                                                 nonterminal itself, which has
255                                                 the   ASTs  of  the  symbol's
256                                                 right hand side as its  chil‐
257                                                 dren.
258
259                                          leaf   The  semantic  value  of  the
260                                                 nonterminal symbol is an  ab‐
261                                                 stract syntax tree consisting
262                                                 of a single node node for the
263                                                 nonterminal,    without   any
264                                                 children. Any ASTs  generated
265                                                 by  the  symbol's  right hand
266                                                 side are discarded.
267
268                                          void   The nonterminal has no seman‐
269                                                 tic value. Any ASTs generated
270                                                 by the  symbol's  right  hand
271                                                 side are discarded (as well).
272
273                     start  The  value is the serialization of the start pars‐
274                            ing expression of the grammar, as specified in the
275                            section PE serialization format.
276
277              [4]    The terminal symbols of the grammar are specified implic‐
278                     itly as the set of all terminal symbols used in the start
279                     expression and on the RHS of the grammar rules.
280
281       canonical serialization
282              The canonical serialization of a grammar has the format as spec‐
283              ified in the previous item, and then additionally satisfies  the
284              constraints  below,  which make it unique among all the possible
285              serializations of this grammar.
286
287              [1]    The keys found in all the  nested  Tcl  dictionaries  are
288                     sorted  in  ascending  dictionary  order, as generated by
289                     Tcl's builtin command lsort -increasing -dict.
290
291              [2]    The string representation of the value is  the  canonical
292                     representation of a Tcl dictionary. I.e. it does not con‐
293                     tain superfluous whitespace.
294
295   EXAMPLE
296       Assuming the following PEG for simple mathematical expressions
297
298              PEG calculator (Expression)
299                  Digit      <- '0'/'1'/'2'/'3'/'4'/'5'/'6'/'7'/'8'/'9'       ;
300                  Sign       <- '-' / '+'                                     ;
301                  Number     <- Sign? Digit+                                  ;
302                  Expression <- Term (AddOp Term)*                            ;
303                  MulOp      <- '*' / '/'                                     ;
304                  Term       <- Factor (MulOp Factor)*                        ;
305                  AddOp      <- '+'/'-'                                       ;
306                  Factor     <- '(' Expression ')' / Number                   ;
307              END;
308
309
310       then its canonical serialization (except for whitespace) is
311
312              pt::grammar::peg {
313                  rules {
314                      AddOp      {is {/ {t -} {t +}}                                                                mode value}
315                      Digit      {is {/ {t 0} {t 1} {t 2} {t 3} {t 4} {t 5} {t 6} {t 7} {t 8} {t 9}}                mode value}
316                      Expression {is {x {n Term} {* {x {n AddOp} {n Term}}}}                                        mode value}
317                      Factor     {is {/ {x {t (} {n Expression} {t )}} {n Number}}                                  mode value}
318                      MulOp      {is {/ {t *} {t /}}                                                                mode value}
319                      Number     {is {x {? {n Sign}} {+ {n Digit}}}                                                 mode value}
320                      Sign       {is {/ {t -} {t +}}                                                                mode value}
321                      Term       {is {x {n Factor} {* {x {n MulOp} {n Factor}}}}                                    mode value}
322                  }
323                  start {n Expression}
324              }
325
326

PE SERIALIZATION FORMAT

328       Here we specify the format used by the Parser Tools to serialize  Pars‐
329       ing Expressions as immutable values for transport, comparison, etc.
330
331       We  distinguish  between regular and canonical serializations.  While a
332       parsing expression may have more than one  regular  serialization  only
333       exactly one of them will be canonical.
334
335       Regular serialization
336
337              Atomic Parsing Expressions
338
339                     [1]    The  string  epsilon  is an atomic parsing expres‐
340                            sion. It matches the empty string.
341
342                     [2]    The string dot is an atomic parsing expression. It
343                            matches any character.
344
345                     [3]    The  string alnum is an atomic parsing expression.
346                            It matches any Unicode alphabet or  digit  charac‐
347                            ter.  This  is  a custom extension of PEs based on
348                            Tcl's builtin command string is.
349
350                     [4]    The string alpha is an atomic parsing  expression.
351                            It matches any Unicode alphabet character. This is
352                            a custom extension of PEs based on  Tcl's  builtin
353                            command string is.
354
355                     [5]    The  string ascii is an atomic parsing expression.
356                            It matches any Unicode character below U0080. This
357                            is  a  custom  extension  of  PEs  based  on Tcl's
358                            builtin command string is.
359
360                     [6]    The string control is an  atomic  parsing  expres‐
361                            sion.  It  matches  any Unicode control character.
362                            This is a custom extension of PEs based  on  Tcl's
363                            builtin command string is.
364
365                     [7]    The  string digit is an atomic parsing expression.
366                            It matches any Unicode digit character. Note  that
367                            this  includes  characters  outside  of the [0..9]
368                            range. This is a custom extension of PEs based  on
369                            Tcl's builtin command string is.
370
371                     [8]    The  string graph is an atomic parsing expression.
372                            It matches any Unicode printing character,  except
373                            for space. This is a custom extension of PEs based
374                            on Tcl's builtin command string is.
375
376                     [9]    The string lower is an atomic parsing  expression.
377                            It matches any Unicode lower-case alphabet charac‐
378                            ter. This is a custom extension of  PEs  based  on
379                            Tcl's builtin command string is.
380
381                     [10]   The  string print is an atomic parsing expression.
382                            It matches any Unicode printing character, includ‐
383                            ing space. This is a custom extension of PEs based
384                            on Tcl's builtin command string is.
385
386                     [11]   The string punct is an atomic parsing  expression.
387                            It matches any Unicode punctuation character. This
388                            is a  custom  extension  of  PEs  based  on  Tcl's
389                            builtin command string is.
390
391                     [12]   The  string space is an atomic parsing expression.
392                            It matches any Unicode space character. This is  a
393                            custom  extension  of  PEs  based on Tcl's builtin
394                            command string is.
395
396                     [13]   The string upper is an atomic parsing  expression.
397                            It matches any Unicode upper-case alphabet charac‐
398                            ter. This is a custom extension of  PEs  based  on
399                            Tcl's builtin command string is.
400
401                     [14]   The  string  wordchar is an atomic parsing expres‐
402                            sion. It matches any Unicode word character.  This
403                            is any alphanumeric character (see alnum), and any
404                            connector  punctuation  characters  (e.g.   under‐
405                            score). This is a custom extension of PEs based on
406                            Tcl's builtin command string is.
407
408                     [15]   The string xdigit is an atomic parsing expression.
409                            It  matches  any hexadecimal digit character. This
410                            is a  custom  extension  of  PEs  based  on  Tcl's
411                            builtin command string is.
412
413                     [16]   The string ddigit is an atomic parsing expression.
414                            It matches any decimal digit character. This is  a
415                            custom  extension  of  PEs  based on Tcl's builtin
416                            command regexp.
417
418                     [17]   The expression [list t x] is an atomic parsing ex‐
419                            pression. It matches the terminal string x.
420
421                     [18]   The expression [list n A] is an atomic parsing ex‐
422                            pression. It matches the nonterminal A.
423
424              Combined Parsing Expressions
425
426                     [1]    For parsing expressions e1, e2, ... the result  of
427                            [list  /  e1  e2  ... ] is a parsing expression as
428                            well.  This is the ordered choice, aka prioritized
429                            choice.
430
431                     [2]    For  parsing expressions e1, e2, ... the result of
432                            [list x e1 e2 ... ] is  a  parsing  expression  as
433                            well.  This is the sequence.
434
435                     [3]    For  a  parsing expression e the result of [list *
436                            e] is a parsing expression as well.  This  is  the
437                            kleene  closure,  describing  zero or more repeti‐
438                            tions.
439
440                     [4]    For a parsing expression e the result of  [list  +
441                            e]  is  a parsing expression as well.  This is the
442                            positive kleene closure, describing  one  or  more
443                            repetitions.
444
445                     [5]    For  a  parsing expression e the result of [list &
446                            e] is a parsing expression as well.  This  is  the
447                            and lookahead predicate.
448
449                     [6]    For  a  parsing expression e the result of [list !
450                            e] is a parsing expression as well.  This  is  the
451                            not lookahead predicate.
452
453                     [7]    For  a  parsing expression e the result of [list ?
454                            e] is a parsing expression as well.  This  is  the
455                            optional input.
456
457       Canonical serialization
458              The canonical serialization of a parsing expression has the for‐
459              mat as specified in the previous  item,  and  then  additionally
460              satisfies  the constraints below, which make it unique among all
461              the possible serializations of this parsing expression.
462
463              [1]    The string representation of the value is  the  canonical
464                     representation  of a pure Tcl list. I.e. it does not con‐
465                     tain superfluous whitespace.
466
467              [2]    Terminals are not encoded as ranges (where start and  end
468                     of the range are identical).
469
470   EXAMPLE
471       Assuming  the  parsing  expression  shown on the right-hand side of the
472       rule
473
474                  Expression <- Term (AddOp Term)*
475
476
477       then its canonical serialization (except for whitespace) is
478
479                  {x {n Term} {* {x {n AddOp} {n Term}}}}
480
481

BUGS, IDEAS, FEEDBACK

483       This document, and the package it describes, will  undoubtedly  contain
484       bugs  and other problems.  Please report such in the category pt of the
485       Tcllib Trackers  [http://core.tcl.tk/tcllib/reportlist].   Please  also
486       report  any  ideas  for  enhancements  you  may have for either package
487       and/or documentation.
488
489       When proposing code changes, please provide unified diffs, i.e the out‐
490       put of diff -u.
491
492       Note  further  that  attachments  are  strongly  preferred over inlined
493       patches. Attachments can be made by going  to  the  Edit  form  of  the
494       ticket  immediately  after  its  creation, and then using the left-most
495       button in the secondary navigation bar.
496

KEYWORDS

498       EBNF, JSON, LL(k), PEG, TDPL, context-free languages,  conversion,  ex‐
499       pression, format conversion, grammar, matching, parser, parsing expres‐
500       sion, parsing expression grammar, push down  automaton,  recursive  de‐
501       scent, serialization, state, top-down parsing languages, transducer
502

CATEGORY

504       Parsing and Grammars
505
507       Copyright (c) 2009 Andreas Kupries <andreas_kupries@users.sourceforge.net>
508
509
510
511
512tcllib                                 1                pt::peg::from::json(n)
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