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3<title>PLY Internals</title>
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7<h1>PLY Internals</h1>
8 
9<b>
10David M. Beazley <br>
11dave@dabeaz.com<br>
12</b>
13
14<p>
15<b>PLY Version: 3.0</b>
16<p>
17
18<!-- INDEX -->
19<div class="sectiontoc">
20<ul>
21<li><a href="#internal_nn1">Introduction</a>
22<li><a href="#internal_nn2">Grammar Class</a>
23<li><a href="#internal_nn3">Productions</a>
24<li><a href="#internal_nn4">LRItems</a>
25<li><a href="#internal_nn5">LRTable</a>
26<li><a href="#internal_nn6">LRGeneratedTable</a>
27<li><a href="#internal_nn7">LRParser</a>
28<li><a href="#internal_nn8">ParserReflect</a>
29<li><a href="#internal_nn9">High-level operation</a>
30</ul>
31</div>
32<!-- INDEX -->
33
34
35<H2><a name="internal_nn1"></a>1. Introduction</H2>
36
37
38This document describes classes and functions that make up the internal
39operation of PLY.  Using this programming interface, it is possible to
40manually build an parser using a different interface specification
41than what PLY normally uses.  For example, you could build a gramar
42from information parsed in a completely different input format.  Some of
43these objects may be useful for building more advanced parsing engines
44such as GLR.
45
46<p>
47It should be stressed that using PLY at this level is not for the
48faint of heart.  Generally, it's assumed that you know a bit of
49the underlying compiler theory and how an LR parser is put together.
50
51<H2><a name="internal_nn2"></a>2. Grammar Class</H2>
52
53
54The file <tt>ply.yacc</tt> defines a class <tt>Grammar</tt> that 
55is used to hold and manipulate information about a grammar
56specification.   It encapsulates the same basic information
57about a grammar that is put into a YACC file including 
58the list of tokens, precedence rules, and grammar rules. 
59Various operations are provided to perform different validations
60on the grammar.  In addition, there are operations to compute
61the first and follow sets that are needed by the various table
62generation algorithms.
63
64<p>
65<tt><b>Grammar(terminals)</b></tt>
66
67<blockquote>
68Creates a new grammar object.  <tt>terminals</tt> is a list of strings
69specifying the terminals for the grammar.  An instance <tt>g</tt> of
70<tt>Grammar</tt> has the following methods:
71</blockquote>
72
73<p>
74<b><tt>g.set_precedence(term,assoc,level)</tt></b>
75<blockquote>
76Sets the precedence level and associativity for a given terminal <tt>term</tt>.  
77<tt>assoc</tt> is one of <tt>'right'</tt>,
78<tt>'left'</tt>, or <tt>'nonassoc'</tt> and <tt>level</tt> is a positive integer.  The higher
79the value of <tt>level</tt>, the higher the precedence.  Here is an example of typical
80precedence settings:
81
82<pre>
83g.set_precedence('PLUS',  'left',1)
84g.set_precedence('MINUS', 'left',1)
85g.set_precedence('TIMES', 'left',2)
86g.set_precedence('DIVIDE','left',2)
87g.set_precedence('UMINUS','left',3)
88</pre>
89
90This method must be called prior to adding any productions to the
91grammar with <tt>g.add_production()</tt>.  The precedence of individual grammar
92rules is determined by the precedence of the right-most terminal.
93
94</blockquote>
95<p>
96<b><tt>g.add_production(name,syms,func=None,file='',line=0)</tt></b>
97<blockquote>
98Adds a new grammar rule.  <tt>name</tt> is the name of the rule,
99<tt>syms</tt> is a list of symbols making up the right hand
100side of the rule, <tt>func</tt> is the function to call when
101reducing the rule.   <tt>file</tt> and <tt>line</tt> specify
102the filename and line number of the rule and are used for
103generating error messages.    
104
105<p>
106The list of symbols in <tt>syms</tt> may include character
107literals and <tt>%prec</tt> specifiers.  Here are some
108examples:
109
110<pre>
111g.add_production('expr',['expr','PLUS','term'],func,file,line)
112g.add_production('expr',['expr','"+"','term'],func,file,line)
113g.add_production('expr',['MINUS','expr','%prec','UMINUS'],func,file,line)
114</pre>
115
116<p>
117If any kind of error is detected, a <tt>GrammarError</tt> exception
118is raised with a message indicating the reason for the failure.
119</blockquote>
120
121<p>
122<b><tt>g.set_start(start=None)</tt></b>
123<blockquote>
124Sets the starting rule for the grammar.  <tt>start</tt> is a string
125specifying the name of the start rule.   If <tt>start</tt> is omitted,
126the first grammar rule added with <tt>add_production()</tt> is taken to be
127the starting rule.  This method must always be called after all
128productions have been added.
129</blockquote>
130
131<p>
132<b><tt>g.find_unreachable()</tt></b>
133<blockquote>
134Diagnostic function.  Returns a list of all unreachable non-terminals
135defined in the grammar.  This is used to identify inactive parts of
136the grammar specification.
137</blockquote>
138
139<p>
140<b><tt>g.infinite_cycle()</tt></b>
141<blockquote>
142Diagnostic function.  Returns a list of all non-terminals in the
143grammar that result in an infinite cycle.  This condition occurs if
144there is no way for a grammar rule to expand to a string containing
145only terminal symbols.
146</blockquote>
147
148<p>
149<b><tt>g.undefined_symbols()</tt></b>
150<blockquote>
151Diagnostic function.  Returns a list of tuples <tt>(name, prod)</tt>
152corresponding to undefined symbols in the grammar. <tt>name</tt> is the
153name of the undefined symbol and <tt>prod</tt> is an instance of 
154<tt>Production</tt> which has information about the production rule
155where the undefined symbol was used.
156</blockquote>
157
158<p>
159<b><tt>g.unused_terminals()</tt></b>
160<blockquote>
161Diagnostic function.  Returns a list of terminals that were defined,
162but never used in the grammar.
163</blockquote>
164
165<p>
166<b><tt>g.unused_rules()</tt></b>
167<blockquote>
168Diagnostic function.  Returns a list of <tt>Production</tt> instances
169corresponding to production rules that were defined in the grammar,
170but never used anywhere.  This is slightly different
171than <tt>find_unreachable()</tt>.
172</blockquote>
173
174<p>
175<b><tt>g.unused_precedence()</tt></b>
176<blockquote>
177Diagnostic function.  Returns a list of tuples <tt>(term, assoc)</tt> 
178corresponding to precedence rules that were set, but never used the
179grammar.  <tt>term</tt> is the terminal name and <tt>assoc</tt> is the
180precedence associativity (e.g., <tt>'left'</tt>, <tt>'right'</tt>, 
181or <tt>'nonassoc'</tt>.
182</blockquote>
183
184<p>
185<b><tt>g.compute_first()</tt></b>
186<blockquote>
187Compute all of the first sets for all symbols in the grammar.  Returns a dictionary
188mapping symbol names to a list of all first symbols.
189</blockquote>
190
191<p>
192<b><tt>g.compute_follow()</tt></b>
193<blockquote>
194Compute all of the follow sets for all non-terminals in the grammar.
195The follow set is the set of all possible symbols that might follow a
196given non-terminal.  Returns a dictionary mapping non-terminal names
197to a list of symbols.
198</blockquote>
199
200<p>
201<b><tt>g.build_lritems()</tt></b>
202<blockquote>
203Calculates all of the LR items for all productions in the grammar.  This
204step is required before using the grammar for any kind of table generation.
205See the section on LR items below.
206</blockquote>
207
208<p>
209The following attributes are set by the above methods and may be useful
210in code that works with the grammar.  All of these attributes should be
211assumed to be read-only.  Changing their values directly will likely 
212break the grammar.
213
214<p>
215<b><tt>g.Productions</tt></b>
216<blockquote>
217A list of all productions added.  The first entry is reserved for
218a production representing the starting rule.  The objects in this list
219are instances of the <tt>Production</tt> class, described shortly.
220</blockquote>
221
222<p>
223<b><tt>g.Prodnames</tt></b>
224<blockquote>
225A dictionary mapping the names of nonterminals to a list of all
226productions of that nonterminal.
227</blockquote>
228
229<p>
230<b><tt>g.Terminals</tt></b>
231<blockquote>
232A dictionary mapping the names of terminals to a list of the
233production numbers where they are used.
234</blockquote>
235
236<p>
237<b><tt>g.Nonterminals</tt></b>
238<blockquote>
239A dictionary mapping the names of nonterminals to a list of the
240production numbers where they are used.
241</blockquote>
242
243<p>
244<b><tt>g.First</tt></b>
245<blockquote>
246A dictionary representing the first sets for all grammar symbols.  This is
247computed and returned by the <tt>compute_first()</tt> method.
248</blockquote>
249
250<p>
251<b><tt>g.Follow</tt></b>
252<blockquote>
253A dictionary representing the follow sets for all grammar rules.  This is
254computed and returned by the <tt>compute_follow()</tt> method.
255</blockquote>
256
257<p>
258<b><tt>g.Start</tt></b>
259<blockquote>
260Starting symbol for the grammar.  Set by the <tt>set_start()</tt> method.
261</blockquote>
262
263For the purposes of debugging, a <tt>Grammar</tt> object supports the <tt>__len__()</tt> and
264<tt>__getitem__()</tt> special methods.  Accessing <tt>g[n]</tt> returns the nth production
265from the grammar.
266
267
268<H2><a name="internal_nn3"></a>3. Productions</H2>
269
270
271<tt>Grammar</tt> objects store grammar rules as instances of a <tt>Production</tt> class.  This
272class has no public constructor--you should only create productions by calling <tt>Grammar.add_production()</tt>.
273The following attributes are available on a <tt>Production</tt> instance <tt>p</tt>.
274
275<p>
276<b><tt>p.name</tt></b>
277<blockquote>
278The name of the production. For a grammar rule such as <tt>A : B C D</tt>, this is <tt>'A'</tt>.
279</blockquote>
280
281<p>
282<b><tt>p.prod</tt></b>
283<blockquote>
284A tuple of symbols making up the right-hand side of the production.  For a grammar rule such as <tt>A : B C D</tt>, this is <tt>('B','C','D')</tt>.
285</blockquote>
286
287<p>
288<b><tt>p.number</tt></b>
289<blockquote>
290Production number.  An integer containing the index of the production in the grammar's <tt>Productions</tt> list.
291</blockquote>
292
293<p>
294<b><tt>p.func</tt></b>
295<blockquote>
296The name of the reduction function associated with the production.
297This is the function that will execute when reducing the entire
298grammar rule during parsing.
299</blockquote>
300
301<p>
302<b><tt>p.callable</tt></b>
303<blockquote>
304The callable object associated with the name in <tt>p.func</tt>.  This is <tt>None</tt>
305unless the production has been bound using <tt>bind()</tt>.
306</blockquote>
307
308<p>
309<b><tt>p.file</tt></b>
310<blockquote>
311Filename associated with the production.  Typically this is the file where the production was defined.  Used for error messages.
312</blockquote>
313
314<p>
315<b><tt>p.lineno</tt></b>
316<blockquote>
317Line number associated with the production.  Typically this is the line number in <tt>p.file</tt> where the production was defined.  Used for error messages.
318</blockquote>
319
320<p>
321<b><tt>p.prec</tt></b>
322<blockquote>
323Precedence and associativity associated with the production.  This is a tuple <tt>(assoc,level)</tt> where
324<tt>assoc</tt> is one of <tt>'left'</tt>,<tt>'right'</tt>, or <tt>'nonassoc'</tt> and <tt>level</tt> is
325an integer.   This value is determined by the precedence of the right-most terminal symbol in the production
326or by use of the <tt>%prec</tt> specifier when adding the production.
327</blockquote>
328
329<p>
330<b><tt>p.usyms</tt></b>
331<blockquote>
332A list of all unique symbols found in the production.
333</blockquote>
334
335<p>
336<b><tt>p.lr_items</tt></b>
337<blockquote>
338A list of all LR items for this production.  This attribute only has a meaningful value if the
339<tt>Grammar.build_lritems()</tt> method has been called.  The items in this list are 
340instances of <tt>LRItem</tt> described below.
341</blockquote>
342
343<p>
344<b><tt>p.lr_next</tt></b>
345<blockquote>
346The head of a linked-list representation of the LR items in <tt>p.lr_items</tt>.  
347This attribute only has a meaningful value if the <tt>Grammar.build_lritems()</tt> 
348method has been called.  Each <tt>LRItem</tt> instance has a <tt>lr_next</tt> attribute
349to move to the next item.  The list is terminated by <tt>None</tt>.
350</blockquote>
351
352<p>
353<b><tt>p.bind(dict)</tt></b>
354<blockquote>
355Binds the production function name in <tt>p.func</tt> to a callable object in 
356<tt>dict</tt>.   This operation is typically carried out in the last step
357prior to running the parsing engine and is needed since parsing tables are typically
358read from files which only include the function names, not the functions themselves.
359</blockquote>
360
361<P>
362<tt>Production</tt> objects support
363the <tt>__len__()</tt>, <tt>__getitem__()</tt>, and <tt>__str__()</tt>
364special methods.
365<tt>len(p)</tt> returns the number of symbols in <tt>p.prod</tt>
366and <tt>p[n]</tt> is the same as <tt>p.prod[n]</tt>. 
367
368<H2><a name="internal_nn4"></a>4. LRItems</H2>
369
370
371The construction of parsing tables in an LR-based parser generator is primarily
372done over a set of "LR Items".   An LR item represents a stage of parsing one
373of the grammar rules.   To compute the LR items, it is first necessary to
374call <tt>Grammar.build_lritems()</tt>.  Once this step, all of the productions
375in the grammar will have their LR items attached to them.
376
377<p>
378Here is an interactive example that shows what LR items look like if you
379interactively experiment.  In this example, <tt>g</tt> is a <tt>Grammar</tt> 
380object.
381
382<blockquote>
383<pre>
384>>> <b>g.build_lritems()</b>
385>>> <b>p = g[1]</b>
386>>> <b>p</b>
387Production(statement -> ID = expr)
388>>>
389</pre>
390</blockquote>
391
392In the above code, <tt>p</tt> represents the first grammar rule. In
393this case, a rule <tt>'statement -> ID = expr'</tt>.
394
395<p>
396Now, let's look at the LR items for <tt>p</tt>.
397
398<blockquote>
399<pre>
400>>> <b>p.lr_items</b>
401[LRItem(statement -> . ID = expr), 
402 LRItem(statement -> ID . = expr), 
403 LRItem(statement -> ID = . expr), 
404 LRItem(statement -> ID = expr .)]
405>>>
406</pre>
407</blockquote>
408
409In each LR item, the dot (.) represents a specific stage of parsing.  In each LR item, the dot
410is advanced by one symbol.  It is only when the dot reaches the very end that a production
411is successfully parsed.
412
413<p>
414An instance <tt>lr</tt> of <tt>LRItem</tt> has the following
415attributes that hold information related to that specific stage of
416parsing.
417
418<p>
419<b><tt>lr.name</tt></b>
420<blockquote>
421The name of the grammar rule. For example, <tt>'statement'</tt> in the above example.
422</blockquote>
423
424<p>
425<b><tt>lr.prod</tt></b>
426<blockquote>
427A tuple of symbols representing the right-hand side of the production, including the
428special <tt>'.'</tt> character.  For example, <tt>('ID','.','=','expr')</tt>.
429</blockquote>
430
431<p>
432<b><tt>lr.number</tt></b>
433<blockquote>
434An integer representing the production number in the grammar.
435</blockquote>
436
437<p>
438<b><tt>lr.usyms</tt></b>
439<blockquote>
440A set of unique symbols in the production.  Inherited from the original <tt>Production</tt> instance.
441</blockquote>
442
443<p>
444<b><tt>lr.lr_index</tt></b>
445<blockquote>
446An integer representing the position of the dot (.).  You should never use <tt>lr.prod.index()</tt>
447to search for it--the result will be wrong if the grammar happens to also use (.) as a character
448literal.
449</blockquote>
450
451<p>
452<b><tt>lr.lr_after</tt></b>
453<blockquote>
454A list of all productions that can legally appear immediately to the right of the
455dot (.).  This list contains <tt>Production</tt> instances.   This attribute
456represents all of the possible branches a parse can take from the current position.
457For example, suppose that <tt>lr</tt> represents a stage immediately before
458an expression like this:
459
460<pre>
461>>> <b>lr</b>
462LRItem(statement -> ID = . expr)
463>>>
464</pre>
465
466Then, the value of <tt>lr.lr_after</tt> might look like this, showing all productions that
467can legally appear next:
468
469<pre>
470>>> <b>lr.lr_after</b>
471[Production(expr -> expr PLUS expr), 
472 Production(expr -> expr MINUS expr), 
473 Production(expr -> expr TIMES expr), 
474 Production(expr -> expr DIVIDE expr), 
475 Production(expr -> MINUS expr), 
476 Production(expr -> LPAREN expr RPAREN), 
477 Production(expr -> NUMBER), 
478 Production(expr -> ID)]
479>>>
480</pre>
481
482</blockquote>
483
484<p>
485<b><tt>lr.lr_before</tt></b>
486<blockquote>
487The grammar symbol that appears immediately before the dot (.) or <tt>None</tt> if
488at the beginning of the parse.  
489</blockquote>
490
491<p>
492<b><tt>lr.lr_next</tt></b>
493<blockquote>
494A link to the next LR item, representing the next stage of the parse.  <tt>None</tt> if <tt>lr</tt>
495is the last LR item.
496</blockquote>
497
498<tt>LRItem</tt> instances also support the <tt>__len__()</tt> and <tt>__getitem__()</tt> special methods.
499<tt>len(lr)</tt> returns the number of items in <tt>lr.prod</tt> including the dot (.). <tt>lr[n]</tt>
500returns <tt>lr.prod[n]</tt>.
501
502<p>
503It goes without saying that all of the attributes associated with LR
504items should be assumed to be read-only.  Modifications will very
505likely create a small black-hole that will consume you and your code.
506
507<H2><a name="internal_nn5"></a>5. LRTable</H2>
508
509
510The <tt>LRTable</tt> class is used to represent LR parsing table data. This
511minimally includes the production list, action table, and goto table. 
512
513<p>
514<b><tt>LRTable()</tt></b>
515<blockquote>
516Create an empty LRTable object.  This object contains only the information needed to
517run an LR parser.  
518</blockquote>
519
520An instance <tt>lrtab</tt> of <tt>LRTable</tt> has the following methods:
521
522<p>
523<b><tt>lrtab.read_table(module)</tt></b>
524<blockquote>
525Populates the LR table with information from the module specified in <tt>module</tt>.
526<tt>module</tt> is either a module object already loaded with <tt>import</tt> or
527the name of a Python module.   If it's a string containing a module name, it is
528loaded and parsing data is extracted.   Returns the signature  value that was used
529when initially writing the tables.  Raises a <tt>VersionError</tt> exception if
530the module was created using an incompatible version of PLY.
531</blockquote>
532
533<p>
534<b><tt>lrtab.bind_callables(dict)</tt></b>
535<blockquote>
536This binds all of the function names used in productions to callable objects
537found in the dictionary <tt>dict</tt>.  During table generation and when reading
538LR tables from files, PLY only uses the names of action functions such as <tt>'p_expr'</tt>,
539<tt>'p_statement'</tt>, etc.  In order to actually run the parser, these names
540have to be bound to callable objects.   This method is always called prior to
541running a parser.
542</blockquote>
543
544After <tt>lrtab</tt> has been populated, the following attributes are defined.
545
546<p>
547<b><tt>lrtab.lr_method</tt></b>
548<blockquote>
549The LR parsing method used (e.g., <tt>'LALR'</tt>)
550</blockquote>
551
552
553<p>
554<b><tt>lrtab.lr_productions</tt></b>
555<blockquote>
556The production list.  If the parsing tables have been newly
557constructed, this will be a list of <tt>Production</tt> instances.  If
558the parsing tables have been read from a file, it's a list
559of <tt>MiniProduction</tt> instances.  This, together
560with <tt>lr_action</tt> and <tt>lr_goto</tt> contain all of the
561information needed by the LR parsing engine.
562</blockquote>
563
564<p>
565<b><tt>lrtab.lr_action</tt></b>
566<blockquote>
567The LR action dictionary that implements the underlying state machine.
568The keys of this dictionary are the LR states.
569</blockquote>
570
571<p>
572<b><tt>lrtab.lr_goto</tt></b>
573<blockquote>
574The LR goto table that contains information about grammar rule reductions.
575</blockquote>
576
577
578<H2><a name="internal_nn6"></a>6. LRGeneratedTable</H2>
579
580
581The <tt>LRGeneratedTable</tt> class represents constructed LR parsing tables on a
582grammar.  It is a subclass of <tt>LRTable</tt>.
583
584<p>
585<b><tt>LRGeneratedTable(grammar, method='LALR',log=None)</tt></b>
586<blockquote>
587Create the LR parsing tables on a grammar.  <tt>grammar</tt> is an instance of <tt>Grammar</tt>,
588<tt>method</tt> is a string with the parsing method (<tt>'SLR'</tt> or <tt>'LALR'</tt>), and
589<tt>log</tt> is a logger object used to write debugging information.  The debugging information
590written to <tt>log</tt> is the same as what appears in the <tt>parser.out</tt> file created
591by yacc.  By supplying a custom logger with a different message format, it is possible to get
592more information (e.g., the line number in <tt>yacc.py</tt> used for issuing each line of
593output in the log).   The result is an instance of <tt>LRGeneratedTable</tt>.
594</blockquote>
595
596<p>
597An instance <tt>lr</tt> of <tt>LRGeneratedTable</tt> has the following attributes.
598
599<p>
600<b><tt>lr.grammar</tt></b>
601<blockquote>
602A link to the Grammar object used to construct the parsing tables.
603</blockquote>
604
605<p>
606<b><tt>lr.lr_method</tt></b>
607<blockquote>
608The LR parsing method used (e.g., <tt>'LALR'</tt>)
609</blockquote>
610
611
612<p>
613<b><tt>lr.lr_productions</tt></b>
614<blockquote>
615A reference to <tt>grammar.Productions</tt>.  This, together with <tt>lr_action</tt> and <tt>lr_goto</tt>
616contain all of the information needed by the LR parsing engine.
617</blockquote>
618
619<p>
620<b><tt>lr.lr_action</tt></b>
621<blockquote>
622The LR action dictionary that implements the underlying state machine.  The keys of this dictionary are
623the LR states.
624</blockquote>
625
626<p>
627<b><tt>lr.lr_goto</tt></b>
628<blockquote>
629The LR goto table that contains information about grammar rule reductions.
630</blockquote>
631
632<p>
633<b><tt>lr.sr_conflicts</tt></b>
634<blockquote>
635A list of tuples <tt>(state,token,resolution)</tt> identifying all shift/reduce conflicts. <tt>state</tt> is the LR state
636number where the conflict occurred, <tt>token</tt> is the token causing the conflict, and <tt>resolution</tt> is
637a string describing the resolution taken.  <tt>resolution</tt> is either <tt>'shift'</tt> or <tt>'reduce'</tt>.
638</blockquote>
639
640<p>
641<b><tt>lr.rr_conflicts</tt></b>
642<blockquote>
643A list of tuples <tt>(state,rule,rejected)</tt> identifying all reduce/reduce conflicts.  <tt>state</tt> is the
644LR state number where the conflict occurred, <tt>rule</tt> is the production rule that was selected
645and <tt>rejected</tt> is the production rule that was rejected.   Both <tt>rule</tt> and </tt>rejected</tt> are
646instances of <tt>Production</tt>.  They can be inspected to provide the user with more information.
647</blockquote>
648
649<p>
650There are two public methods of <tt>LRGeneratedTable</tt>.
651
652<p>
653<b><tt>lr.write_table(modulename,outputdir="",signature="")</tt></b>
654<blockquote>
655Writes the LR parsing table information to a Python module.  <tt>modulename</tt> is a string 
656specifying the name of a module such as <tt>"parsetab"</tt>.  <tt>outputdir</tt> is the name of a 
657directory where the module should be created.  <tt>signature</tt> is a string representing a
658grammar signature that's written into the output file. This can be used to detect when
659the data stored in a module file is out-of-sync with the the grammar specification (and that
660the tables need to be regenerated).  If <tt>modulename</tt> is a string <tt>"parsetab"</tt>,
661this function creates a file called <tt>parsetab.py</tt>.  If the module name represents a
662package such as <tt>"foo.bar.parsetab"</tt>, then only the last component, <tt>"parsetab"</tt> is
663used.
664</blockquote>
665
666
667<H2><a name="internal_nn7"></a>7. LRParser</H2>
668
669
670The <tt>LRParser</tt> class implements the low-level LR parsing engine.
671
672
673<p>
674<b><tt>LRParser(lrtab, error_func)</tt></b>
675<blockquote>
676Create an LRParser.  <tt>lrtab</tt> is an instance of <tt>LRTable</tt>
677containing the LR production and state tables.  <tt>error_func</tt> is the
678error function to invoke in the event of a parsing error.
679</blockquote>
680
681An instance <tt>p</tt> of <tt>LRParser</tt> has the following methods:
682
683<p>
684<b><tt>p.parse(input=None,lexer=None,debug=0,tracking=0,tokenfunc=None)</tt></b>
685<blockquote>
686Run the parser.  <tt>input</tt> is a string, which if supplied is fed into the
687lexer using its <tt>input()</tt> method.  <tt>lexer</tt> is an instance of the
688<tt>Lexer</tt> class to use for tokenizing.  If not supplied, the last lexer
689created with the <tt>lex</tt> module is used.   <tt>debug</tt> is a boolean flag
690that enables debugging.   <tt>tracking</tt> is a boolean flag that tells the
691parser to perform additional line number tracking.  <tt>tokenfunc</tt> is a callable
692function that returns the next token.  If supplied, the parser will use it to get
693all tokens.
694</blockquote>
695
696<p>
697<b><tt>p.restart()</tt></b>
698<blockquote>
699Resets the parser state for a parse already in progress.
700</blockquote>
701
702<H2><a name="internal_nn8"></a>8. ParserReflect</H2>
703
704
705<p>
706The <tt>ParserReflect</tt> class is used to collect parser specification data
707from a Python module or object.   This class is what collects all of the
708<tt>p_rule()</tt> functions in a PLY file, performs basic error checking,
709and collects all of the needed information to build a grammar.    Most of the
710high-level PLY interface as used by the <tt>yacc()</tt> function is actually
711implemented by this class.
712
713<p>
714<b><tt>ParserReflect(pdict, log=None)</tt></b>
715<blockquote>
716Creates a <tt>ParserReflect</tt> instance. <tt>pdict</tt> is a dictionary
717containing parser specification data.  This dictionary typically corresponds
718to the module or class dictionary of code that implements a PLY parser.
719<tt>log</tt> is a logger instance that will be used to report error
720messages.
721</blockquote>
722
723An instance <tt>p</tt> of <tt>ParserReflect</tt> has the following methods:
724
725<p>
726<b><tt>p.get_all()</tt></b>
727<blockquote>
728Collect and store all required parsing information.
729</blockquote>
730
731<p>
732<b><tt>p.validate_all()</tt></b>
733<blockquote>
734Validate all of the collected parsing information.  This is a seprate step
735from <tt>p.get_all()</tt> as a performance optimization.  In order to
736increase parser start-up time, a parser can elect to only validate the
737parsing data when regenerating the parsing tables.   The validation
738step tries to collect as much information as possible rather than
739raising an exception at the first sign of trouble.  The attribute
740<tt>p.error</tt> is set if there are any validation errors.  The
741value of this attribute is also returned.
742</blockquote>
743
744<p>
745<b><tt>p.signature()</tt></b>
746<blockquote>
747Compute a signature representing the contents of the collected parsing
748data.  The signature value should change if anything in the parser
749specification has changed in a way that would justify parser table
750regeneration.   This method can be called after <tt>p.get_all()</tt>,
751but before <tt>p.validate_all()</tt>.
752</blockquote>
753
754The following attributes are set in the process of collecting data:
755
756<p>
757<b><tt>p.start</tt></b>
758<blockquote>
759The grammar start symbol, if any. Taken from <tt>pdict['start']</tt>.
760</blockquote>
761
762<p>
763<b><tt>p.error_func</tt></b>
764<blockquote>
765The error handling function or <tt>None</tt>. Taken from <tt>pdict['p_error']</tt>.
766</blockquote>
767
768<p>
769<b><tt>p.tokens</tt></b>
770<blockquote>
771The token list. Taken from <tt>pdict['tokens']</tt>.
772</blockquote>
773
774<p>
775<b><tt>p.prec</tt></b>
776<blockquote>
777The precedence specifier.  Taken from <tt>pdict['precedence']</tt>.
778</blockquote>
779
780<p>
781<b><tt>p.preclist</tt></b>
782<blockquote>
783A parsed version of the precedence specified.  A list of tuples of the form
784<tt>(token,assoc,level)</tt> where <tt>token</tt> is the terminal symbol,
785<tt>assoc</tt> is the associativity (e.g., <tt>'left'</tt>) and <tt>level</tt>
786is a numeric precedence level.
787</blockquote>
788
789<p>
790<b><tt>p.grammar</tt></b>
791<blockquote>
792A list of tuples <tt>(name, rules)</tt> representing the grammar rules. <tt>name</tt> is the
793name of a Python function or method in <tt>pdict</tt> that starts with <tt>"p_"</tt>.
794<tt>rules</tt> is a list of tuples <tt>(filename,line,prodname,syms)</tt> representing
795the grammar rules found in the documentation string of that function. <tt>filename</tt> and <tt>line</tt> contain location
796information that can be used for debugging. <tt>prodname</tt> is the name of the 
797production. <tt>syms</tt> is the right-hand side of the production.  If you have a
798function like this
799
800<pre>
801def p_expr(p):
802    '''expr : expr PLUS expr
803            | expr MINUS expr
804            | expr TIMES expr
805            | expr DIVIDE expr'''
806</pre>
807
808then the corresponding entry in <tt>p.grammar</tt> might look like this:
809
810<pre>
811('p_expr', [ ('calc.py',10,'expr', ['expr','PLUS','expr']),
812             ('calc.py',11,'expr', ['expr','MINUS','expr']),
813             ('calc.py',12,'expr', ['expr','TIMES','expr']),
814             ('calc.py',13,'expr', ['expr','DIVIDE','expr'])
815           ])
816</pre>
817</blockquote>
818
819<p>
820<b><tt>p.pfuncs</tt></b>
821<blockquote>
822A sorted list of tuples <tt>(line, file, name, doc)</tt> representing all of
823the <tt>p_</tt> functions found. <tt>line</tt> and <tt>file</tt> give location
824information.  <tt>name</tt> is the name of the function. <tt>doc</tt> is the
825documentation string.   This list is sorted in ascending order by line number.
826</blockquote>
827
828<p>
829<b><tt>p.files</tt></b>
830<blockquote>
831A dictionary holding all of the source filenames that were encountered
832while collecting parser information.  Only the keys of this dictionary have
833any meaning.
834</blockquote>
835
836<p>
837<b><tt>p.error</tt></b>
838<blockquote>
839An attribute that indicates whether or not any critical errors 
840occurred in validation.  If this is set, it means that that some kind
841of problem was detected and that no further processing should be
842performed.
843</blockquote>
844
845
846<H2><a name="internal_nn9"></a>9. High-level operation</H2>
847
848
849Using all of the above classes requires some attention to detail.  The <tt>yacc()</tt>
850function carries out a very specific sequence of operations to create a grammar.
851This same sequence should be emulated if you build an alternative PLY interface.
852
853<ol>
854<li>A <tt>ParserReflect</tt> object is created and raw grammar specification data is
855collected.
856<li>A <tt>Grammar</tt> object is created and populated with information
857from the specification data.
858<li>A <tt>LRGenerator</tt> object is created to run the LALR algorithm over
859the <tt>Grammar</tt> object.
860<li>Productions in the LRGenerator and bound to callables using the <tt>bind_callables()</tt>
861method.
862<li>A <tt>LRParser</tt> object is created from from the information in the
863<tt>LRGenerator</tt> object.
864</ol>
865
866</body>
867</html>
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