1pt_parse_peg(i) Parser Tools pt_parse_peg(i)
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6
8 pt_parse_peg - Parser Tools PEG Parser
9
11 package require Tcl 8.5
12 package require pt::parse::peg 1
14 pt::parse::peg ?objectName?
16 objectName destroy
18 objectName parse chan
20 objectName parset text
22______________________________________________________________________________
24
26 Are you lost ? Do you have trouble understanding this document ? In
27 that case please read the overview provided by the Introduction to
28 Parser Tools. This document is the entrypoint to the whole system the
29 current package is a part of.
30 This package provides a class whose instances are parsers for parsing
32 expression grammars in textual form.
33
35 pt::parse::peg ?objectName?
36 The class command constructs parser instances, i.e. objects. The
37 result of the command is the fully-qualified name of the
38 instance command.
39 If no objectName is specified the class will generate and use an
41 automatic name. If the objectName was specified, but is not
42 fully qualified the command will be created in the current
43 namespace.
44
46 All parser instances provide at least the methods shown below:
47 objectName destroy
49 This method destroys the parser instance, releasing all claimed
50 memory and other resources, and deleting the instance command.
51 The result of the command is the empty string.
53 objectName parse chan
55 This method runs the parser using the contents of chan as input
56 (starting at the current location in the channel), until parsing
57 is not possible anymore, either because parsing has completed,
58 or run into a syntax error.
59 Note here that the Parser Tools are based on Tcl 8.5+. In other
61 words, the channel argument is not restricted to files, sockets,
62 etc. We have the full power of reflected channels available.
63 It should also be noted that the parser pulls the characters
65 from the input stream as it needs them. If a parser created by
66 this package has to be operated in a push aka event-driven man‐
67 ner it will be necessary to go to Tcl 8.6+ and use the corou‐
68 tine::auto to wrap it into a coroutine where read is properly
69 changed for push-operation.
70 Upon successful completion the command returns an abstract syn‐
72 tax tree as its result. This AST is in the form specified in
73 section AST serialization format. As a plain nested Tcl-list it
74 can then be processed with any Tcl commands the user likes,
75 doing transformations, semantic checks, etc. To help in this
76 the package pt::ast provides a set of convenience commands for
77 validation of the tree's basic structure, printing it for debug‐
78 ging, and walking it either from the bottom up, or top down.
79 When encountering a syntax error the command will throw an error
81 instead. This error will be a 4-element Tcl-list, containing,
82 in the order listed below:
83 [1] The string pt::rde identifying it as parser runtime
85 error.
86 [2] The location of the parse error, as character offset from
88 the beginning of the parsed input.
89 [3] The location of parse error, now as a 2-element list con‐
91 taining line-number and column in the line.
92 [4] A set of atomic parsing expressions indicating encoding
94 the characters and/or nonterminal symbols the parser
95 expected to see at the location of the parse error, but
96 did not get. For the specification of atomic parsing
97 expressions please see the section PE serialization for‐
98 mat.
99 objectName parset text
101 This method runs the parser using the string in text as input.
102 In all other ways it behaves like the method parse, shown above.
103
105 This document, and the package it describes, will undoubtedly contain
106 bugs and other problems. Please report such in the category pt of the
107 Tcllib Trackers [http://core.tcl.tk/tcllib/reportlist]. Please also
108 report any ideas for enhancements you may have for either package
109 and/or documentation.
110 When proposing code changes, please provide unified diffs, i.e the out‐
112 put of diff -u.
113 Note further that attachments are strongly preferred over inlined
115 patches. Attachments can be made by going to the Edit form of the
116 ticket immediately after its creation, and then using the left-most
117 button in the secondary navigation bar.
118
120 EBNF, LL(k), PEG, TDPL, context-free languages, expression, grammar,
121 matching, parser, parsing expression, parsing expression grammar, push
122 down automaton, recursive descent, state, top-down parsing languages,
123 transducer
124
126 Parsing and Grammars
127
129 Copyright (c) 2009 Andreas Kupries <andreas_kupries@users.sourceforge.net>
130tcllib 1 pt_parse_peg(i)