1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
# -*- coding: utf-8 -*-
##############################################################################
# Name: peg_peg.py
# Purpose: PEG parser definition using PEG itself.
# Author: Igor R. Dejanovic <igor DOT dejanovic AT gmail DOT com>
# Copyright: (c) 2009 Igor R. Dejanovic <igor DOT dejanovic AT gmail DOT com>
# License: MIT License
#
# PEG can be used to describe PEG.
# This example demonstrates building PEG parser using PEG based grammar of PEG
# grammar definition language.
##############################################################################
from arpeggio import *
from arpeggio.export import PMDOTExporter, PTDOTExporter
from arpeggio.peg import ParserPEG
# Semantic actions
from arpeggio.peg import SemGrammar, SemRule, SemOrderedChoice, SemSequence,\
SemPrefix, SemSufix, SemExpression, SemRegEx, SemIdentifier, SemLiteral,\
SemTerminal
sem_actions = {
"grammar": SemGrammar(),
"rule": SemRule(),
"ordered_choice": SemOrderedChoice(),
"sequence": SemSequence(),
"prefix": SemPrefix(),
"sufix": SemSufix(),
"expression": SemExpression(),
"regex": SemRegEx(),
"identifier": SemIdentifier(),
"literal": SemLiteral()
}
for sem in ["LEFT_ARROW", "SLASH", "STAR", "QUESTION", "PLUS", "AND", "NOT",
"OPEN", "CLOSE"]:
sem_actions[sem] = SemTerminal()
# PEG defined using PEG itself.
peg_grammar = r"""
grammar <- rule+ EndOfFile;
rule <- identifier LEFT_ARROW ordered_choice ';';
ordered_choice <- sequence (SLASH sequence)*;
sequence <- prefix+;
prefix <- (AND/NOT)? sufix;
sufix <- expression (QUESTION/STAR/PLUS)?;
expression <- regex / (identifier !LEFT_ARROW)
/ ("(" ordered_choice ")") / literal;
identifier <- r'[a-zA-Z_]([a-zA-Z_]|[0-9])*';
regex <- 'r' '\'' r'(\\\'|[^\'])*' '\'';
literal <- r'\'(\\\'|[^\'])*\'|"[^"]*"';
LEFT_ARROW <- '<-';
SLASH <- '/';
AND <- '&';
NOT <- '!';
QUESTION <- '?';
STAR <- '*';
PLUS <- '+';
OPEN <- '(';
CLOSE <- ')';
DOT <- '.';
comment <- '//' r'.*\n';
"""
try:
# ParserPEG will use ParserPython to parse peg_grammar definition and
# create parser_model for parsing PEG based grammars
parser = ParserPEG(peg_grammar, 'grammar', debug=True)
# Exporting parser model to dot file for visualization.
PMDOTExporter().exportFile(parser.parser_model,
"peg_peg_parser_model.dot")
# Now we will use created parser to parse the same peg_grammar used for
# parser initialization. We can parse peg_grammar because it is specified
# using PEG itself.
parser.parse(peg_grammar)
# Again we export parse tree in dot file for vizualization.
PTDOTExporter().exportFile(parser.parse_tree,
"peg_peg_parse_tree.dot")
# ASG should be the same as parser.parser_model because semantic
# actions will create PEG parser (tree of ParsingExpressions).
asg = parser.getASG(sem_actions)
# This graph should be the same as peg_peg_parser_model.dot because
# they define the same parser.
PMDOTExporter().exportFile(asg,
"peg_peg_asg.dot")
# If we replace parser_mode with ASG constructed parser it will still
# parse PEG grammars
parser.parser_model = asg
parser.parse(peg_grammar)
except NoMatch, e:
print "Expected %s at position %s." % \
(e.value, str(e.parser.pos_to_linecol(e.position)))