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1 #!/usr/bin/python
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2
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3 """
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4 Parser generator utility. This script can generate a python script from a
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5 grammar description.
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6
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7 Invoke the script on a grammar specification file:
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8
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9 .. code::
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10
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11 $ ./yacc.py test.x -o test_parser.py
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12
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13 And use the generated parser by deriving a user class:
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14
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15
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16 .. code::
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17
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18 import test_parser
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19 class MyParser(test_parser.Parser):
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20 pass
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21 p = MyParser()
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22 p.parse()
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23
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24
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25 Alternatively you can load the parser on the fly:
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26
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27 .. code::
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28
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29 import yacc
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30 parser_mod = yacc.load_as_module('mygrammar.x')
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31 class MyParser(parser_mod.Parser):
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32 pass
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33 p = MyParser()
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34 p.parse()
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35
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36 """
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37
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38 import argparse
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39 import re
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40 import sys
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41 import datetime
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42 import types
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43 import io
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44 import logging
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334
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45 from pyyacc import Grammar
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46
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47
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48 class XaccLexer:
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49 def __init__(self):
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50 pass
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51
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52 def feed(self, txt):
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53 # Create a regular expression for the lexing part:
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54 tok_spec = [
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55 ('ID', r'[A-Za-z][A-Za-z\d_]*'),
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56 ('STRING', r"'[^']*'"),
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57 ('BRACEDCODE', r"\{[^\}]*\}"),
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58 ('OTHER', r'[:;\|]'),
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59 ('SKIP', r'[ ]')
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60 ]
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61 tok_re = '|'.join('(?P<%s>%s)' % pair for pair in tok_spec)
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62 gettok = re.compile(tok_re).match
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63
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64 lines = txt.split('\n')
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65
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66 def tokenize_line(line):
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67 """ Generator that splits up a line into tokens """
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68 mo = gettok(line)
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69 pos = 0
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70 while mo:
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71 typ = mo.lastgroup
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72 val = mo.group(typ)
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73 if typ == 'ID':
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74 yield (typ, val)
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75 elif typ == 'STRING':
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76 typ = 'ID'
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77 yield (typ, val[1:-1])
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78 elif typ == 'OTHER':
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79 typ = val
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80 yield (typ, val)
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81 elif typ == 'BRACEDCODE':
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82 yield (typ, val)
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83 elif typ == 'SKIP':
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84 pass
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85 else:
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86 raise NotImplementedError(str(typ))
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87 pos = mo.end()
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88 mo = gettok(line, pos)
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89 if len(line) != pos:
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90 raise ParseError('Lex fault at {}'.format(line))
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91
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92 def tokenize():
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93 section = 0
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94 for line in lines:
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95 line = line.strip()
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96 if not line:
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97 continue # Skip empty lines
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98 if line == '%%':
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99 section += 1
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100 yield('%%', '%%')
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101 continue
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102 if section == 0:
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103 if line.startswith('%tokens'):
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104 yield('%tokens', '%tokens')
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105 yield from tokenize_line(line[7:])
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106 else:
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107 yield ('HEADER', line)
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108 elif section == 1:
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109 yield from tokenize_line(line)
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110 yield ('eof', 'eof')
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111 self.tokens = tokenize()
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112 self.token = self.tokens.__next__()
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113
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114 def next_token(self):
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115 t = self.token
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116 if t[0] != 'eof':
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117 self.token = self.tokens.__next__()
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118 return t
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119
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120
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121 class ParseError(Exception):
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122 pass
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123
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124
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125 class XaccParser:
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126 """ Implements a recursive descent parser to parse grammar rules.
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127 We could have made an generated parser, but that would yield a chicken
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128 egg issue.
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129 """
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130 def __init__(self, lexer):
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131 self.lexer = lexer
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132
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133 @property
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134 def Peak(self):
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135 """ Sneak peak to the next token in line """
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136 return self.lexer.token[0]
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137
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138 def next_token(self):
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139 """ Take the next token """
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140 return self.lexer.next_token()
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141
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142 def consume(self, typ):
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143 """ Eat next token of type typ or raise an exception """
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144 if self.Peak == typ:
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145 return self.next_token()
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146 else:
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147 raise ParseError('Expected {}, but got {}'.format(typ, self.Peak))
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148
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149 def has_consumed(self, typ):
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150 """ Consume typ if possible and return true if so """
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151 if self.Peak == typ:
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152 self.consume(typ)
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153 return True
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154 return False
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155
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156 def parse_grammar(self):
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157 """ Entry parse function into recursive descent parser """
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158 # parse header
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159 headers = []
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160 terminals = []
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161 while self.Peak in ['HEADER', '%tokens']:
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162 if self.Peak == '%tokens':
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163 self.consume('%tokens')
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164 while self.Peak == 'ID':
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165 terminals.append(self.consume('ID')[1])
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166 else:
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167 headers.append(self.consume('HEADER')[1])
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168 self.consume('%%')
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169 self.headers = headers
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170 self.grammar = Grammar(terminals)
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171 while self.Peak != 'eof':
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172 self.parse_rule()
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173 return self.grammar
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174
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175 def parse_symbol(self):
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176 return self.consume('ID')[1]
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177
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178 def parse_rhs(self):
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179 """ Parse the right hand side of a rule definition """
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180 symbols = []
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181 while self.Peak not in [';', 'BRACEDCODE', '|']:
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182 symbols.append(self.parse_symbol())
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183 if self.Peak == 'BRACEDCODE':
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184 action = self.consume('BRACEDCODE')[1]
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185 action = action[1:-1].strip()
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186 else:
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187 action = None
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188 return symbols, action
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189
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190 def parse_rule(self):
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319
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191 """ Parse a rule definition """
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192 p = self.parse_symbol()
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193 self.consume(':')
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194 symbols, action = self.parse_rhs()
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195 self.grammar.add_production(p, symbols, action)
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196 while self.has_consumed('|'):
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197 symbols, action = self.parse_rhs()
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198 self.grammar.add_production(p, symbols, action)
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199 self.consume(';')
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200
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201
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202 class XaccGenerator:
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203 """ Generator that writes generated parser to file """
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204 def __init__(self):
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205 self.logger = logging.getLogger('yacc')
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206
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207 def generate(self, grammar, headers, output_file):
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208 self.output_file = output_file
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209 self.grammar = grammar
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210 self.headers = headers
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211 self.logger.info('Generating parser for grammar {}'.format(grammar))
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212 self.action_table, self.goto_table = grammar.generate_tables()
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213 self.generate_python_script()
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214
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215 def print(self, *args):
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216 """ Print helper function that prints to output file """
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217 print(*args, file=self.output_file)
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218
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219 def generate_python_script(self):
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220 """ Generate python script with the parser table """
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221 self.print('#!/usr/bin/python')
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222 stamp = datetime.datetime.now().ctime()
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223 self.print('""" Automatically generated by xacc on {} """'.format(stamp))
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224 self.print('from pyyacc import LRParser, Reduce, Shift, Accept, Production, Grammar')
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225 self.print('from ppci import Token')
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226 self.print('')
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227 for h in self.headers:
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228 print(h, file=output_file)
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229 self.print('')
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230 self.print('class Parser(LRParser):')
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231 self.print(' def __init__(self):')
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232 # Generate rules:
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233 self.print(' self.start_symbol = "{}"'.format(self.grammar.start_symbol))
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234 self.print(' self.grammar = Grammar({})'.format(self.grammar.terminals))
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235 for rule_number, rule in enumerate(self.grammar.productions):
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236 rule.f_name = 'action_{}_{}'.format(rule.name, rule_number)
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237 self.print(' self.grammar.add_production("{}", {}, self.{})'.format(rule.name, rule.symbols, rule.f_name))
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238 # Fill action table:
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239 self.print(' self.action_table = {}')
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240 for state in self.action_table:
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241 action = self.action_table[state]
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242 self.print(' self.action_table[{}] = {}'.format(state, action))
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243 self.print('')
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244
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245 # Fill goto table:
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246 self.print(' self.goto_table = {}')
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247 for state_number in self.goto_table:
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248 to = self.goto_table[state_number]
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249 self.print(' self.goto_table[{}] = {}'.format(state_number, to))
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250 self.print('')
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251
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252 # Generate a function for each action:
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253 for rule in self.grammar.productions:
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254 num_symbols = len(rule.symbols)
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255 args = ', '.join('arg{}'.format(n + 1) for n in range(num_symbols))
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256 self.print(' def {}(self, {}):'.format(rule.f_name, args))
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257 if rule.f == None:
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258 semantics = 'pass'
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259 else:
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260 semantics = str(rule.f)
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261 if semantics.strip() == '':
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262 semantics = 'pass'
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263 for n in range(num_symbols):
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264 semantics = semantics.replace('${}'.format(n + 1), 'arg{}'.format(n + 1))
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265 self.print(' {}'.format(semantics))
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266 self.print('')
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267
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268
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269 def make_argument_parser():
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270 # Parse arguments:
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271 parser = argparse.ArgumentParser(description='xacc compiler compiler')
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272 parser.add_argument('source', type=argparse.FileType('r'), \
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273 help='the parser specification')
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274 parser.add_argument('-o', '--output', type=argparse.FileType('w'), \
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275 default=sys.stdout)
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276 return parser
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277
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278
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279 def load_as_module(filename):
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280 """ Load a parser spec file, generate LR tables and create module """
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281 ob = io.StringIO()
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282 args = argparse.Namespace(source=open(filename), output=ob)
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283 main(args)
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284
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285 parser_mod = types.ModuleType('generated_parser')
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286 exec(ob.getvalue(), parser_mod.__dict__)
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287 return parser_mod
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288
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290 def main(args):
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291 src = args.source.read()
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292 args.source.close()
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293
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294 # Construction of generator parts:
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295 lexer = XaccLexer()
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296 parser = XaccParser(lexer)
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297 generator = XaccGenerator()
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298
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299 # Sequence source through the generator parts:
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300 lexer.feed(src)
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301 grammar = parser.parse_grammar()
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302 generator.generate(grammar, parser.headers, args.output)
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303
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304
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305 if __name__ == '__main__':
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306 args = make_argument_parser().parse_args()
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307 main(args)
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