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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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45 from pyyacc import Grammar
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46 from baselex import BaseLexer
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47 from ppci import Token
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48
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49
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50 class XaccLexer(BaseLexer):
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51 def __init__(self):
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52 tok_spec = [
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53 ('ID', r'[A-Za-z][A-Za-z\d_]*', lambda typ, val: (typ, val)),
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54 ('STRING', r"'[^']*'", lambda typ, val: ('ID', val[1:-1])),
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55 ('BRACEDCODE', r"\{[^\}]*\}", lambda typ, val: (typ, val)),
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56 ('OTHER', r'[:;\|]', lambda typ, val: (val, val)),
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57 ('SKIP', r'[ ]', None)
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58 ]
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59 super().__init__(tok_spec)
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60
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61 def tokenize(self, txt):
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62 lines = txt.split('\n')
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63 section = 0
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64 for line in lines:
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65 line = line.strip()
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66 if not line:
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67 continue # Skip empty lines
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68 if line == '%%':
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69 section += 1
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70 yield Token('%%', '%%')
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71 continue
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72 if section == 0:
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73 if line.startswith('%tokens'):
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74 yield Token('%tokens', '%tokens')
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75 for tk in super().tokenize(line[7:]):
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76 yield tk
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77 else:
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78 yield Token('HEADER', line)
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79 elif section == 1:
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80 for tk in super().tokenize(line):
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81 yield tk
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82
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83
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84 class ParseError(Exception):
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85 pass
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86
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87
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88 class XaccParser:
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89 """ Implements a recursive descent parser to parse grammar rules.
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90 We could have made an generated parser, but that would yield a chicken
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91 egg issue.
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92 """
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93 def __init__(self):
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94 pass
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95
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96 def prepare_peak(self, lexer):
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97 self.lexer = lexer
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98 self.look_ahead = self.lexer.next_token()
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99
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100 @property
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101 def Peak(self):
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102 """ Sneak peak to the next token in line """
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103 return self.look_ahead.typ
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104
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105 def next_token(self):
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106 """ Take the next token """
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107 token = self.look_ahead
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108 self.look_ahead = self.lexer.next_token()
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109 return token
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110
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111 def consume(self, typ):
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112 """ Eat next token of type typ or raise an exception """
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113 if self.Peak == typ:
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114 return self.next_token()
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115 else:
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116 raise ParseError('Expected {}, but got {}'.format(typ, self.Peak))
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117
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118 def has_consumed(self, typ):
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119 """ Consume typ if possible and return true if so """
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120 if self.Peak == typ:
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121 self.consume(typ)
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122 return True
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123 return False
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124
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125 def parse_grammar(self, lexer):
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126 """ Entry parse function into recursive descent parser """
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127 self.prepare_peak(lexer)
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128 # parse header
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129 self.headers = []
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130 terminals = []
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131 while self.Peak in ['HEADER', '%tokens']:
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132 if self.Peak == '%tokens':
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133 self.consume('%tokens')
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134 while self.Peak == 'ID':
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135 terminals.append(self.consume('ID').val)
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136 else:
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137 self.headers.append(self.consume('HEADER').val)
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138 self.consume('%%')
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139 self.grammar = Grammar(terminals)
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140 while self.Peak != 'EOF':
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141 self.parse_rule()
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142 return self.grammar
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143
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144 def parse_symbol(self):
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145 return self.consume('ID').val
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146
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147 def parse_rhs(self):
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148 """ Parse the right hand side of a rule definition """
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149 symbols = []
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150 while self.Peak not in [';', 'BRACEDCODE', '|']:
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151 symbols.append(self.parse_symbol())
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152 if self.Peak == 'BRACEDCODE':
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153 action = self.consume('BRACEDCODE').val
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154 action = action[1:-1].strip()
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155 else:
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156 action = None
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157 return symbols, action
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158
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159 def parse_rule(self):
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160 """ Parse a rule definition """
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161 p = self.parse_symbol()
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162 self.consume(':')
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163 symbols, action = self.parse_rhs()
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164 self.grammar.add_production(p, symbols, action)
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165 while self.has_consumed('|'):
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166 symbols, action = self.parse_rhs()
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167 self.grammar.add_production(p, symbols, action)
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168 self.consume(';')
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169
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170
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171 class XaccGenerator:
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172 """ Generator that writes generated parser to file """
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173 def __init__(self):
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174 self.logger = logging.getLogger('yacc')
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175
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176 def generate(self, grammar, headers, output_file):
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177 self.output_file = output_file
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178 self.grammar = grammar
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179 self.headers = headers
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180 self.logger.info('Generating parser for grammar {}'.format(grammar))
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181 self.action_table, self.goto_table = grammar.generate_tables()
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182 self.generate_python_script()
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183
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184 def print(self, *args):
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185 """ Print helper function that prints to output file """
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186 print(*args, file=self.output_file)
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187
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188 def generate_python_script(self):
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189 """ Generate python script with the parser table """
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190 self.print('#!/usr/bin/python')
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191 stamp = datetime.datetime.now().ctime()
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192 self.print('""" Automatically generated by xacc on {} """'.format(stamp))
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193 self.print('from pyyacc import LRParser, Reduce, Shift, Accept, Production, Grammar')
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194 self.print('from ppci import Token')
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195 self.print('')
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196 for h in self.headers:
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197 print(h, file=output_file)
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198 self.print('')
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199 self.print('class Parser(LRParser):')
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200 self.print(' def __init__(self):')
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201 # Generate rules:
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202 self.print(' self.start_symbol = "{}"'.format(self.grammar.start_symbol))
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203 self.print(' self.grammar = Grammar({})'.format(self.grammar.terminals))
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204 for rule_number, rule in enumerate(self.grammar.productions):
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205 rule.f_name = 'action_{}_{}'.format(rule.name, rule_number)
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206 self.print(' self.grammar.add_production("{}", {}, self.{})'.format(rule.name, rule.symbols, rule.f_name))
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207 # Fill action table:
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208 self.print(' self.action_table = {}')
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209 for state in self.action_table:
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210 action = self.action_table[state]
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211 self.print(' self.action_table[{}] = {}'.format(state, action))
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212 self.print('')
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213
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214 # Fill goto table:
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215 self.print(' self.goto_table = {}')
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216 for state_number in self.goto_table:
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217 to = self.goto_table[state_number]
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218 self.print(' self.goto_table[{}] = {}'.format(state_number, to))
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219 self.print('')
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220
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221 # Generate a function for each action:
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222 for rule in self.grammar.productions:
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223 num_symbols = len(rule.symbols)
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224 args = ', '.join('arg{}'.format(n + 1) for n in range(num_symbols))
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225 self.print(' def {}(self, {}):'.format(rule.f_name, args))
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226 if rule.f == None:
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227 semantics = 'pass'
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228 else:
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229 semantics = str(rule.f)
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230 if semantics.strip() == '':
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231 semantics = 'pass'
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232 for n in range(num_symbols):
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233 semantics = semantics.replace('${}'.format(n + 1), 'arg{}'.format(n + 1))
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234 self.print(' {}'.format(semantics))
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235 self.print('')
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236
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237
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238 def make_argument_parser():
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239 # Parse arguments:
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240 parser = argparse.ArgumentParser(description='xacc compiler compiler')
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241 parser.add_argument('source', type=argparse.FileType('r'), \
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242 help='the parser specification')
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243 parser.add_argument('-o', '--output', type=argparse.FileType('w'), \
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244 default=sys.stdout)
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245 return parser
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246
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247
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248 def load_as_module(filename):
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249 """ Load a parser spec file, generate LR tables and create module """
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250 ob = io.StringIO()
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251 args = argparse.Namespace(source=open(filename), output=ob)
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252 main(args)
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253
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254 parser_mod = types.ModuleType('generated_parser')
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255 exec(ob.getvalue(), parser_mod.__dict__)
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256 return parser_mod
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257
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258
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259 def main(args):
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260 src = args.source.read()
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261 args.source.close()
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262
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263 # Construction of generator parts:
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264 lexer = XaccLexer()
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265 parser = XaccParser()
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266 generator = XaccGenerator()
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267
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268 # Sequence source through the generator parts:
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269 lexer.feed(src)
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270 grammar = parser.parse_grammar(lexer)
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271 generator.generate(grammar, parser.headers, args.output)
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272
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273
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274 if __name__ == '__main__':
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275 args = make_argument_parser().parse_args()
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276 main(args)
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