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318
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1 #!/usr/bin/python
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2
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3 """ Parser generator utility """
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4
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5 import argparse
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6 import re
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7 import sys
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8 import datetime
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9 from pyyacc import Grammar, print_grammar
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10
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11
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12 class XaccLexer:
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13 def __init__(self):
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14 pass
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15
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16 def feed(self, txt):
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17 # Create a regular expression for the lexing part:
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18 tok_spec = [
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19 ('ID', r'[A-Za-z][A-Za-z\d_]*'),
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20 ('STRING', r"'[^']*'"),
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21 ('BRACEDCODE', r"\{[^\}]*\}"),
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22 ('OTHER', r'[:;\|]'),
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23 ('SKIP', r'[ ]')
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24 ]
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25 tok_re = '|'.join('(?P<%s>%s)' % pair for pair in tok_spec)
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26 gettok = re.compile(tok_re).match
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27
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28 lines = txt.split('\n')
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29
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30 def tokenize_line(line):
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31 """ Generator that splits up a line into tokens """
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32 mo = gettok(line)
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33 pos = 0
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34 while mo:
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35 typ = mo.lastgroup
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36 val = mo.group(typ)
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37 if typ == 'ID':
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38 yield (typ, val)
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39 elif typ == 'STRING':
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40 typ = 'ID'
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41 yield (typ, val[1:-1])
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42 elif typ == 'OTHER':
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43 typ = val
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44 yield (typ, val)
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45 elif typ == 'BRACEDCODE':
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46 yield (typ, val)
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47 elif typ == 'SKIP':
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48 pass
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49 else:
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50 raise NotImplementedError(str(typ))
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51 pos = mo.end()
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52 mo = gettok(line, pos)
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53 if len(line) != pos:
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54 raise ParseError('Lex fault at {}'.format(line))
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55
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56 def tokenize():
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57 section = 0
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58 for line in lines:
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59 line = line.strip()
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60 if not line:
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61 continue # Skip empty lines
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62 if line == '%%':
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63 section += 1
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64 yield('%%', '%%')
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65 continue
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66 if section == 0:
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67 if line.startswith('%tokens'):
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68 yield('%tokens', '%tokens')
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69 yield from tokenize_line(line[7:])
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70 else:
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71 yield ('HEADER', line)
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72 elif section == 1:
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73 yield from tokenize_line(line)
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74 yield ('eof', 'eof')
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75 self.tokens = tokenize()
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76 self.token = self.tokens.__next__()
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77
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78 def next_token(self):
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79 t = self.token
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80 if t[0] != 'eof':
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81 self.token = self.tokens.__next__()
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82 #print(t)
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83 return t
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84
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85
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86 class ParseError(Exception):
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87 pass
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88
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89
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90 class XaccParser:
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91 """ Implements a recursive descent parser to parse grammar rules.
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92 We could have made an generated parser, but that would yield a chicken
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93 egg issue.
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94 """
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95 def __init__(self, lexer):
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96 self.lexer = lexer
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97
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98 @property
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99 def Peak(self):
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100 """ Sneak peak to the next token in line """
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101 return self.lexer.token[0]
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102
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103 def next_token(self):
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104 """ Take the next token """
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105 return self.lexer.next_token()
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106
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107 def consume(self, typ):
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108 """ Eat next token of type typ or raise an exception """
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109 if self.Peak == typ:
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110 return self.next_token()
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111 else:
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112 raise ParseError('Expected {}, but got {}'.format(typ, self.Peak))
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113
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114 def has_consumed(self, typ):
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115 """ Consume typ if possible and return true if so """
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116 if self.Peak == typ:
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117 self.consume(typ)
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118 return True
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119 return False
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120
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121 def parse_grammar(self):
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122 """ Entry parse function into recursive descent parser """
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123 # parse header
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124 headers = []
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125 terminals = []
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126 while self.Peak in ['HEADER', '%tokens']:
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127 if self.Peak == '%tokens':
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128 self.consume('%tokens')
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129 while self.Peak == 'ID':
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130 terminals.append(self.consume('ID')[1])
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131 else:
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132 headers.append(self.consume('HEADER')[1])
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133 self.consume('%%')
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134 self.grammar = Grammar(terminals)
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135 while self.Peak != 'eof':
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136 self.parse_rule()
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137 return self.grammar
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138
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139 def parse_symbol(self):
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140 return self.consume('ID')[1]
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141
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142 def parse_rhs(self):
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143 symbols = []
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144 while self.Peak not in [';', 'BRACEDCODE', '|']:
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145 symbols.append(self.parse_symbol())
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146 if self.Peak == 'BRACEDCODE':
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147 action = self.consume('BRACEDCODE')[1]
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148 action = action[1:-1].strip()
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149 else:
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150 action = None
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151 return symbols, action
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152
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153 def parse_rule(self):
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154 p = self.parse_symbol()
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155 self.consume(':')
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156 symbols, action = self.parse_rhs()
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157 self.grammar.add_production(p, symbols, action)
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158 while self.has_consumed('|'):
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159 symbols, action = self.parse_rhs()
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160 self.grammar.add_production(p, symbols, action)
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161 self.consume(';')
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162
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163
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164 class XaccGenerator:
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165 """ Generator that writes generated parser to file """
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166 def __init__(self):
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167 pass
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168
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169 def generate(self, grammar, output_file):
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170 print_grammar(grammar)
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171 self.grammar = grammar
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172 self.action_table, self.goto_table = grammar.doGenerate()
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173 self.generate_python_script(output_file)
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174
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175 def generate_python_script(self, f):
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176 """ Generate python script with the parser table """
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177 print('#!/usr/bin/python', file=f)
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178 stamp = datetime.datetime.now().ctime()
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179 print('""" Automatically generated by xacc on {} """'.format(stamp), file=f)
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180 print('from pyyacc import LRParser, Reduce, Shift, Accept, Production, Grammar', file=f)
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181 print('from ppci import Token', file=f)
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182 print(file=f)
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183 print('class Parser(LRParser):', file=f)
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184 print(' def __init__(self):', file=f)
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185 # Generate rules:
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186 print(' self.start_symbol = "{}"'.format(self.grammar.start_symbol), file=f)
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187 print(' self.grammar = Grammar({})'.format(self.grammar.terminals), file=f)
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188 for rule_number, rule in enumerate(self.grammar.productions):
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189 rule.f_name = 'action_{}_{}'.format(rule.name, rule_number)
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190 print(' self.grammar.add_production("{}", {}, self.{})'.format(rule.name, rule.symbols, rule.f_name), file=f)
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191 # Fill action table:
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192 print(' self.action_table = {}', file=f)
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193 for state in self.action_table:
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194 action = self.action_table[state]
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195 print(' self.action_table[{}] = {}'.format(state, action), file=f)
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196 print('', file=f)
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197
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198 # Fill goto table:
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199 print(' self.goto_table = {}', file=f)
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200 for gt in self.goto_table:
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201 to = self.goto_table[gt]
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202 print(' self.goto_table[{}] = {}'.format(gt, to), file=f)
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203 print('', file=f)
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204
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205 # Generate a function for each action:
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206 for rule in self.grammar.productions:
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207 M = len(rule.symbols)
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208 args = ', '.join('arg{}'.format(n + 1) for n in range(M))
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209 print(' def {}(self, {}):'.format(rule.f_name, args), file=f)
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210 if rule.f == None:
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211 semantics = 'pass'
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212 else:
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213 semantics = str(rule.f)
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214 if semantics.strip() == '':
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215 semantics = 'pass'
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216 for n in range(M):
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217 semantics = semantics.replace('${}'.format(n + 1), 'arg{}'.format(n + 1))
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218 print(' {}'.format(semantics), file=f)
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219 print('', file=f)
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220
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221
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222 def main():
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223 # Parse arguments:
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224 parser = argparse.ArgumentParser(description='xacc compiler compiler')
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225 parser.add_argument('source', type=argparse.FileType('r'), \
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226 help='the parser specification')
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227 parser.add_argument('-o', '--output', type=argparse.FileType('w'), \
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228 default=sys.stdout)
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229 args = parser.parse_args()
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230 src = args.source.read()
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231 args.source.close()
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232
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233 # Construction of generator parts:
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234 lexer = XaccLexer()
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235 parser = XaccParser(lexer)
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236 generator = XaccGenerator()
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237
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238 # Sequence source through the generator parts:
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239 lexer.feed(src)
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240 grammar = parser.parse_grammar()
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241 generator.generate(grammar, args.output)
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242 args.output.close()
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243
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244
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245 if __name__ == '__main__':
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246 main()
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