annotate python/pyyacc.py @ 327:61c9df5bffce

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author Windel Bouwman
date Sat, 01 Feb 2014 17:21:21 +0100
parents 8d07a4254f04
children c7cc54c0dfdf
rev   line source
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1 """
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2 Parser generator script
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3 """
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4
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5 from ppci import Token
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6
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7 EPS = 'EPS'
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8 EOF = 'EOF'
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9
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10
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11 class ParserGenerationException(Exception):
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12 """ Raised when something goes wrong during parser generation """
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13 pass
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14
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15
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16 class ParserException(Exception):
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17 """ Raised during a failure in the parsing process """
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18 pass
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19
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20
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21 class Action:
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22 def __repr__(self):
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23 return 'Action'
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24
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25 def __eq__(self, other):
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26 return str(self) == str(other)
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27
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28
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29 class Shift(Action):
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30 def __init__(self, to_state):
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31 self.to_state = to_state
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32
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33 def __repr__(self):
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34 return 'Shift({})'.format(self.to_state)
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35
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36
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37 class Reduce(Action):
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38 def __init__(self, rule):
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39 self.rule = rule
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40
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41 def __repr__(self):
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42 return 'Reduce({})'.format(self.rule)
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43
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44
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45 class Accept(Reduce):
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46 def __repr__(self):
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47 return 'Accept({})'.format(self.rule)
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48
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49
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50 def print_grammar(g):
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51 """ Pretty print a grammar """
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52 print(g)
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53 for production in g.productions:
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54 print(production)
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55
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56
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57 def calculate_first_sets(grammar):
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58 """
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59 Calculate first sets for each grammar symbol
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60 This is a dictionary which maps each grammar symbol
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61 to a set of terminals that can be encountered first
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62 when looking for the symbol.
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63 """
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64 first = {}
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65 nullable = {}
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66 for terminal in grammar.terminals | {EOF, EPS}:
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67 first[terminal] = set([terminal])
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68 nullable[terminal] = False
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69 for nt in grammar.nonterminals:
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70 first[nt] = set()
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71 nullable[nt] = False
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72 while True:
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73 some_change = False
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74 for rule in grammar.productions:
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75 # Check for null-ability:
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76 if all(nullable[beta] for beta in rule.symbols):
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77 if not nullable[rule.name]:
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78 nullable[rule.name] = True
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79 some_change = True
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80 # Update first sets:
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81 for beta in rule.symbols:
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82 if not nullable[beta]:
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83 if first[beta] - first[rule.name]:
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84 first[rule.name] |= first[beta]
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85 some_change = True
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86 break
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87 if not some_change:
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88 break
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89 return first
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90
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91
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92 class Grammar:
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93 """ Defines a grammar of a language """
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94 def __init__(self, terminals):
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95 self.terminals = set(terminals)
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96 self.nonterminals = set()
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97 self.productions = []
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98 self._first = None # Cached first set
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99 self.start_symbol = None
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100
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101 def __repr__(self):
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102 return 'Grammar with {} rules'.format(len(self.productions))
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103
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104 def add_production(self, name, symbols, f=None):
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105 """ Add a production rule to the grammar """
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106 production = Production(name, symbols, f)
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107 self.productions.append(production)
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108 if name in self.terminals:
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109 raise ParserGenerationException("Cannot redefine terminal {0}".format(name))
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110 self.nonterminals.add(name)
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111 self._first = None # Invalidate cached version
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112
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113 def productionsForName(self, name):
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114 """ Retrieve all productions for a non terminal """
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115 return [p for p in self.productions if p.name == name]
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116
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117 @property
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118 def Symbols(self):
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119 """ Get all the symbols defined by this grammar """
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120 return self.nonterminals | self.terminals
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121
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122 @property
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123 def first(self):
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124 """
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125 The first set is a mapping from a grammar symbol to a set of
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126 set of all terminal symbols that can be the first terminal when
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127 looking for the grammar symbol
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128 """
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129 if not self._first:
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130 self._first = calculate_first_sets(self)
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131 return self._first
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132
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133 def closure(self, itemset):
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134 """ Expand itemset by using epsilon moves """
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135 worklist = list(itemset)
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136 def addIt(itm):
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137 if not itm in itemset:
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138 itemset.add(itm)
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139 worklist.append(itm)
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140 def first2(itm):
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141 # When using the first sets, create a copy:
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142 f = set(self.first[itm.NextNext])
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143 if EPS in f:
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144 f.discard(EPS)
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145 f.add(itm.look_ahead)
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146 return f
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147 # Start of algorithm:
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148 while worklist:
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149 item = worklist.pop(0)
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150 if not item.IsShift:
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151 continue
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152 if not (item.Next in self.nonterminals):
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153 continue
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154 C = item.Next
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155 for add_p in self.productionsForName(C):
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156 for b in first2(item):
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157 addIt(Item(add_p, 0, b))
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158 return frozenset(itemset)
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159
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160 def initialItemSet(self):
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161 """ Calculates the initial item set """
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162 iis = set()
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163 for p in self.productionsForName(self.start_symbol):
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164 iis.add(Item(p, 0, EOF))
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165 return self.closure(iis)
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166
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167 def nextItemSet(self, itemset, symbol):
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168 """
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169 Determines the next itemset for the current set and a symbol
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170 This is the goto procedure
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171 """
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172 next_set = set()
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173 for item in itemset:
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174 if item.can_shift_over(symbol):
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175 next_set.add(item.shifted())
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176 return self.closure(next_set)
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177
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178 def genCanonicalSet(self, iis):
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179 states = []
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180 worklist = []
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181 transitions = {}
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182 def addSt(s):
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183 if not (s in states):
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184 worklist.append(s)
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185 states.append(s)
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186 addSt(iis)
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187 while len(worklist) > 0:
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188 itemset = worklist.pop(0)
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parents: 181
diff changeset
189 for symbol in self.Symbols:
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190 nis = self.nextItemSet(itemset, symbol)
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parents: 181
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191 if not nis:
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192 continue
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parents: 181
diff changeset
193 addSt(nis)
185
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194 transitions[(states.index(itemset), symbol)] = states.index(nis)
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195 return states, transitions
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196
192
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197 def checkSymbols(self):
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198 """ Checks no symbols are undefined """
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199 for production in self.productions:
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diff changeset
200 for symbol in production.symbols:
319
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201 if symbol not in self.Symbols:
192
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202 raise ParserGenerationException('Symbol {0} undefined'.format(symbol))
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203
184
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parents: 181
diff changeset
204 def genParser(self):
218
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parents: 195
diff changeset
205 """ Generates a parser from the grammar (using a caching algorithm) """
240
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206 action_table, goto_table = self.doGenerate()
218
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207 p = LRParser(action_table, goto_table, self.start_symbol)
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208 p.grammar = self
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209 return p
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210
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211 def doGenerate(self):
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212 if not self.start_symbol:
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213 self.start_symbol = self.productions[0].name
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214 self.checkSymbols()
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215 action_table = {}
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216 goto_table = {}
184
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217 iis = self.initialItemSet()
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218
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219 # First generate all item sets by using the nextItemset function:
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220 states, transitions = self.genCanonicalSet(iis)
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221
185
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222 def setAction(state, t, action):
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223 assert isinstance(action, Action)
185
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224 key = (state, t)
218
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225 assert type(state) is int
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226 assert type(t) is str
185
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227 if key in action_table:
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228 action2 = action_table[key]
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229 if action != action2:
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230 if (type(action2) is Reduce) and (type(action) is Shift):
194
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231 # Automatically resolve and do the shift action!
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232 # Simple, but almost always what you want!!
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233 action_table[key] = action
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234 elif isinstance(action2, Shift) and isinstance(action, Reduce):
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235 pass
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236 else:
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237 a1 = str(action)
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238 a2 = str(action2)
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239 raise ParserGenerationException('LR construction conflict {0} vs {1}'.format(a1, a2))
185
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240 else:
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241 action_table[key] = action
184
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242
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243 # Fill action table:
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244 for state in states:
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245 # Detect conflicts:
184
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246 for item in state:
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247 if item.IsShift and item.Next in self.terminals:
185
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248 # Rule 1, a shift item:
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249 nextstate = transitions[(states.index(state), item.Next)]
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250 setAction(states.index(state), item.Next, Shift(nextstate))
185
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251 if item.IsReduce:
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252 if item.production.name == self.start_symbol and item.look_ahead == EOF:
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diff changeset
253 # Rule 3: accept:
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diff changeset
254 act = Accept(self.productions.index(item.production))
184
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parents: 181
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255 else:
185
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diff changeset
256 # Rule 2, reduce item:
318
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diff changeset
257 act = Reduce(self.productions.index(item.production))
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diff changeset
258 setAction(states.index(state), item.look_ahead, act)
185
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parents: 184
diff changeset
259 for nt in self.nonterminals:
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260 key = (states.index(state), nt)
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261 if key in transitions:
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diff changeset
262 goto_table[key] = transitions[key]
218
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diff changeset
263 return action_table, goto_table
185
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parents: 184
diff changeset
264
178
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parents:
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265
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parents:
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266 class Production:
181
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parents: 180
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267 """ Production rule for a grammar """
194
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268 def __init__(self, name, symbols, f=None):
181
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269 self.name = name
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270 self.symbols = symbols
194
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diff changeset
271 self.f = f
181
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parents: 180
diff changeset
272
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diff changeset
273 def __repr__(self):
318
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diff changeset
274 action = ' ' + str(self.f) if self.f else ''
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diff changeset
275 return '{0} -> {1}'.format(self.name, self.symbols) + action
181
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parents: 180
diff changeset
276
179
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diff changeset
277
178
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parents:
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278 class Item:
318
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diff changeset
279 """
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280 Represents a partially parsed item
186
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diff changeset
281 It has a production it is looking for, a position
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diff changeset
282 in this production called the 'dot' and a look ahead
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diff changeset
283 symbol that must follow this item.
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diff changeset
284 """
181
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parents: 180
diff changeset
285 def __init__(self, production, dotpos, look_ahead):
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diff changeset
286 self.production = production
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parents: 180
diff changeset
287 self.dotpos = dotpos
184
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parents: 181
diff changeset
288 assert self.dotpos <= len(self.production.symbols)
181
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diff changeset
289 self.look_ahead = look_ahead
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parents: 180
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290
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parents: 180
diff changeset
291 def getdata(self):
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parents: 180
diff changeset
292 """ Gets the members as a tuple """
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parents: 180
diff changeset
293 return (self.production, self.dotpos, self.look_ahead)
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parents: 180
diff changeset
294
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parents: 180
diff changeset
295 def __eq__(self, other):
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parents: 180
diff changeset
296 if type(other) is type(self):
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parents: 180
diff changeset
297 return self.getdata() == other.getdata()
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diff changeset
298 return False
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parents: 180
diff changeset
299
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parents: 180
diff changeset
300 def __hash__(self):
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parents: 180
diff changeset
301 return self.getdata().__hash__()
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parents: 180
diff changeset
302
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parents: 180
diff changeset
303 @property
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parents: 180
diff changeset
304 def IsReduce(self):
186
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parents: 185
diff changeset
305 """ Check if this item has the dot at the end """
181
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parents: 180
diff changeset
306 return self.dotpos == len(self.production.symbols)
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parents: 180
diff changeset
307
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parents: 180
diff changeset
308 @property
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diff changeset
309 def IsShift(self):
186
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parents: 185
diff changeset
310 """ Check if this item is a shift item, i.e. the dot can proceed """
181
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parents: 180
diff changeset
311 return not self.IsReduce
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diff changeset
312
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parents: 180
diff changeset
313 @property
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parents: 180
diff changeset
314 def Next(self):
186
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parents: 185
diff changeset
315 """ Returns the symbol after the dot """
181
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parents: 180
diff changeset
316 return self.production.symbols[self.dotpos]
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parents: 180
diff changeset
317
184
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parents: 181
diff changeset
318 def can_shift_over(self, symbol):
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parents: 181
diff changeset
319 """ Determines if this item can shift over the given symbol """
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parents: 181
diff changeset
320 return self.IsShift and self.Next == symbol
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parents: 181
diff changeset
321
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parents: 181
diff changeset
322 def shifted(self):
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parents: 181
diff changeset
323 """ Creates a new item that is shifted one position """
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parents: 181
diff changeset
324 return Item(self.production, self.dotpos + 1, self.look_ahead)
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parents: 181
diff changeset
325
181
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parents: 180
diff changeset
326 @property
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parents: 180
diff changeset
327 def NextNext(self):
186
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parents: 185
diff changeset
328 """ Gets the symbol after the next symbol, or EPS if at the end """
181
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parents: 180
diff changeset
329 if self.dotpos + 1 >= len(self.production.symbols):
184
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parents: 181
diff changeset
330 return EPS
181
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parents: 180
diff changeset
331 else:
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parents: 180
diff changeset
332 return self.production.symbols[self.dotpos + 1]
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parents: 180
diff changeset
333
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parents: 180
diff changeset
334 def __repr__(self):
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parents: 180
diff changeset
335 prod = self.production
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parents: 180
diff changeset
336 predot = ' '.join(prod.symbols[0:self.dotpos])
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parents: 180
diff changeset
337 postdot = ' '.join(prod.symbols[self.dotpos:])
186
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parents: 185
diff changeset
338 name = prod.name
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parents: 185
diff changeset
339 args = (name, predot, postdot, self.look_ahead)
185
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parents: 184
diff changeset
340 return '[{0} -> {1} . {2} -> {3}]'.format(*args)
181
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parents: 180
diff changeset
341
179
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parents: 178
diff changeset
342
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parents: 178
diff changeset
343 class LRParser:
318
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diff changeset
344 """ LR parser automata """
195
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parents: 194
diff changeset
345 def __init__(self, action_table, goto_table, start_symbol):
184
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parents: 181
diff changeset
346 self.action_table = action_table
185
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parents: 184
diff changeset
347 self.goto_table = goto_table
195
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parents: 194
diff changeset
348 self.start_symbol = start_symbol
184
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parents: 181
diff changeset
349
318
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parents: 240
diff changeset
350 def parse(self, lexer):
191
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parents: 186
diff changeset
351 """ Parse an iterable with tokens """
318
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parents: 240
diff changeset
352 assert hasattr(lexer, 'next_token'), '{0} is no lexer'.format(type(lexer))
185
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parents: 184
diff changeset
353 stack = [0]
195
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parents: 194
diff changeset
354 r_data_stack = []
318
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parents: 240
diff changeset
355 look_ahead = lexer.next_token()
191
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parents: 186
diff changeset
356 assert type(look_ahead) is Token
195
37ac6c016e0f Expanded asm subsystem
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parents: 194
diff changeset
357 # TODO: exit on this condition:
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parents: 194
diff changeset
358 while stack != [0, self.start_symbol, 2222]:
181
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parents: 180
diff changeset
359 state = stack[-1] # top of stack
191
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parents: 186
diff changeset
360 key = (state, look_ahead.typ)
181
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parents: 180
diff changeset
361 if not key in self.action_table:
194
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parents: 192
diff changeset
362 raise ParserException('Error parsing at character {0}'.format(look_ahead))
318
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parents: 240
diff changeset
363 action = self.action_table[key]
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parents: 240
diff changeset
364 if type(action) is Reduce:
194
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parents: 192
diff changeset
365 f_args = []
318
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366 prod = self.grammar.productions[action.rule]
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367 for s in prod.symbols:
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368 stack.pop()
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369 stack.pop()
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370 f_args.append(r_data_stack.pop())
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371 f_args.reverse()
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372 r_data = None
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373 if prod.f:
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374 r_data = prod.f(*f_args)
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375 state = stack[-1]
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376 stack.append(prod.name)
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377 stack.append(self.goto_table[(state, prod.name)])
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378 r_data_stack.append(r_data)
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379 elif type(action) is Shift:
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380 stack.append(look_ahead.typ)
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381 stack.append(action.to_state)
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382 r_data_stack.append(look_ahead)
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383 look_ahead = lexer.next_token()
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384 assert type(look_ahead) is Token
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385 elif type(action) is Accept:
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386 # Pop last rule data off the stack:
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387 f_args = []
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388 param = self.grammar.productions[action.rule]
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389 for s in param.symbols:
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390 stack.pop()
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391 stack.pop()
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392 f_args.append(r_data_stack.pop())
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393 f_args.reverse()
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394 if param.f:
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395 ret_val = param.f(*f_args)
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396 else:
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397 ret_val = None
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398 # Break out!
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399 break
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400 # At exit, the stack must be 1 long
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401 # TODO: fix that this holds:
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402 #assert len(stack) == 1, 'stack {0} not totally reduce'.format(stack)
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403 return ret_val