Mercurial > lcfOS
annotate python/pyyacc.py @ 357:818be710e13d
Added acceptance function to burg
| author | Windel Bouwman |
|---|---|
| date | Fri, 14 Mar 2014 15:14:29 +0100 |
| parents | 3bb7dcfe5529 |
| children | 9667d78ba79e |
| 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 |
| 191 | 5 from ppci import Token |
| 6 | |
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7 EPS = 'EPS' |
| 184 | 8 EOF = 'EOF' |
| 318 | 9 |
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10 |
| 185 | 11 class ParserGenerationException(Exception): |
| 186 | 12 """ Raised when something goes wrong during parser generation """ |
| 185 | 13 pass |
| 14 | |
| 15 | |
| 16 class ParserException(Exception): | |
| 186 | 17 """ Raised during a failure in the parsing process """ |
| 185 | 18 pass |
| 19 | |
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20 |
| 318 | 21 class Action: |
| 22 def __repr__(self): | |
| 23 return 'Action' | |
| 24 | |
| 25 def __eq__(self, other): | |
| 26 return str(self) == str(other) | |
| 27 | |
| 28 | |
| 29 class Shift(Action): | |
| 30 def __init__(self, to_state): | |
| 31 self.to_state = to_state | |
| 32 | |
| 33 def __repr__(self): | |
| 34 return 'Shift({})'.format(self.to_state) | |
| 35 | |
| 36 | |
| 37 class Reduce(Action): | |
| 38 def __init__(self, rule): | |
| 39 self.rule = rule | |
| 40 | |
| 41 def __repr__(self): | |
| 42 return 'Reduce({})'.format(self.rule) | |
| 43 | |
| 44 | |
| 45 class Accept(Reduce): | |
| 46 def __repr__(self): | |
| 47 return 'Accept({})'.format(self.rule) | |
| 48 | |
| 49 | |
| 50 def print_grammar(g): | |
| 51 """ Pretty print a grammar """ | |
| 52 print(g) | |
| 53 for production in g.productions: | |
| 54 print(production) | |
| 55 | |
| 319 | 56 |
| 57 def calculate_first_sets(grammar): | |
| 58 """ | |
| 59 Calculate first sets for each grammar symbol | |
| 60 This is a dictionary which maps each grammar symbol | |
| 61 to a set of terminals that can be encountered first | |
| 62 when looking for the symbol. | |
| 63 """ | |
| 64 first = {} | |
| 65 nullable = {} | |
| 66 for terminal in grammar.terminals | {EOF, EPS}: | |
| 67 first[terminal] = set([terminal]) | |
| 68 nullable[terminal] = False | |
| 69 for nt in grammar.nonterminals: | |
| 70 first[nt] = set() | |
| 71 nullable[nt] = False | |
| 72 while True: | |
| 73 some_change = False | |
| 74 for rule in grammar.productions: | |
| 75 # Check for null-ability: | |
| 76 if all(nullable[beta] for beta in rule.symbols): | |
| 77 if not nullable[rule.name]: | |
| 78 nullable[rule.name] = True | |
| 79 some_change = True | |
| 80 # Update first sets: | |
| 81 for beta in rule.symbols: | |
| 82 if not nullable[beta]: | |
| 83 if first[beta] - first[rule.name]: | |
| 84 first[rule.name] |= first[beta] | |
| 85 some_change = True | |
| 86 break | |
| 87 if not some_change: | |
| 88 break | |
| 89 return first | |
| 90 | |
| 91 | |
| 178 | 92 class Grammar: |
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93 """ Defines a grammar of a language """ |
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94 def __init__(self, terminals): |
| 319 | 95 self.terminals = set(terminals) |
| 96 self.nonterminals = set() | |
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97 self.productions = [] |
| 185 | 98 self._first = None # Cached first set |
| 318 | 99 self.start_symbol = None |
| 100 | |
| 101 def __repr__(self): | |
| 102 return 'Grammar with {} rules'.format(len(self.productions)) | |
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103 |
| 194 | 104 def add_production(self, name, symbols, f=None): |
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105 """ Add a production rule to the grammar """ |
| 194 | 106 production = Production(name, symbols, f) |
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107 self.productions.append(production) |
| 192 | 108 if name in self.terminals: |
| 109 raise ParserGenerationException("Cannot redefine terminal {0}".format(name)) | |
| 319 | 110 self.nonterminals.add(name) |
| 194 | 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 """ |
| 319 | 120 return self.nonterminals | self.terminals |
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121 |
| 185 | 122 @property |
| 123 def first(self): | |
| 318 | 124 """ |
| 186 | 125 The first set is a mapping from a grammar symbol to a set of |
| 126 set of all terminal symbols that can be the first terminal when | |
| 318 | 127 looking for the grammar symbol |
| 186 | 128 """ |
| 185 | 129 if not self._first: |
| 319 | 130 self._first = calculate_first_sets(self) |
| 185 | 131 return self._first |
| 132 | |
| 184 | 133 def closure(self, itemset): |
| 134 """ Expand itemset by using epsilon moves """ | |
| 135 worklist = list(itemset) | |
| 136 def addIt(itm): | |
| 137 if not itm in itemset: | |
| 138 itemset.add(itm) | |
| 139 worklist.append(itm) | |
| 186 | 140 def first2(itm): |
| 184 | 141 # When using the first sets, create a copy: |
| 186 | 142 f = set(self.first[itm.NextNext]) |
| 184 | 143 if EPS in f: |
| 144 f.discard(EPS) | |
| 186 | 145 f.add(itm.look_ahead) |
| 184 | 146 return f |
| 319 | 147 # Start of algorithm: |
| 184 | 148 while worklist: |
| 149 item = worklist.pop(0) | |
| 150 if not item.IsShift: | |
| 151 continue | |
| 152 if not (item.Next in self.nonterminals): | |
| 153 continue | |
| 154 C = item.Next | |
| 155 for add_p in self.productionsForName(C): | |
| 186 | 156 for b in first2(item): |
| 184 | 157 addIt(Item(add_p, 0, b)) |
| 158 return frozenset(itemset) | |
| 159 | |
| 160 def initialItemSet(self): | |
| 161 """ Calculates the initial item set """ | |
| 162 iis = set() | |
| 163 for p in self.productionsForName(self.start_symbol): | |
| 164 iis.add(Item(p, 0, EOF)) | |
| 165 return self.closure(iis) | |
| 166 | |
| 167 def nextItemSet(self, itemset, symbol): | |
| 318 | 168 """ |
| 319 | 169 Determines the next itemset for the current set and a symbol |
| 184 | 170 This is the goto procedure |
| 171 """ | |
| 172 next_set = set() | |
| 173 for item in itemset: | |
| 174 if item.can_shift_over(symbol): | |
| 175 next_set.add(item.shifted()) | |
| 176 return self.closure(next_set) | |
| 318 | 177 |
| 184 | 178 def genCanonicalSet(self, iis): |
| 185 | 179 states = [] |
| 184 | 180 worklist = [] |
| 185 | 181 transitions = {} |
| 184 | 182 def addSt(s): |
| 183 if not (s in states): | |
| 184 worklist.append(s) | |
| 185 | 185 states.append(s) |
| 184 | 186 addSt(iis) |
| 187 while len(worklist) > 0: | |
| 188 itemset = worklist.pop(0) | |
| 189 for symbol in self.Symbols: | |
| 190 nis = self.nextItemSet(itemset, symbol) | |
| 191 if not nis: | |
| 192 continue | |
| 193 addSt(nis) | |
| 185 | 194 transitions[(states.index(itemset), symbol)] = states.index(nis) |
| 195 return states, transitions | |
| 318 | 196 |
| 192 | 197 def checkSymbols(self): |
| 198 """ Checks no symbols are undefined """ | |
| 199 for production in self.productions: | |
| 200 for symbol in production.symbols: | |
| 319 | 201 if symbol not in self.Symbols: |
| 192 | 202 raise ParserGenerationException('Symbol {0} undefined'.format(symbol)) |
| 203 | |
| 340 | 204 def generate_parser(self): |
| 205 """ Generates a parser from the grammar """ | |
| 206 action_table, goto_table = self.generate_tables() | |
| 218 | 207 p = LRParser(action_table, goto_table, self.start_symbol) |
| 208 p.grammar = self | |
| 209 return p | |
| 210 | |
| 340 | 211 def generate_tables(self): |
| 212 """ Generate parsing tables """ | |
| 318 | 213 if not self.start_symbol: |
| 214 self.start_symbol = self.productions[0].name | |
| 192 | 215 self.checkSymbols() |
| 184 | 216 action_table = {} |
| 185 | 217 goto_table = {} |
| 184 | 218 iis = self.initialItemSet() |
| 219 | |
| 220 # First generate all item sets by using the nextItemset function: | |
| 185 | 221 states, transitions = self.genCanonicalSet(iis) |
| 194 | 222 |
| 185 | 223 def setAction(state, t, action): |
| 318 | 224 assert isinstance(action, Action) |
| 185 | 225 key = (state, t) |
| 218 | 226 assert type(state) is int |
| 227 assert type(t) is str | |
| 185 | 228 if key in action_table: |
| 229 action2 = action_table[key] | |
| 230 if action != action2: | |
| 318 | 231 if (type(action2) is Reduce) and (type(action) is Shift): |
| 194 | 232 # Automatically resolve and do the shift action! |
| 233 # Simple, but almost always what you want!! | |
| 234 action_table[key] = action | |
| 318 | 235 elif isinstance(action2, Shift) and isinstance(action, Reduce): |
| 236 pass | |
| 194 | 237 else: |
| 318 | 238 a1 = str(action) |
| 239 a2 = str(action2) | |
| 240 raise ParserGenerationException('LR construction conflict {0} vs {1}'.format(a1, a2)) | |
| 185 | 241 else: |
| 242 action_table[key] = action | |
| 184 | 243 |
| 244 # Fill action table: | |
| 245 for state in states: | |
| 185 | 246 # Detect conflicts: |
| 184 | 247 for item in state: |
| 248 if item.IsShift and item.Next in self.terminals: | |
| 185 | 249 # Rule 1, a shift item: |
| 250 nextstate = transitions[(states.index(state), item.Next)] | |
| 318 | 251 setAction(states.index(state), item.Next, Shift(nextstate)) |
| 185 | 252 if item.IsReduce: |
| 253 if item.production.name == self.start_symbol and item.look_ahead == EOF: | |
| 254 # Rule 3: accept: | |
| 318 | 255 act = Accept(self.productions.index(item.production)) |
| 184 | 256 else: |
| 185 | 257 # Rule 2, reduce item: |
| 318 | 258 act = Reduce(self.productions.index(item.production)) |
| 259 setAction(states.index(state), item.look_ahead, act) | |
| 185 | 260 for nt in self.nonterminals: |
| 261 key = (states.index(state), nt) | |
| 262 if key in transitions: | |
| 263 goto_table[key] = transitions[key] | |
| 218 | 264 return action_table, goto_table |
| 185 | 265 |
| 178 | 266 |
| 267 class Production: | |
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268 """ Production rule for a grammar """ |
| 341 | 269 def __init__(self, name, symbols, f): |
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270 self.name = name |
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271 self.symbols = symbols |
| 194 | 272 self.f = f |
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273 |
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274 def __repr__(self): |
| 318 | 275 action = ' ' + str(self.f) if self.f else '' |
| 276 return '{0} -> {1}'.format(self.name, self.symbols) + action | |
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277 |
| 179 | 278 |
| 178 | 279 class Item: |
| 318 | 280 """ |
| 281 Represents a partially parsed item | |
| 186 | 282 It has a production it is looking for, a position |
| 283 in this production called the 'dot' and a look ahead | |
| 284 symbol that must follow this item. | |
| 285 """ | |
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286 def __init__(self, production, dotpos, look_ahead): |
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287 self.production = production |
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288 self.dotpos = dotpos |
| 184 | 289 assert self.dotpos <= len(self.production.symbols) |
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290 self.look_ahead = look_ahead |
| 346 | 291 self._is_shift = self.dotpos < len(self.production.symbols) |
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292 |
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293 def getdata(self): |
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294 """ Gets the members as a tuple """ |
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295 return (self.production, self.dotpos, self.look_ahead) |
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296 |
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297 def __eq__(self, other): |
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298 if type(other) is type(self): |
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299 return self.getdata() == other.getdata() |
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300 return False |
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301 |
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302 def __hash__(self): |
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303 return self.getdata().__hash__() |
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304 |
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305 @property |
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306 def IsReduce(self): |
| 186 | 307 """ Check if this item has the dot at the end """ |
| 346 | 308 return not self._is_shift |
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309 |
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310 @property |
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311 def IsShift(self): |
| 186 | 312 """ Check if this item is a shift item, i.e. the dot can proceed """ |
| 346 | 313 return self._is_shift |
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314 |
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315 @property |
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316 def Next(self): |
| 186 | 317 """ Returns the symbol after the dot """ |
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318 return self.production.symbols[self.dotpos] |
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319 |
| 184 | 320 def can_shift_over(self, symbol): |
| 321 """ Determines if this item can shift over the given symbol """ | |
| 322 return self.IsShift and self.Next == symbol | |
| 323 | |
| 324 def shifted(self): | |
| 325 """ Creates a new item that is shifted one position """ | |
| 326 return Item(self.production, self.dotpos + 1, self.look_ahead) | |
| 327 | |
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328 @property |
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329 def NextNext(self): |
| 186 | 330 """ Gets the symbol after the next symbol, or EPS if at the end """ |
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331 if self.dotpos + 1 >= len(self.production.symbols): |
| 184 | 332 return EPS |
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333 else: |
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334 return self.production.symbols[self.dotpos + 1] |
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335 |
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336 def __repr__(self): |
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337 prod = self.production |
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338 predot = ' '.join(prod.symbols[0:self.dotpos]) |
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339 postdot = ' '.join(prod.symbols[self.dotpos:]) |
| 186 | 340 name = prod.name |
| 341 args = (name, predot, postdot, self.look_ahead) | |
| 185 | 342 return '[{0} -> {1} . {2} -> {3}]'.format(*args) |
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343 |
| 179 | 344 |
| 345 class LRParser: | |
| 318 | 346 """ LR parser automata """ |
| 195 | 347 def __init__(self, action_table, goto_table, start_symbol): |
| 184 | 348 self.action_table = action_table |
| 185 | 349 self.goto_table = goto_table |
| 195 | 350 self.start_symbol = start_symbol |
| 184 | 351 |
| 318 | 352 def parse(self, lexer): |
| 191 | 353 """ Parse an iterable with tokens """ |
| 318 | 354 assert hasattr(lexer, 'next_token'), '{0} is no lexer'.format(type(lexer)) |
| 185 | 355 stack = [0] |
| 195 | 356 r_data_stack = [] |
| 318 | 357 look_ahead = lexer.next_token() |
| 191 | 358 assert type(look_ahead) is Token |
| 195 | 359 # TODO: exit on this condition: |
| 360 while stack != [0, self.start_symbol, 2222]: | |
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361 state = stack[-1] # top of stack |
| 191 | 362 key = (state, look_ahead.typ) |
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363 if not key in self.action_table: |
| 194 | 364 raise ParserException('Error parsing at character {0}'.format(look_ahead)) |
| 318 | 365 action = self.action_table[key] |
| 366 if type(action) is Reduce: | |
| 194 | 367 f_args = [] |
| 318 | 368 prod = self.grammar.productions[action.rule] |
| 369 for s in prod.symbols: | |
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370 stack.pop() |
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371 stack.pop() |
| 195 | 372 f_args.append(r_data_stack.pop()) |
| 373 f_args.reverse() | |
| 374 r_data = None | |
| 318 | 375 if prod.f: |
| 376 r_data = prod.f(*f_args) | |
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377 state = stack[-1] |
| 318 | 378 stack.append(prod.name) |
| 379 stack.append(self.goto_table[(state, prod.name)]) | |
| 195 | 380 r_data_stack.append(r_data) |
| 318 | 381 elif type(action) is Shift: |
| 191 | 382 stack.append(look_ahead.typ) |
| 318 | 383 stack.append(action.to_state) |
| 384 r_data_stack.append(look_ahead) | |
| 385 look_ahead = lexer.next_token() | |
| 191 | 386 assert type(look_ahead) is Token |
| 318 | 387 elif type(action) is Accept: |
| 195 | 388 # Pop last rule data off the stack: |
| 389 f_args = [] | |
| 318 | 390 param = self.grammar.productions[action.rule] |
| 195 | 391 for s in param.symbols: |
| 392 stack.pop() | |
| 393 stack.pop() | |
| 394 f_args.append(r_data_stack.pop()) | |
| 395 f_args.reverse() | |
| 396 if param.f: | |
| 318 | 397 ret_val = param.f(*f_args) |
| 398 else: | |
| 399 ret_val = None | |
| 195 | 400 # Break out! |
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401 break |
| 195 | 402 # At exit, the stack must be 1 long |
| 403 # TODO: fix that this holds: | |
| 319 | 404 #assert len(stack) == 1, 'stack {0} not totally reduce'.format(stack) |
| 318 | 405 return ret_val |