Mercurial > hg
view mercurial/parser.py @ 11277:2698a95f3f1b
revset: hook into revrange
author | Matt Mackall <mpm@selenic.com> |
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date | Tue, 01 Jun 2010 11:18:57 -0500 |
parents | 77272d28b53f |
children | 7df88cdf47fd |
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# parser.py - simple top-down operator precedence parser for mercurial # # Copyright 2010 Matt Mackall <mpm@selenic.com> # # This software may be used and distributed according to the terms of the # GNU General Public License version 2 or any later version. # see http://effbot.org/zone/simple-top-down-parsing.txt and # http://eli.thegreenplace.net/2010/01/02/top-down-operator-precedence-parsing/ # for background # takes a tokenizer and elements # tokenizer is an iterator that returns type, value pairs # elements is a mapping of types to binding strength, prefix and infix actions # an action is a tree node name, a tree label, and an optional match # __call__(program) parses program into a labelled tree class parser(object): def __init__(self, tokenizer, elements, methods=None): self._tokenizer = tokenizer self._elements = elements self._methods = methods def _advance(self): 'advance the tokenizer' t = self.current self.current = self._iter.next() return t def _match(self, m): 'make sure the tokenizer matches an end condition' if self.current[0] != m: raise SyntaxError(self.current) self._advance() def _parse(self, bind=0): token, value = self._advance() # handle prefix rules on current token prefix = self._elements[token][1] if not prefix: raise SyntaxError("not a prefix: %s" % token) if len(prefix) == 1: expr = (prefix[0], value) else: if len(prefix) > 2 and prefix[2] == self.current[0]: self._match(prefix[2]) expr = (prefix[0], None) else: expr = (prefix[0], self._parse(prefix[1])) if len(prefix) > 2: self._match(prefix[2]) # gather tokens until we meet a lower binding strength while bind < self._elements[self.current[0]][0]: token, value = self._advance() # handle infix rules infix = self._elements[token][2] if len(infix) == 3 and infix[2] == self.current[0]: self._match(infix[2]) expr = (infix[0], expr, (None)) else: if not infix[0]: raise SyntaxError("not an infix") expr = (infix[0], expr, self._parse(infix[1])) if len(infix) == 3: self._match(infix[2]) return expr def parse(self, message): 'generate a parse tree from a message' self._iter = self._tokenizer(message) self.current = self._iter.next() return self._parse() def eval(self, tree): 'recursively evaluate a parse tree using node methods' if not isinstance(tree, tuple): return tree return self._methods[tree[0]](*[self.eval(t) for t in tree[1:]]) def __call__(self, message): 'parse a message into a parse tree and evaluate if methods given' t = self.parse(message) if self._methods: return self.eval(t) return t