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annotate mercurial/parser.py @ 11791:00cde9bddbe4
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author | Nicolas Dumazet <nicdumz.commits@gmail.com> |
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date | Thu, 12 Aug 2010 16:53:23 +0900 |
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11274 | 1 # parser.py - simple top-down operator precedence parser for mercurial |
2 # | |
3 # Copyright 2010 Matt Mackall <mpm@selenic.com> | |
4 # | |
5 # This software may be used and distributed according to the terms of the | |
6 # GNU General Public License version 2 or any later version. | |
7 | |
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8 # see http://effbot.org/zone/simple-top-down-parsing.htm and |
11274 | 9 # http://eli.thegreenplace.net/2010/01/02/top-down-operator-precedence-parsing/ |
10 # for background | |
11 | |
12 # takes a tokenizer and elements | |
13 # tokenizer is an iterator that returns type, value pairs | |
14 # elements is a mapping of types to binding strength, prefix and infix actions | |
15 # an action is a tree node name, a tree label, and an optional match | |
16 # __call__(program) parses program into a labelled tree | |
17 | |
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18 import error |
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19 |
11274 | 20 class parser(object): |
21 def __init__(self, tokenizer, elements, methods=None): | |
22 self._tokenizer = tokenizer | |
23 self._elements = elements | |
24 self._methods = methods | |
25 def _advance(self): | |
26 'advance the tokenizer' | |
27 t = self.current | |
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28 try: |
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29 self.current = self._iter.next() |
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30 except StopIteration: |
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31 pass |
11274 | 32 return t |
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33 def _match(self, m, pos): |
11274 | 34 'make sure the tokenizer matches an end condition' |
35 if self.current[0] != m: | |
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36 raise error.ParseError("unexpected token: %s" % self.current[0], |
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37 self.current[2]) |
11274 | 38 self._advance() |
39 def _parse(self, bind=0): | |
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40 token, value, pos = self._advance() |
11274 | 41 # handle prefix rules on current token |
42 prefix = self._elements[token][1] | |
43 if not prefix: | |
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44 raise error.ParseError("not a prefix: %s" % token, pos) |
11274 | 45 if len(prefix) == 1: |
46 expr = (prefix[0], value) | |
47 else: | |
48 if len(prefix) > 2 and prefix[2] == self.current[0]: | |
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49 self._match(prefix[2], pos) |
11274 | 50 expr = (prefix[0], None) |
51 else: | |
52 expr = (prefix[0], self._parse(prefix[1])) | |
53 if len(prefix) > 2: | |
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54 self._match(prefix[2], pos) |
11274 | 55 # gather tokens until we meet a lower binding strength |
56 while bind < self._elements[self.current[0]][0]: | |
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57 token, value, pos = self._advance() |
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58 e = self._elements[token] |
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59 # check for suffix - next token isn't a valid prefix |
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60 if len(e) == 4 and not self._elements[self.current[0]][1]: |
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61 suffix = e[3] |
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62 expr = (suffix[0], expr) |
11274 | 63 else: |
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64 # handle infix rules |
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65 if len(e) < 3 or not e[2]: |
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66 raise error.ParseError("not an infix: %s" % token, pos) |
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67 infix = e[2] |
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68 if len(infix) == 3 and infix[2] == self.current[0]: |
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69 self._match(infix[2], pos) |
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70 expr = (infix[0], expr, (None)) |
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71 else: |
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72 expr = (infix[0], expr, self._parse(infix[1])) |
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73 if len(infix) == 3: |
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74 self._match(infix[2], pos) |
11274 | 75 return expr |
76 def parse(self, message): | |
77 'generate a parse tree from a message' | |
78 self._iter = self._tokenizer(message) | |
79 self.current = self._iter.next() | |
80 return self._parse() | |
81 def eval(self, tree): | |
82 'recursively evaluate a parse tree using node methods' | |
83 if not isinstance(tree, tuple): | |
84 return tree | |
85 return self._methods[tree[0]](*[self.eval(t) for t in tree[1:]]) | |
86 def __call__(self, message): | |
87 'parse a message into a parse tree and evaluate if methods given' | |
88 t = self.parse(message) | |
89 if self._methods: | |
90 return self.eval(t) | |
91 return t |