173 lines
5.3 KiB
Python
173 lines
5.3 KiB
Python
# Yapps 2.0 Runtime
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#
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# This module is needed to run generated parsers.
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from string import *
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import exceptions
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import re
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class SyntaxError(Exception):
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"""When we run into an unexpected token, this is the exception to use"""
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def __init__(self, pos=-1, msg="Bad Token"):
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self.pos = pos
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self.msg = msg
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def __repr__(self):
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if self.pos < 0: return "#<syntax-error>"
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else: return "SyntaxError[@ char " + `self.pos` + ": " + self.msg + "]"
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class NoMoreTokens(Exception):
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"""Another exception object, for when we run out of tokens"""
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pass
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class Scanner:
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def __init__(self, patterns, ignore, input):
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"""Patterns is [(terminal,regex)...]
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Ignore is [terminal,...];
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Input is a string"""
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self.tokens = []
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self.restrictions = []
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self.input = input
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self.pos = 0
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self.ignore = ignore
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# The stored patterns are a pair (compiled regex,source
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# regex). If the patterns variable passed in to the
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# constructor is None, we assume that the class already has a
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# proper .patterns list constructed
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if patterns is not None:
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self.patterns = []
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for k,r in patterns:
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self.patterns.append( (k, re.compile(r)) )
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def token(self, i, restrict=0):
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"""Get the i'th token, and if i is one past the end, then scan
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for another token; restrict is a list of tokens that
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are allowed, or 0 for any token."""
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if i == len(self.tokens): self.scan(restrict)
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if i < len(self.tokens):
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# Make sure the restriction is more restricted
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if restrict and self.restrictions[i]:
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for r in restrict:
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if r not in self.restrictions[i]:
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raise "Unimplemented: restriction set changed"
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return self.tokens[i]
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raise NoMoreTokens()
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def __repr__(self):
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"""Print the last 10 tokens that have been scanned in"""
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output = ''
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for t in self.tokens[-10:]:
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output = '%s\n (@%s) %s = %s' % (output,t[0],t[2],`t[3]`)
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return output
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def scan(self, restrict):
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"""Should scan another token and add it to the list, self.tokens,
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and add the restriction to self.restrictions"""
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# Keep looking for a token, ignoring any in self.ignore
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while 1:
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# Search the patterns for the longest match, with earlier
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# tokens in the list having preference
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best_match = -1
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best_pat = '(error)'
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for p, regexp in self.patterns:
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# First check to see if we're ignoring this token
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if restrict and p not in restrict and p not in self.ignore:
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continue
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m = regexp.match(self.input, self.pos)
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if m and len(m.group(0)) > best_match:
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# We got a match that's better than the previous one
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best_pat = p
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best_match = len(m.group(0))
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# If we didn't find anything, raise an error
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if best_pat == '(error)' and best_match < 0:
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msg = "Bad Token"
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if restrict:
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msg = "Trying to find one of "+join(restrict,", ")
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raise SyntaxError(self.pos, msg)
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# If we found something that isn't to be ignored, return it
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if best_pat not in self.ignore:
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# Create a token with this data
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token = (self.pos, self.pos+best_match, best_pat,
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self.input[self.pos:self.pos+best_match])
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self.pos = self.pos + best_match
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# Only add this token if it's not in the list
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# (to prevent looping)
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if not self.tokens or token != self.tokens[-1]:
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self.tokens.append(token)
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self.restrictions.append(restrict)
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return
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else:
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# This token should be ignored ..
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self.pos = self.pos + best_match
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class Parser:
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def __init__(self, scanner):
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self._scanner = scanner
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self._pos = 0
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def _peek(self, *types):
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"""Returns the token type for lookahead; if there are any args
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then the list of args is the set of token types to allow"""
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tok = self._scanner.token(self._pos, types)
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return tok[2]
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def _scan(self, type):
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"""Returns the matched text, and moves to the next token"""
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tok = self._scanner.token(self._pos, [type])
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if tok[2] != type:
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raise SyntaxError(tok[0], 'Trying to find '+type)
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self._pos = 1+self._pos
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return tok[3]
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def print_error(input, err, scanner):
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"""This is a really dumb long function to print error messages nicely."""
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p = err.pos
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# Figure out the line number
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line = count(input[:p], '\n')
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print err.msg+" on line "+`line+1`+":"
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# Now try printing part of the line
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text = input[max(p-80,0):p+80]
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p = p - max(p-80,0)
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# Strip to the left
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i = rfind(text[:p],'\n')
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j = rfind(text[:p],'\r')
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if i < 0 or (j < i and j >= 0): i = j
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if i >= 0 and i < p:
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p = p - i - 1
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text = text[i+1:]
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# Strip to the right
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i = find(text,'\n',p)
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j = find(text,'\r',p)
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if i < 0 or (j < i and j >= 0): i = j
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if i >= 0:
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text = text[:i]
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# Now shorten the text
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while len(text) > 70 and p > 60:
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# Cut off 10 chars
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text = "..." + text[10:]
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p = p - 7
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# Now print the string, along with an indicator
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print '> ',text
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print '> ',' '*p + '^'
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print 'List of nearby tokens:', scanner
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def wrap_error_reporter(parser, rule):
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try: return getattr(parser, rule)()
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except SyntaxError, s:
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input = parser._scanner.input
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try:
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print_error(input, s, parser._scanner)
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except ImportError:
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print 'Syntax Error',s.msg,'on line',1+count(input[:s.pos], '\n')
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except NoMoreTokens:
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print 'Could not complete parsing; stopped around here:'
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print parser._scanner
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