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