# Twisted, the Framework of Your Internet
# Copyright (C) 2001 Matthew W. Lefkowitz
#
# This library is free software; you can redistribute it and/or
# modify it under the terms of version 2.1 of the GNU Lesser General Public
# License as published by the Free Software Foundation.
#
# This library is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
# Lesser General Public License for more details.
#
# You should have received a copy of the GNU Lesser General Public
# License along with this library; if not, write to the Free Software
# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
# NOTE!
# NOTE! Actual grammar is at the end of the file
# NOTE!
# HOWTO Generate me:
# 1.) Grab a copy of yapps2: http://theory.stanford.edu/~amitp/Yapps/
# 2.) Hack it to not add a "import yappsrt" in the output file
# 3.) Generate the grammar as usual
"""Run time libraries needed to run parsers generated by Yapps.
This module defines parse-time exception classes, a scanner class, a
base class for parsers produced by Yapps, and a context class that
keeps track of the parse stack.
"""
# TODO: it should be possible to embed yappsrt into the generated
# grammar to make a standalone module.
import sys, re
class SyntaxError(Exception):
"""When we run into an unexpected token, this is the exception to use"""
def __init__(self, charpos=-1, msg="Bad Token", context=None):
Exception.__init__(self)
self.charpos = charpos
self.msg = msg
self.context = context
def __str__(self):
if self.charpos < 0: return 'SyntaxError'
else: return 'SyntaxError@char%s(%s)' % (repr(self.charpos), self.msg)
class NoMoreTokens(Exception):
"""Another exception object, for when we run out of tokens"""
pass
class Scanner:
"""Yapps scanner.
The Yapps scanner can work in context sensitive or context
insensitive modes. The token(i) method is used to retrieve the
i-th token. It takes a restrict set that limits the set of tokens
it is allowed to return. In context sensitive mode, this restrict
set guides the scanner. In context insensitive mode, there is no
restriction (the set is always the full set of tokens).
"""
def __init__(self, patterns, ignore, input):
"""Initialize the scanner.
Parameters:
patterns : [(terminal, uncompiled regex), ...] or None
ignore : [terminal,...]
input : string
If patterns is None, we assume that the subclass has
defined self.patterns : [(terminal, compiled regex), ...].
Note that the patterns parameter expects uncompiled regexes,
whereas the self.patterns field expects compiled regexes.
"""
self.tokens = [] # [(begin char pos, end char pos, token name, matched text), ...]
self.restrictions = []
self.input = input
self.pos = 0
self.ignore = ignore
self.first_line_number = 1
if patterns is not None:
# Compile the regex strings into regex objects
self.patterns = []
for terminal, regex in patterns:
self.patterns.append( (terminal, re.compile(regex)) )
def get_token_pos(self):
"""Get the current token position in the input text."""
return len(self.tokens)
def get_char_pos(self):
"""Get the current char position in the input text."""
return self.pos
def get_prev_char_pos(self, i=None):
"""Get the previous position (one token back) in the input text."""
if self.pos == 0: return 0
if i is None: i = -1
return self.tokens[i][0]
def get_line_number(self):
"""Get the line number of the current position in the input text."""
# TODO: make this work at any token/char position
return self.first_line_number + self.get_input_scanned().count('\n')
def get_column_number(self):
"""Get the column number of the current position in the input text."""
s = self.get_input_scanned()
i = s.rfind('\n') # may be -1, but that's okay in this case
return len(s) - (i+1)
def get_input_scanned(self):
"""Get the portion of the input that has been tokenized."""
return self.input[:self.pos]
def get_input_unscanned(self):
"""Get the portion of the input that has not yet been tokenized."""
return self.input[self.pos:]
def token(self, i, restrict=None):
"""Get the i'th token in the input.
If i is one past the end, then scan for another token.
Args:
restrict : [token, ...] or None; if restrict is None, then any
token is allowed. You may call token(i) more than once.
However, the restrict set may never be larger than what was
passed in on the first call to token(i).
"""
if i == len(self.tokens):
self.scan(restrict)
if i < len(self.tokens):
# Make sure the restriction is more restricted. This
# invariant is needed to avoid ruining tokenization at
# position i+1 and higher.
if restrict and self.restrictions[i]:
for r in restrict:
if r not in self.restrictions[i]:
raise NotImplementedError("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],repr(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:
"""Base class for Yapps-generated parsers.
"""
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+' :'+ ' ,'.join(self._scanner.restrictions[self._pos]))
self._pos = 1 + self._pos
return tok[3]
class Context:
"""Class to represent the parser's call stack.
Every rule creates a Context that links to its parent rule. The
contexts can be used for debugging.
"""
def __init__(self, parent, scanner, tokenpos, rule, args=()):
"""Create a new context.
Args:
parent: Context object or None
scanner: Scanner object
pos: integer (scanner token position)
rule: string (name of the rule)
args: tuple listing parameters to the rule
"""
self.parent = parent
self.scanner = scanner
self.tokenpos = tokenpos
self.rule = rule
self.args = args
def __str__(self):
output = ''
if self.parent: output = str(self.parent) + ' > '
output += self.rule
return output
def print_line_with_pointer(text, p):
"""Print the line of 'text' that includes position 'p',
along with a second line with a single caret (^) at position p"""
# TODO: separate out the logic for determining the line/character
# location from the logic for determining how to display an
# 80-column line to stderr.
# Now try printing part of the line
text = text[max(p-80, 0):p+80]
p = p - max(p-80, 0)
# Strip to the left
i = text[:p].rfind('\n')
j = text[:p].rfind('\r')
if i < 0 or (0 <= j < i): i = j
if 0 <= i < p:
p = p - i - 1
text = text[i+1:]
# Strip to the right
i = text.find('\n', p)
j = text.find('\r', p)
if i < 0 or (0 <= j < i): 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 >>sys.stderr, '> ',text
print >>sys.stderr, '> ',' '*p + '^'
def print_error(input, err, scanner):
"""Print error messages, the parser stack, and the input text -- for human-readable error messages."""
# NOTE: this function assumes 80 columns :-(
# Figure out the line number
line_number = scanner.get_line_number()
column_number = scanner.get_column_number()
print >>sys.stderr, '%d:%d: %s' % (line_number, column_number, err.msg)
context = err.context
if not context:
print_line_with_pointer(input, err.charpos)
while context:
# TODO: add line number
print >>sys.stderr, 'while parsing %s%s:' % (context.rule, tuple(context.args))
print_line_with_pointer(input, context.scanner.get_prev_char_pos(context.tokenpos))
context = context.parent
def wrap_error_reporter(parser, rule):
try:
return getattr(parser, rule)()
except SyntaxError, e:
input = parser._scanner.input
print_error(input, e, parser._scanner)
except NoMoreTokens:
print >>sys.stderr, 'Could not complete parsing; stopped around here:'
print >>sys.stderr, parser._scanner
from twisted.xish.xpath import _Location, _AnyLocation, IndexValue, CompareValue, AttribValue, LiteralValue, Function
%%
parser XPathParser:
ignore: "\\s+"
token INDEX: "[0-9]+"
token WILDCARD: "\*"
token IDENTIFIER: "[a-zA-Z][a-zA-Z0-9_\-]*"
token ATTRIBUTE: "\@[a-zA-Z][a-zA-Z0-9_\-]*"
token FUNCNAME: "[a-zA-Z][a-zA-Z0-9_]*"
token CMP_EQ: "\="
token CMP_NE: "\!\="
token STR_DQ: '"([^"]|(\\"))*?"'
token STR_SQ: "'([^']|(\\'))*?'"
token END: "$"
rule XPATH: PATH {{ result = PATH; current = result }}
( PATH {{ current.childLocation = PATH; current = current.childLocation }} ) * END
{{ return result }}
rule PATH: ("/" {{ result = _Location() }} | "//" {{ result = _AnyLocation() }} )
( IDENTIFIER {{ result.elementName = IDENTIFIER }} | WILDCARD {{ result.elementName = None }} )
( "\[" PREDICATE {{ result.predicates.append(PREDICATE) }} "\]")*
{{ return result }}
rule PREDICATE: EXPR {{ return EXPR }} |
INDEX {{ return IndexValue(INDEX) }}
rule EXPR: VALUE {{ e = VALUE }}
[ CMP VALUE {{ e = CompareValue(e, CMP, VALUE) }} ]
{{ return e }}
rule VALUE: "@" IDENTIFIER {{ return AttribValue(IDENTIFIER) }} |
FUNCNAME {{ f = Function(FUNCNAME); args = [] }}
"\("[ VALUE {{ args.append(VALUE) }}
(
"," VALUE {{ args.append(VALUE) }}
)*
] "\)" {{ f.setParams(*args); return f }} |
STR {{ return LiteralValue(STR[1:len(STR)-1]) }}
rule CMP: (CMP_EQ {{ return CMP_EQ }} | CMP_NE {{ return CMP_NE }})
rule STR: (STR_DQ {{ return STR_DQ }} | STR_SQ {{ return STR_SQ }})