tokenstream.py

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"""\
@file tokenstream.py
@brief Message template parsing utility class

$LicenseInfo:firstyear=2007&license=mit$

Copyright (c) 2007-2008, Linden Research, Inc.

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.
$/LicenseInfo$
"""

import re

class _EOF(object):
    pass

EOF = _EOF()

class _LineMarker(int):
    pass
    
_commentRE = re.compile(r'//.*')
_symbolRE = re.compile(r'[a-zA-Z_][a-zA-Z_0-9]*')
_integerRE = re.compile(r'(0x[0-9A-Fa-f]+|0\d*|[1-9]\d*)')
_floatRE = re.compile(r'\d+(\.\d*)?')


class ParseError(Exception):
    def __init__(self, stream, reason):
        self.line = stream.line
        self.context = stream._context()
        self.reason = reason

    def _contextString(self):    
        c = [ ]
        for t in self.context:
            if isinstance(t, _LineMarker):
                break
            c.append(t)
        return " ".join(c)

    def __str__(self):
        return "line %d: %s @ ... %s" % (
            self.line, self.reason, self._contextString())

    def __nonzero__(self):
        return False


def _optionText(options):
    n = len(options)
    if n == 1:
        return '"%s"' % options[0]
    return '"' + '", "'.join(options[0:(n-1)]) + '" or "' + options[-1] + '"'


class TokenStream(object):
    def __init__(self):
        self.line = 0
        self.tokens = [ ]
    
    def fromString(self, string):
        return self.fromLines(string.split('\n'))
        
    def fromFile(self, file):
        return self.fromLines(file)

    def fromLines(self, lines):
        i = 0
        for line in lines:
            i += 1
            self.tokens.append(_LineMarker(i))
            self.tokens.extend(_commentRE.sub(" ", line).split())
        self._consumeLines()
        return self
    
    def consume(self):
        if not self.tokens:
            return EOF
        t = self.tokens.pop(0)
        self._consumeLines()
        return t
    
    def _consumeLines(self):
        while self.tokens and isinstance(self.tokens[0], _LineMarker):
            self.line = self.tokens.pop(0)
    
    def peek(self):
        if not self.tokens:
            return EOF
        return self.tokens[0]
            
    def want(self, t):
        if t == self.peek():
            return self.consume()
        return ParseError(self, 'expected "%s"' % t)

    def wantOneOf(self, options):
        assert len(options)
        if self.peek() in options:
            return self.consume()
        return ParseError(self, 'expected one of %s' % _optionText(options))

    def wantEOF(self):
        return self.want(EOF)
        
    def wantRE(self, re, message=None):
        t = self.peek()
        if t != EOF:
            m = re.match(t)
            if m and m.end() == len(t):
                return self.consume()
        if not message:
            message = "expected match for r'%s'" % re.pattern
        return ParseError(self, message)
    
    def wantSymbol(self):
        return self.wantRE(_symbolRE, "expected symbol")
    
    def wantInteger(self):
        return self.wantRE(_integerRE, "expected integer")
    
    def wantFloat(self):
        return self.wantRE(_floatRE, "expected float")
    
    def _context(self):
        n = min(5, len(self.tokens))
        return self.tokens[0:n]

    def require(self, t):
        if t:
            return t
        if isinstance(t, ParseError):
            raise t
        else:
            raise ParseError(self, "unmet requirement")

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