path: root/ply/yacc.py

# -----------------------------------------------------------------------------
# ply: yacc.py
#
# Copyright (C) 2001-2022
# David M. Beazley (Dabeaz LLC)
# All rights reserved.
#
# Latest version: https://github.com/dabeaz/ply
#
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions are
# met:
#
# * Redistributions of source code must retain the above copyright notice,
#   this list of conditions and the following disclaimer.
# * Redistributions in binary form must reproduce the above copyright notice,
#   this list of conditions and the following disclaimer in the documentation
#   and/or other materials provided with the distribution.
# * Neither the name of David Beazley or Dabeaz LLC may be used to
#   endorse or promote products derived from this software without
#   specific prior written permission.
#
# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
# A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
# OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
# -----------------------------------------------------------------------------
#
# This implements an LR parser that is constructed from grammar rules defined
# as Python functions. The grammar is specified by supplying the BNF inside
# Python documentation strings.  The inspiration for this technique was borrowed
# from John Aycock's Spark parsing system.  PLY might be viewed as cross between
# Spark and the GNU bison utility.
#
# The current implementation is only somewhat object-oriented. The
# LR parser itself is defined in terms of an object (which allows multiple
# parsers to co-exist).  However, most of the variables used during table
# construction are defined in terms of global variables.  Users shouldn't
# notice unless they are trying to define multiple parsers at the same
# time using threads (in which case they should have their head examined).
#
# This implementation supports both SLR and LALR(1) parsing.  LALR(1)
# support was originally implemented by Elias Ioup (ezioup@alumni.uchicago.edu),
# using the algorithm found in Aho, Sethi, and Ullman "Compilers: Principles,
# Techniques, and Tools" (The Dragon Book).  LALR(1) has since been replaced
# by the more efficient DeRemer and Pennello algorithm.
#
# :::::::: WARNING :::::::
#
# Construction of LR parsing tables is fairly complicated and expensive.
# To make this module run fast, a *LOT* of work has been put into
# optimization---often at the expensive of readability and what might
# consider to be good Python "coding style."   Modify the code at your
# own risk!
# ----------------------------------------------------------------------------

import re
import types
import sys
import inspect

#-----------------------------------------------------------------------------
#                     === User configurable parameters ===
#
# Change these to modify the default behavior of yacc (if you wish)
#-----------------------------------------------------------------------------

yaccdebug   = False            # Debugging mode.  If set, yacc generates a
                               # a 'parser.out' file in the current directory

debug_file  = 'parser.out'     # Default name of the debugging file
error_count = 3                # Number of symbols that must be shifted to leave recovery mode
resultlimit = 40               # Size limit of results when running in debug mode.

MAXINT = sys.maxsize

# This object is a stand-in for a logging object created by the
# logging module.   PLY will use this by default to create things
# such as the parser.out file.  If a user wants more detailed
# information, they can create their own logging object and pass
# it into PLY.

class PlyLogger(object):
    def __init__(self, f):
        self.f = f

    def debug(self, msg, *args, **kwargs):
        self.f.write((msg % args) + '\n')

    info = debug

    def warning(self, msg, *args, **kwargs):
        self.f.write('WARNING: ' + (msg % args) + '\n')

    def error(self, msg, *args, **kwargs):
        self.f.write('ERROR: ' + (msg % args) + '\n')

    critical = debug

# Null logger is used when no output is generated. Does nothing.
class NullLogger(object):
    def __getattribute__(self, name):
        return self

    def __call__(self, *args, **kwargs):
        return self

# Exception raised for yacc-related errors
class YaccError(Exception):
    pass

# Format the result message that the parser produces when running in debug mode.
def format_result(r):
    repr_str = repr(r)
    if '\n' in repr_str:
        repr_str = repr(repr_str)
    if len(repr_str) > resultlimit:
        repr_str = repr_str[:resultlimit] + ' ...'
    result = '<%s @ 0x%x> (%s)' % (type(r).__name__, id(r), repr_str)
    return result

# Format stack entries when the parser is running in debug mode
def format_stack_entry(r):
    repr_str = repr(r)
    if '\n' in repr_str:
        repr_str = repr(repr_str)
    if len(repr_str) < 16:
        return repr_str
    else:
        return '<%s @ 0x%x>' % (type(r).__name__, id(r))

#-----------------------------------------------------------------------------
#                        ===  LR Parsing Engine ===
#
# The following classes are used for the LR parser itself.  These are not
# used during table construction and are independent of the actual LR
# table generation algorithm
#-----------------------------------------------------------------------------

# This class is used to hold non-terminal grammar symbols during parsing.
# It normally has the following attributes set:
#        .type       = Grammar symbol type
#        .value      = Symbol value
#        .lineno     = Starting line number
#        .endlineno  = Ending line number (optional, set automatically)
#        .lexpos     = Starting lex position
#        .endlexpos  = Ending lex position (optional, set automatically)

class YaccSymbol:
    def __str__(self):
        return self.type

    def __repr__(self):
        return str(self)

# This class is a wrapper around the objects actually passed to each
# grammar rule.   Index lookup and assignment actually assign the
# .value attribute of the underlying YaccSymbol object.
# The lineno() method returns the line number of a given
# item (or 0 if not defined).   The linespan() method returns
# a tuple of (startline,endline) representing the range of lines
# for a symbol.  The lexspan() method returns a tuple (lexpos,endlexpos)
# representing the range of positional information for a symbol.

class YaccProduction:
    def __init__(self, s, stack=None):
        self.slice = s
        self.stack = stack
        self.lexer = None
        self.parser = None

    def __getitem__(self, n):
        if isinstance(n, slice):
            return [s.value for s in self.slice[n]]
        elif n >= 0:
            return self.slice[n].value
        else:
            return self.stack[n].value

    def __setitem__(self, n, v):
        self.slice[n].value = v

    def __getslice__(self, i, j):
        return [s.value for s in self.slice[i:j]]

    def __len__(self):
        return len(self.slice)

    def lineno(self, n):
        return getattr(self.slice[n], 'lineno', 0)

    def set_lineno(self, n, lineno):
        self.slice[n].lineno = lineno

    def linespan(self, n):
        startline = getattr(self.slice[n], 'lineno', 0)
        endline = getattr(self.slice[n], 'endlineno', startline)
        return startline, endline

    def lexpos(self, n):
        return getattr(self.slice[n], 'lexpos', 0)

    def set_lexpos(self, n, lexpos):
        self.slice[n].lexpos = lexpos

    def lexspan(self, n):
        startpos = getattr(self.slice[n], 'lexpos', 0)
        endpos = getattr(self.slice[n], 'endlexpos', startpos)
        return startpos, endpos

    def error(self):
        raise SyntaxError

# -----------------------------------------------------------------------------
#                               == LRParser ==
#
# The LR Parsing engine.
# -----------------------------------------------------------------------------

class LRParser:
    def __init__(self, lrtab, errorf):
        self.productions = lrtab.lr_productions
        self.action = lrtab.lr_action
        self.goto = lrtab.lr_goto
        self.errorfunc = errorf
        self.set_defaulted_states()
        self.errorok = True

    def errok(self):
        self.errorok = True

    def restart(self):
        del self.statestack[:]
        del self.symstack[:]
        sym = YaccSymbol()
        sym.type = '$end'
        self.symstack.append(sym)
        self.statestack.append(0)

    # Defaulted state support.
    # This method identifies parser states where there is only one possible reduction action.
    # For such states, the parser can make a choose to make a rule reduction without consuming
    # the next look-ahead token.  This delayed invocation of the tokenizer can be useful in
    # certain kinds of advanced parsing situations where the lexer and parser interact with
    # each other or change states (i.e., manipulation of scope, lexer states, etc.).
    #
    # See:  http://www.gnu.org/software/bison/manual/html_node/Default-Reductions.html#Default-Reductions
    def set_defaulted_states(self):
        self.defaulted_states = {}
        for state, actions in self.action.items():
            rules = list(actions.values())
            if len(rules) == 1 and rules[0] < 0:
                self.defaulted_states[state] = rules[0]

    def disable_defaulted_states(self):
        self.defaulted_states = {}

    # parse().
    #
    # This is the core parsing engine.  To operate, it requires a lexer object.
    # Two options are provided.  The debug flag turns on debugging so that you can
    # see the various rule reductions and parsing steps.  tracking turns on position
    # tracking.  In this mode, symbols will record the starting/ending line number and
    # character index.

    def parse(self, input=None, lexer=None, debug=False, tracking=False):
        # If debugging has been specified as a flag, turn it into a logging object
        if isinstance(debug, int) and debug:
            debug = PlyLogger(sys.stderr)

        lookahead = None                         # Current lookahead symbol
        lookaheadstack = []                      # Stack of lookahead symbols
        actions = self.action                    # Local reference to action table (to avoid lookup on self.)
        goto    = self.goto                      # Local reference to goto table (to avoid lookup on self.)
        prod    = self.productions               # Local reference to production list (to avoid lookup on self.)
        defaulted_states = self.defaulted_states # Local reference to defaulted states
        pslice  = YaccProduction(None)           # Production object passed to grammar rules
        errorcount = 0                           # Used during error recovery

        if debug:
            debug.info('PLY: PARSE DEBUG START')

        # If no lexer was given, we will try to use the lex module
        if not lexer:
            from . import lex
            lexer = lex.lexer

        # Set up the lexer and parser objects on pslice
        pslice.lexer = lexer
        pslice.parser = self

        # If input was supplied, pass to lexer
        if input is not None:
            lexer.input(input)

        # Set the token function
        get_token = self.token = lexer.token

        # Set up the state and symbol stacks
        statestack = self.statestack = []   # Stack of parsing states
        symstack = self.symstack = []       # Stack of grammar symbols
        pslice.stack = symstack             # Put in the production
        errtoken   = None                   # Err token

        # The start state is assumed to be (0,$end)

        statestack.append(0)
        sym = YaccSymbol()
        sym.type = '$end'
        symstack.append(sym)
        state = 0
        while True:
            # Get the next symbol on the input.  If a lookahead symbol
            # is already set, we just use that. Otherwise, we'll pull
            # the next token off of the lookaheadstack or from the lexer

            if debug:
                debug.debug('State  : %s', state)

            if state not in defaulted_states:
                if not lookahead:
                    if not lookaheadstack:
                        lookahead = get_token()     # Get the next token
                    else:
                        lookahead = lookaheadstack.pop()
                    if not lookahead:
                        lookahead = YaccSymbol()
                        lookahead.type = '$end'

                # Check the action table
                ltype = lookahead.type
                t = actions[state].get(ltype)
            else:
                t = defaulted_states[state]
                if debug:
                    debug.debug('Defaulted state %s: Reduce using %d', state, -t)

            if debug:
                debug.debug('Stack  : %s',
                            ('%s . %s' % (' '.join([xx.type for xx in symstack][1:]), str(lookahead))).lstrip())

            if t is not None:
                if t > 0:
                    # shift a symbol on the stack
                    statestack.append(t)
                    state = t

                    if debug:
                        debug.debug('Action : Shift and goto state %s', t)

                    symstack.append(lookahead)
                    lookahead = None

                    # Decrease error count on successful shift
                    if errorcount:
                        errorcount -= 1
                    continue

                if t < 0:
                    # reduce a symbol on the stack, emit a production
                    p = prod[-t]
                    pname = p.name
                    plen  = p.len

                    # Get production function
                    sym = YaccSymbol()
                    sym.type = pname       # Production name
                    sym.value = None

                    if debug:
                        if plen:
                            debug.info('Action : Reduce rule [%s] with %s and goto state %d', p.str,
                                       '['+','.join([format_stack_entry(_v.value) for _v in symstack[-plen:]])+']',
                                       goto[statestack[-1-plen]][pname])
                        else:
                            debug.info('Action : Reduce rule [%s] with %s and goto state %d', p.str, [],
                                       goto[statestack[-1]][pname])

                    if plen:
                        targ = symstack[-plen-1:]
                        targ[0] = sym

                        if tracking:
                            t1 = targ[1]
                            sym.lineno = t1.lineno
                            sym.lexpos = t1.lexpos
                            t1 = targ[-1]
                            sym.endlineno = getattr(t1, 'endlineno', t1.lineno)
                            sym.endlexpos = getattr(t1, 'endlexpos', t1.lexpos)

                        # !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
                        # The code enclosed in this section is duplicated
                        # below as a performance optimization.  Make sure
                        # changes get made in both locations.

                        pslice.slice = targ

                        try:
                            # Call the grammar rule with our special slice object
                            del symstack[-plen:]
                            self.state = state
                            p.callable(pslice)
                            del statestack[-plen:]
                            if debug:
                                debug.info('Result : %s', format_result(pslice[0]))
                            symstack.append(sym)
                            state = goto[statestack[-1]][pname]
                            statestack.append(state)
                        except SyntaxError:
                            # If an error was set. Enter error recovery state
                            lookaheadstack.append(lookahead)    # Save the current lookahead token
                            symstack.extend(targ[1:-1])         # Put the production slice back on the stack
                            statestack.pop()                    # Pop back one state (before the reduce)
                            state = statestack[-1]
                            sym.type = 'error'
                            sym.value = 'error'
                            lookahead = sym
                            errorcount = error_count
                            self.errorok = False

                        continue

                    else:

                        if tracking:
                            sym.lineno = lexer.lineno
                            sym.lexpos = lexer.lexpos

                        targ = [sym]

                        # !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
                        # The code enclosed in this section is duplicated
                        # above as a performance optimization.  Make sure
                        # changes get made in both locations.

                        pslice.slice = targ

                        try:
                            # Call the grammar rule with our special slice object
                            self.state = state
                            p.callable(pslice)
                            if debug:
                                debug.info('Result : %s', format_result(pslice[0]))
                            symstack.append(sym)
                            state = goto[statestack[-1]][pname]
                            statestack.append(state)
                        except SyntaxError:
                            # If an error was set. Enter error recovery state
                            lookaheadstack.append(lookahead)    # Save the current lookahead token
                            statestack.pop()                    # Pop back one state (before the reduce)
                            state = statestack[-1]
                            sym.type = 'error'
                            sym.value = 'error'
                            lookahead = sym
                            errorcount = error_count
                            self.errorok = False

                        continue

                if t == 0:
                    n = symstack[-1]
                    result = getattr(n, 'value', None)

                    if debug:
                        debug.info('Done   : Returning %s', format_result(result))
                        debug.info('PLY: PARSE DEBUG END')

                    return result

            if t is None:

                if debug:
                    debug.error('Error  : %s',
                                ('%s . %s' % (' '.join([xx.type for xx in symstack][1:]), str(lookahead))).lstrip())

                # We have some kind of parsing error here.  To handle
                # this, we are going to push the current token onto
                # the tokenstack and replace it with an 'error' token.
                # If there are any synchronization rules, they may
                # catch it.
                #
                # In addition to pushing the error token, we call call
                # the user defined p_error() function if this is the
                # first syntax error.  This function is only called if
                # errorcount == 0.
                if errorcount == 0 or self.errorok:
                    errorcount = error_count
                    self.errorok = False
                    errtoken = lookahead
                    if errtoken.type == '$end':
                        errtoken = None               # End of file!
                    if self.errorfunc:
                        if errtoken and not hasattr(errtoken, 'lexer'):
                            errtoken.lexer = lexer
                        self.state = state
                        tok = self.errorfunc(errtoken)
                        if self.errorok:
                            # User must have done some kind of panic
                            # mode recovery on their own.  The
                            # returned token is the next lookahead
                            lookahead = tok
                            errtoken = None
                            continue
                    else:
                        if errtoken:
                            if hasattr(errtoken, 'lineno'):
                                lineno = lookahead.lineno
                            else:
                                lineno = 0
                            if lineno:
                                sys.stderr.write('yacc: Syntax error at line %d, token=%s\n' % (lineno, errtoken.type))
                            else:
                                sys.stderr.write('yacc: Syntax error, token=%s' % errtoken.type)
                        else:
                            sys.stderr.write('yacc: Parse error in input. EOF\n')
                            return

                else:
                    errorcount = error_count

                # case 1:  the statestack only has 1 entry on it.  If we're in this state, the
                # entire parse has been rolled back and we're completely hosed.   The token is
                # discarded and we just keep going.

                if len(statestack) <= 1 and lookahead.type != '$end':
                    lookahead = None
                    errtoken = None
                    state = 0
                    # Nuke the pushback stack
                    del lookaheadstack[:]
                    continue

                # case 2: the statestack has a couple of entries on it, but we're
                # at the end of the file. nuke the top entry and generate an error token

                # Start nuking entries on the stack
                if lookahead.type == '$end':
                    # Whoa. We're really hosed here. Bail out
                    return

                if lookahead.type != 'error':
                    sym = symstack[-1]
                    if sym.type == 'error':
                        # Hmmm. Error is on top of stack, we'll just nuke input
                        # symbol and continue
                        if tracking:
                            sym.endlineno = getattr(lookahead, 'lineno', sym.lineno)
                            sym.endlexpos = getattr(lookahead, 'lexpos', sym.lexpos)
                        lookahead = None
                        continue

                    # Create the error symbol for the first time and make it the new lookahead symbol
                    t = YaccSymbol()
                    t.type = 'error'

                    if hasattr(lookahead, 'lineno'):
                        t.lineno = t.endlineno = lookahead.lineno
                    if hasattr(lookahead, 'lexpos'):
                        t.lexpos = t.endlexpos = lookahead.lexpos
                    t.value = lookahead
                    lookaheadstack.append(lookahead)
                    lookahead = t
                else:
                    sym = symstack.pop()
                    if tracking:
                        lookahead.lineno = sym.lineno
                        lookahead.lexpos = sym.lexpos
                    statestack.pop()
                    state = statestack[-1]

                continue

            # If we'r here, something really bad happened
            raise RuntimeError('yacc: internal parser error!!!\n')

# -----------------------------------------------------------------------------
#                          === Grammar Representation ===
#
# The following functions, classes, and variables are used to represent and
# manipulate the rules that make up a grammar.
# -----------------------------------------------------------------------------

# regex matching identifiers
_is_identifier = re.compile(r'^[a-zA-Z0-9_-]+$')

# -----------------------------------------------------------------------------
# class Production:
#
# This class stores the raw information about a single production or grammar rule.
# A grammar rule refers to a specification such as this:
#
#       expr : expr PLUS term
#
# Here are the basic attributes defined on all productions
#
#       name     - Name of the production.  For example 'expr'
#       prod     - A list of symbols on the right side ['expr','PLUS','term']
#       prec     - Production precedence level
#       number   - Production number.
#       func     - Function that executes on reduce
#       file     - File where production function is defined
#       lineno   - Line number where production function is defined
#
# The following attributes are defined or optional.
#
#       len       - Length of the production (number of symbols on right hand side)
#       usyms     - Set of unique symbols found in the production
# -----------------------------------------------------------------------------

class Production(object):
    reduced = 0
    def __init__(self, number, name, prod, precedence=('right', 0), func=None, file='', line=0):
        self.name     = name
        self.prod     = tuple(prod)
        self.number   = number
        self.func     = func
        self.callable = None
        self.file     = file
        self.line     = line
        self.prec     = precedence

        # Internal settings used during table construction

        self.len  = len(self.prod)   # Length of the production

        # Create a list of unique production symbols used in the production
        self.usyms = []
        for s in self.prod:
            if s not in self.usyms:
                self.usyms.append(s)

        # List of all LR items for the production
        self.lr_items = []
        self.lr_next = None

        # Create a string representation
        if self.prod:
            self.str = '%s -> %s' % (self.name, ' '.join(self.prod))
        else:
            self.str = '%s -> <empty>' % self.name

    def __str__(self):
        return self.str

    def __repr__(self):
        return 'Production(' + str(self) + ')'

    def __len__(self):
        return len(self.prod)

    def __nonzero__(self):
        return 1

    def __getitem__(self, index):
        return self.prod[index]

    # Return the nth lr_item from the production (or None if at the end)
    def lr_item(self, n):
        if n > len(self.prod):
            return None
        p = LRItem(self, n)
        # Precompute the list of productions immediately following.
        try:
            p.lr_after = self.Prodnames[p.prod[n+1]]
        except (IndexError, KeyError):
            p.lr_after = []
        try:
            p.lr_before = p.prod[n-1]
        except IndexError:
            p.lr_before = None
        return p

    # Bind the production function name to a callable
    def bind(self, pdict):
        if self.func:
            self.callable = pdict[self.func]

# -----------------------------------------------------------------------------
# class LRItem
#
# This class represents a specific stage of parsing a production rule.  For
# example:
#
#       expr : expr . PLUS term
#
# In the above, the "." represents the current location of the parse.  Here
# basic attributes:
#
#       name       - Name of the production.  For example 'expr'
#       prod       - A list of symbols on the right side ['expr','.', 'PLUS','term']
#       number     - Production number.
#
#       lr_next      Next LR item. Example, if we are ' expr -> expr . PLUS term'
#                    then lr_next refers to 'expr -> expr PLUS . term'
#       lr_index   - LR item index (location of the ".") in the prod list.
#       lookaheads - LALR lookahead symbols for this item
#       len        - Length of the production (number of symbols on right hand side)
#       lr_after    - List of all productions that immediately follow
#       lr_before   - Grammar symbol immediately before
# -----------------------------------------------------------------------------

class LRItem(object):
    def __init__(self, p, n):
        self.name       = p.name
        self.prod       = list(p.prod)
        self.number     = p.number
        self.lr_index   = n
        self.lookaheads = {}
        self.prod.insert(n, '.')
        self.prod       = tuple(self.prod)
        self.len        = len(self.prod)
        self.usyms      = p.usyms

    def __str__(self):
        if self.prod:
            s = '%s -> %s' % (self.name, ' '.join(self.prod))
        else:
            s = '%s -> <empty>' % self.name
        return s

    def __repr__(self):
        return 'LRItem(' + str(self) + ')'

# -----------------------------------------------------------------------------
# rightmost_terminal()
#
# Return the rightmost terminal from a list of symbols.  Used in add_production()
# -----------------------------------------------------------------------------
def rightmost_terminal(symbols, terminals):
    i = len(symbols) - 1
    while i >= 0:
        if symbols[i] in terminals:
            return symbols[i]
        i -= 1
    return None

# -----------------------------------------------------------------------------
#                           === GRAMMAR CLASS ===
#
# The following class represents the contents of the specified grammar along
# with various computed properties such as first sets, follow sets, LR items, etc.
# This data is used for critical parts of the table generation process later.
# -----------------------------------------------------------------------------

class GrammarError(YaccError):
    pass

class Grammar(object):
    def __init__(self, terminals):
        self.Productions  = [None]  # A list of all of the productions.  The first
                                    # entry is always reserved for the purpose of
                                    # building an augmented grammar

        self.Prodnames    = {}      # A dictionary mapping the names of nonterminals to a list of all
                                    # productions of that nonterminal.

        self.Prodmap      = {}      # A dictionary that is only used to detect duplicate
                                    # productions.

        self.Terminals    = {}      # A dictionary mapping the names of terminal symbols to a
                                    # list of the rules where they are used.

        for term in terminals:
            self.Terminals[term] = []

        self.Terminals['error'] = []

        self.Nonterminals = {}      # A dictionary mapping names of nonterminals to a list
                                    # of rule numbers where they are used.

        self.First        = {}      # A dictionary of precomputed FIRST(x) symbols

        self.Follow       = {}      # A dictionary of precomputed FOLLOW(x) symbols

        self.Precedence   = {}      # Precedence rules for each terminal. Contains tuples of the
                                    # form ('right',level) or ('nonassoc', level) or ('left',level)

        self.UsedPrecedence = set() # Precedence rules that were actually used by the grammer.
                                    # This is only used to provide error checking and to generate
                                    # a warning about unused precedence rules.

        self.Start = None           # Starting symbol for the grammar


    def __len__(self):
        return len(self.Productions)

    def __getitem__(self, index):
        return self.Productions[index]

    # -----------------------------------------------------------------------------
    # set_precedence()
    #
    # Sets the precedence for a given terminal. assoc is the associativity such as
    # 'left','right', or 'nonassoc'.  level is a numeric level.
    #
    # -----------------------------------------------------------------------------

    def set_precedence(self, term, assoc, level):
        assert self.Productions == [None], 'Must call set_precedence() before add_production()'
        if term in self.Precedence:
            raise GrammarError('Precedence already specified for terminal %r' % term)
        if assoc not in ['left', 'right', 'nonassoc']:
            raise GrammarError("Associativity must be one of 'left','right', or 'nonassoc'")
        self.Precedence[term] = (assoc, level)

    # -----------------------------------------------------------------------------
    # add_production()
    #
    # Given an action function, this function assembles a production rule and
    # computes its precedence level.
    #
    # The production rule is supplied as a list of symbols.   For example,
    # a rule such as 'expr : expr PLUS term' has a production name of 'expr' and
    # symbols ['expr','PLUS','term'].
    #
    # Precedence is determined by the precedence of the right-most non-terminal
    # or the precedence of a terminal specified by %prec.
    #
    # A variety of error checks are performed to make sure production symbols
    # are valid and that %prec is used correctly.
    # -----------------------------------------------------------------------------

    def add_production(self, prodname, syms, func=None, file='', line=0):

        if prodname in self.Terminals:
            raise GrammarError('%s:%d: Illegal rule name %r. Already defined as a token' % (file, line, prodname))
        if prodname == 'error':
            raise GrammarError('%s:%d: Illegal rule name %r. error is a reserved word' % (file, line, prodname))
        if not _is_identifier.match(prodname):
            raise GrammarError('%s:%d: Illegal rule name %r' % (file, line, prodname))

        # Look for literal tokens
        for n, s in enumerate(syms):
            if s[0] in "'\"":
                try:
                    c = eval(s)
                    if (len(c) > 1):
                        raise GrammarError('%s:%d: Literal token %s in rule %r may only be a single character' %
                                           (file, line, s, prodname))
                    if c not in self.Terminals:
                        self.Terminals[c] = []
                    syms[n] = c
                    continue
                except SyntaxError:
                    pass
            if not _is_identifier.match(s) and s != '%prec':
                raise GrammarError('%s:%d: Illegal name %r in rule %r' % (file, line, s, prodname))

        # Determine the precedence level
        if '%prec' in syms:
            if syms[-1] == '%prec':
                raise GrammarError('%s:%d: Syntax error. Nothing follows %%prec' % (file, line))
            if syms[-2] != '%prec':
                raise GrammarError('%s:%d: Syntax error. %%prec can only appear at the end of a grammar rule' %
                                   (file, line))
            precname = syms[-1]
            prodprec = self.Precedence.get(precname)
            if not prodprec:
                raise GrammarError('%s:%d: Nothing known about the precedence of %r' % (file, line, precname))
            else:
                self.UsedPrecedence.add(precname)
            del syms[-2:]     # Drop %prec from the rule
        else:
            # If no %prec, precedence is determined by the rightmost terminal symbol
            precname = rightmost_terminal(syms, self.Terminals)
            prodprec = self.Precedence.get(precname, ('right', 0))

        # See if the rule is already in the rulemap
        map = '%s -> %s' % (prodname, syms)
        if map in self.Prodmap:
            m = self.Prodmap[map]
            raise GrammarError('%s:%d: Duplicate rule %s. ' % (file, line, m) +
                               'Previous definition at %s:%d' % (m.file, m.line))

        # From this point on, everything is valid.  Create a new Production instance
        pnumber  = len(self.Productions)
        if prodname not in self.Nonterminals:
            self.Nonterminals[prodname] = []

        # Add the production number to Terminals and Nonterminals
        for t in syms:
            if t in self.Terminals:
                self.Terminals[t].append(pnumber)
            else:
                if t not in self.Nonterminals:
                    self.Nonterminals[t] = []
                self.Nonterminals[t].append(pnumber)

        # Create a production and add it to the list of productions
        p = Production(pnumber, prodname, syms, prodprec, func, file, line)
        self.Productions.append(p)
        self.Prodmap[map] = p

        # Add to the global productions list
        try:
            self.Prodnames[prodname].append(p)
        except KeyError:
            self.Prodnames[prodname] = [p]

    # -----------------------------------------------------------------------------
    # set_start()
    #
    # Sets the starting symbol and creates the augmented grammar.  Production
    # rule 0 is S' -> start where start is the start symbol.
    # -----------------------------------------------------------------------------

    def set_start(self, start=None):
        if not start:
            start = self.Productions[1].name
        if start not in self.Nonterminals:
            raise GrammarError('start symbol %s undefined' % start)
        self.Productions[0] = Production(0, "S'", [start])
        self.Nonterminals[start].append(0)
        self.Start = start

    # -----------------------------------------------------------------------------
    # find_unreachable()
    #
    # Find all of the nonterminal symbols that can't be reached from the starting
    # symbol.  Returns a list of nonterminals that can't be reached.
    # -----------------------------------------------------------------------------

    def find_unreachable(self):

        # Mark all symbols that are reachable from a symbol s
        def mark_reachable_from(s):
            if s in reachable:
                return
            reachable.add(s)
            for p in self.Prodnames.get(s, []):
                for r in p.prod:
                    mark_reachable_from(r)

        reachable = set()
        mark_reachable_from(self.Productions[0].prod[0])
        return [s for s in self.Nonterminals if s not in reachable]

    # -----------------------------------------------------------------------------
    # infinite_cycles()
    #
    # This function looks at the various parsing rules and tries to detect
    # infinite recursion cycles (grammar rules where there is no possible way
    # to derive a string of only terminals).
    # -----------------------------------------------------------------------------

    def infinite_cycles(self):
        terminates = {}

        # Terminals:
        for t in self.Terminals:
            terminates[t] = True

        terminates['$end'] = True

        # Nonterminals:

        # Initialize to false:
        for n in self.Nonterminals:
            terminates[n] = False

        # Then propagate termination until no change:
        while True:
            some_change = False
            for (n, pl) in self.Prodnames.items():
                # Nonterminal n terminates iff any of its productions terminates.
                for p in pl:
                    # Production p terminates iff all of its rhs symbols terminate.
                    for s in p.prod:
                        if not terminates[s]:
                            # The symbol s does not terminate,
                            # so production p does not terminate.
                            p_terminates = False
                            break
                    else:
                        # didn't break from the loop,
                        # so every symbol s terminates
                        # so production p terminates.
                        p_terminates = True

                    if p_terminates:
                        # symbol n terminates!
                        if not terminates[n]:
                            terminates[n] = True
                            some_change = True
                        # Don't need to consider any more productions for this n.
                        break

            if not some_change:
                break

        infinite = []
        for (s, term) in terminates.items():
            if not term:
                if s not in self.Prodnames and s not in self.Terminals and s != 'error':
                    # s is used-but-not-defined, and we've already warned of that,
                    # so it would be overkill to say that it's also non-terminating.
                    pass
                else:
                    infinite.append(s)

        return infinite

    # -----------------------------------------------------------------------------
    # undefined_symbols()
    #
    # Find all symbols that were used the grammar, but not defined as tokens or
    # grammar rules.  Returns a list of tuples (sym, prod) where sym in the symbol
    # and prod is the production where the symbol was used.
    # -----------------------------------------------------------------------------
    def undefined_symbols(self):
        result = []
        for p in self.Productions:
            if not p:
                continue

            for s in p.prod:
                if s not in self.Prodnames and s not in self.Terminals and s != 'error':
                    result.append((s, p))
        return result

    # -----------------------------------------------------------------------------
    # unused_terminals()
    #
    # Find all terminals that were defined, but not used by the grammar.  Returns
    # a list of all symbols.
    # -----------------------------------------------------------------------------
    def unused_terminals(self):
        unused_tok = []
        for s, v in self.Terminals.items():
            if s != 'error' and not v:
                unused_tok.append(s)

        return unused_tok

    # ------------------------------------------------------------------------------
    # unused_rules()
    #
    # Find all grammar rules that were defined,  but not used (maybe not reachable)
    # Returns a list of productions.
    # ------------------------------------------------------------------------------

    def unused_rules(self):
        unused_prod = []
        for s, v in self.Nonterminals.items():
            if not v:
                p = self.Prodnames[s][0]
                unused_prod.append(p)
        return unused_prod

    # -----------------------------------------------------------------------------
    # unused_precedence()
    #
    # Returns a list of tuples (term,precedence) corresponding to precedence
    # rules that were never used by the grammar.  term is the name of the terminal
    # on which precedence was applied and precedence is a string such as 'left' or
    # 'right' corresponding to the type of precedence.
    # -----------------------------------------------------------------------------

    def unused_precedence(self):
        unused = []
        for termname in self.Precedence:
            if not (termname in self.Terminals or termname in self.UsedPrecedence):
                unused.append((termname, self.Precedence[termname][0]))

        return unused

    # -------------------------------------------------------------------------
    # _first()
    #
    # Compute the value of FIRST1(beta) where beta is a tuple of symbols.
    #
    # During execution of compute_first1, the result may be incomplete.
    # Afterward (e.g., when called from compute_follow()), it will be complete.
    # -------------------------------------------------------------------------
    def _first(self, beta):

        # We are computing First(x1,x2,x3,...,xn)
        result = []
        for x in beta:
            x_produces_empty = False

            # Add all the non-<empty> symbols of First[x] to the result.
            for f in self.First[x]:
                if f == '<empty>':
                    x_produces_empty = True
                else:
                    if f not in result:
                        result.append(f)

            if x_produces_empty:
                # We have to consider the next x in beta,
                # i.e. stay in the loop.
                pass
            else:
                # We don't have to consider any further symbols in beta.
                break
        else:
            # There was no 'break' from the loop,
            # so x_produces_empty was true for all x in beta,
            # so beta produces empty as well.
            result.append('<empty>')

        return result

    # -------------------------------------------------------------------------
    # compute_first()
    #
    # Compute the value of FIRST1(X) for all symbols
    # -------------------------------------------------------------------------
    def compute_first(self):
        if self.First:
            return self.First

        # Terminals:
        for t in self.Terminals:
            self.First[t] = [t]

        self.First['$end'] = ['$end']

        # Nonterminals:

        # Initialize to the empty set:
        for n in self.Nonterminals:
            self.First[n] = []

        # Then propagate symbols until no change:
        while True:
            some_change = False
            for n in self.Nonterminals:
                for p in self.Prodnames[n]:
                    for f in self._first(p.prod):
                        if f not in self.First[n]:
                            self.First[n].append(f)
                            some_change = True
            if not some_change:
                break

        return self.First

    # ---------------------------------------------------------------------
    # compute_follow()
    #
    # Computes all of the follow sets for every non-terminal symbol.  The
    # follow set is the set of all symbols that might follow a given
    # non-terminal.  See the Dragon book, 2nd Ed. p. 189.
    # ---------------------------------------------------------------------
    def compute_follow(self, start=None):
        # If already computed, return the result
        if self.Follow:
            return self.Follow

        # If first sets not computed yet, do that first.
        if not self.First:
            self.compute_first()

        # Add '$end' to the follow list of the start symbol
        for k in self.Nonterminals:
            self.Follow[k] = []

        if not start:
            start = self.Productions[1].name

        self.Follow[start] = ['$end']

        while True:
            didadd = False
            for p in self.Productions[1:]:
                # Here is the production set
                for i, B in enumerate(p.prod):
                    if B in self.Nonterminals:
                        # Okay. We got a non-terminal in a production
                        fst = self._first(p.prod[i+1:])
                        hasempty = False
                        for f in fst:
                            if f != '<empty>' and f not in self.Follow[B]:
                                self.Follow[B].append(f)
                                didadd = True
                            if f == '<empty>':
                                hasempty = True
                        if hasempty or i == (len(p.prod)-1):
                            # Add elements of follow(a) to follow(b)
                            for f in self.Follow[p.name]:
                                if f not in self.Follow[B]:
                                    self.Follow[B].append(f)
                                    didadd = True
            if not didadd:
                break
        return self.Follow


    # -----------------------------------------------------------------------------
    # build_lritems()
    #
    # This function walks the list of productions and builds a complete set of the
    # LR items.  The LR items are stored in two ways:  First, they are uniquely
    # numbered and placed in the list _lritems.  Second, a linked list of LR items
    # is built for each production.  For example:
    #
    #   E -> E PLUS E
    #
    # Creates the list
    #
    #  [E -> . E PLUS E, E -> E . PLUS E, E -> E PLUS . E, E -> E PLUS E . ]
    # -----------------------------------------------------------------------------

    def build_lritems(self):
        for p in self.Productions:
            lastlri = p
            i = 0
            lr_items = []
            while True:
                if i > len(p):
                    lri = None
                else:
                    lri = LRItem(p, i)
                    # Precompute the list of productions immediately following
                    try:
                        lri.lr_after = self.Prodnames[lri.prod[i+1]]
                    except (IndexError, KeyError):
                        lri.lr_after = []
                    try:
                        lri.lr_before = lri.prod[i-1]
                    except IndexError:
                        lri.lr_before = None

                lastlri.lr_next = lri
                if not lri:
                    break
                lr_items.append(lri)
                lastlri = lri
                i += 1
            p.lr_items = lr_items

# -----------------------------------------------------------------------------
#                           === LR Generator ===
#
# The following classes and functions are used to generate LR parsing tables on
# a grammar.
# -----------------------------------------------------------------------------

# -----------------------------------------------------------------------------
# digraph()
# traverse()
#
# The following two functions are used to compute set valued functions
# of the form:
#
#     F(x) = F'(x) U U{F(y) | x R y}
#
# This is used to compute the values of Read() sets as well as FOLLOW sets
# in LALR(1) generation.
#
# Inputs:  X    - An input set
#          R    - A relation
#          FP   - Set-valued function
# ------------------------------------------------------------------------------

def digraph(X, R, FP):
    N = {}
    for x in X:
        N[x] = 0
    stack = []
    F = {}
    for x in X:
        if N[x] == 0:
            traverse(x, N, stack, F, X, R, FP)
    return F

def traverse(x, N, stack, F, X, R, FP):
    stack.append(x)
    d = len(stack)
    N[x] = d
    F[x] = FP(x)             # F(X) <- F'(x)

    rel = R(x)               # Get y's related to x
    for y in rel:
        if N[y] == 0:
            traverse(y, N, stack, F, X, R, FP)
        N[x] = min(N[x], N[y])
        for a in F.get(y, []):
            if a not in F[x]:
                F[x].append(a)
    if N[x] == d:
        N[stack[-1]] = MAXINT
        F[stack[-1]] = F[x]
        element = stack.pop()
        while element != x:
            N[stack[-1]] = MAXINT
            F[stack[-1]] = F[x]
            element = stack.pop()

class LALRError(YaccError):
    pass


# -----------------------------------------------------------------------------
#                             == LRTable ==
#
# This class implements the LR table generation algorithm.  There are no
# public methods.
# -----------------------------------------------------------------------------

class LRTable:
    def __init__(self, grammar, log=None):
        self.grammar = grammar

        # Set up the logger
        if not log:
            log = NullLogger()
        self.log = log

        # Internal attributes
        self.lr_action     = {}        # Action table
        self.lr_goto       = {}        # Goto table
        self.lr_productions  = grammar.Productions    # Copy of grammar Production array
        self.lr_goto_cache = {}        # Cache of computed gotos
        self.lr0_cidhash   = {}        # Cache of closures

        self._add_count    = 0         # Internal counter used to detect cycles

        # Diagnostic information filled in by the table generator
        self.sr_conflict   = 0
        self.rr_conflict   = 0
        self.conflicts     = []        # List of conflicts

        self.sr_conflicts  = []
        self.rr_conflicts  = []

        # Build the tables
        self.grammar.build_lritems()
        self.grammar.compute_first()
        self.grammar.compute_follow()
        self.lr_parse_table()

    # Bind all production function names to callable objects in pdict
    def bind_callables(self, pdict):
        for p in self.lr_productions:
            p.bind(pdict)

    # Compute the LR(0) closure operation on I, where I is a set of LR(0) items.

    def lr0_closure(self, I):
        self._add_count += 1

        # Add everything in I to J
        J = I[:]
        didadd = True
        while didadd:
            didadd = False
            for j in J:
                for x in j.lr_after:
                    if getattr(x, 'lr0_added', 0) == self._add_count:
                        continue
                    # Add B --> .G to J
                    J.append(x.lr_next)
                    x.lr0_added = self._add_count
                    didadd = True

        return J

    # Compute the LR(0) goto function goto(I,X) where I is a set
    # of LR(0) items and X is a grammar symbol.   This function is written
    # in a way that guarantees uniqueness of the generated goto sets
    # (i.e. the same goto set will never be returned as two different Python
    # objects).  With uniqueness, we can later do fast set comparisons using
    # id(obj) instead of element-wise comparison.

    def lr0_goto(self, I, x):
        # First we look for a previously cached entry
        g = self.lr_goto_cache.get((id(I), x))
        if g:
            return g

        # Now we generate the goto set in a way that guarantees uniqueness
        # of the result

        s = self.lr_goto_cache.get(x)
        if not s:
            s = {}
            self.lr_goto_cache[x] = s

        gs = []
        for p in I:
            n = p.lr_next
            if n and n.lr_before == x:
                s1 = s.get(id(n))
                if not s1:
                    s1 = {}
                    s[id(n)] = s1
                gs.append(n)
                s = s1
        g = s.get('$end')
        if not g:
            if gs:
                g = self.lr0_closure(gs)
                s['$end'] = g
            else:
                s['$end'] = gs
        self.lr_goto_cache[(id(I), x)] = g
        return g

    # Compute the LR(0) sets of item function
    def lr0_items(self):
        C = [self.lr0_closure([self.grammar.Productions[0].lr_next])]
        i = 0
        for I in C:
            self.lr0_cidhash[id(I)] = i
            i += 1

        # Loop over the items in C and each grammar symbols
        i = 0
        while i < len(C):
            I = C[i]
            i += 1

            # Collect all of the symbols that could possibly be in the goto(I,X) sets
            asyms = {}
            for ii in I:
                for s in ii.usyms:
                    asyms[s] = None

            for x in asyms:
                g = self.lr0_goto(I, x)
                if not g or id(g) in self.lr0_cidhash:
                    continue
                self.lr0_cidhash[id(g)] = len(C)
                C.append(g)

        return C

    # -----------------------------------------------------------------------------
    #                       ==== LALR(1) Parsing ====
    #
    # LALR(1) parsing is almost exactly the same as SLR except that instead of
    # relying upon Follow() sets when performing reductions, a more selective
    # lookahead set that incorporates the state of the LR(0) machine is utilized.
    # Thus, we mainly just have to focus on calculating the lookahead sets.
    #
    # The method used here is due to DeRemer and Pennelo (1982).
    #
    # DeRemer, F. L., and T. J. Pennelo: "Efficient Computation of LALR(1)
    #     Lookahead Sets", ACM Transactions on Programming Languages and Systems,
    #     Vol. 4, No. 4, Oct. 1982, pp. 615-649
    #
    # Further details can also be found in:
    #
    #  J. Tremblay and P. Sorenson, "The Theory and Practice of Compiler Writing",
    #      McGraw-Hill Book Company, (1985).
    #
    # -----------------------------------------------------------------------------

    # -----------------------------------------------------------------------------
    # compute_nullable_nonterminals()
    #
    # Creates a dictionary containing all of the non-terminals that might produce
    # an empty production.
    # -----------------------------------------------------------------------------

    def compute_nullable_nonterminals(self):
        nullable = set()
        num_nullable = 0
        while True:
            for p in self.grammar.Productions[1:]:
                if p.len == 0:
                    nullable.add(p.name)
                    continue
                for t in p.prod:
                    if t not in nullable:
                        break
                else:
                    nullable.add(p.name)
            if len(nullable) == num_nullable:
                break
            num_nullable = len(nullable)
        return nullable

    # -----------------------------------------------------------------------------
    # find_nonterminal_trans(C)
    #
    # Given a set of LR(0) items, this functions finds all of the non-terminal
    # transitions.    These are transitions in which a dot appears immediately before
    # a non-terminal.   Returns a list of tuples of the form (state,N) where state
    # is the state number and N is the nonterminal symbol.
    #
    # The input C is the set of LR(0) items.
    # -----------------------------------------------------------------------------

    def find_nonterminal_transitions(self, C):
        trans = []
        for stateno, state in enumerate(C):
            for p in state:
                if p.lr_index < p.len - 1:
                    t = (stateno, p.prod[p.lr_index+1])
                    if t[1] in self.grammar.Nonterminals:
                        if t not in trans:
                            trans.append(t)
        return trans

    # -----------------------------------------------------------------------------
    # dr_relation()
    #
    # Computes the DR(p,A) relationships for non-terminal transitions.  The input
    # is a tuple (state,N) where state is a number and N is a nonterminal symbol.
    #
    # Returns a list of terminals.
    # -----------------------------------------------------------------------------

    def dr_relation(self, C, trans, nullable):
        state, N = trans
        terms = []

        g = self.lr0_goto(C[state], N)
        for p in g:
            if p.lr_index < p.len - 1:
                a = p.prod[p.lr_index+1]
                if a in self.grammar.Terminals:
                    if a not in terms:
                        terms.append(a)

        # This extra bit is to handle the start state
        if state == 0 and N == self.grammar.Productions[0].prod[0]:
            terms.append('$end')

        return terms

    # -----------------------------------------------------------------------------
    # reads_relation()
    #
    # Computes the READS() relation (p,A) READS (t,C).
    # -----------------------------------------------------------------------------

    def reads_relation(self, C, trans, empty):
        # Look for empty transitions
        rel = []
        state, N = trans

        g = self.lr0_goto(C[state], N)
        j = self.lr0_cidhash.get(id(g), -1)
        for p in g:
            if p.lr_index < p.len - 1:
                a = p.prod[p.lr_index + 1]
                if a in empty:
                    rel.append((j, a))

        return rel

    # -----------------------------------------------------------------------------
    # compute_lookback_includes()
    #
    # Determines the lookback and includes relations
    #
    # LOOKBACK:
    #
    # This relation is determined by running the LR(0) state machine forward.
    # For example, starting with a production "N : . A B C", we run it forward
    # to obtain "N : A B C ."   We then build a relationship between this final
    # state and the starting state.   These relationships are stored in a dictionary
    # lookdict.
    #
    # INCLUDES:
    #
    # Computes the INCLUDE() relation (p,A) INCLUDES (p',B).
    #
    # This relation is used to determine non-terminal transitions that occur
    # inside of other non-terminal transition states.   (p,A) INCLUDES (p', B)
    # if the following holds:
    #
    #       B -> LAT, where T -> epsilon and p' -L-> p
    #
    # L is essentially a prefix (which may be empty), T is a suffix that must be
    # able to derive an empty string.  State p' must lead to state p with the string L.
    #
    # -----------------------------------------------------------------------------

    def compute_lookback_includes(self, C, trans, nullable):
        lookdict = {}          # Dictionary of lookback relations
        includedict = {}       # Dictionary of include relations

        # Make a dictionary of non-terminal transitions
        dtrans = {}
        for t in trans:
            dtrans[t] = 1

        # Loop over all transitions and compute lookbacks and includes
        for state, N in trans:
            lookb = []
            includes = []
            for p in C[state]:
                if p.name != N:
                    continue

                # Okay, we have a name match.  We now follow the production all the way
                # through the state machine until we get the . on the right hand side

                lr_index = p.lr_index
                j = state
                while lr_index < p.len - 1:
                    lr_index = lr_index + 1
                    t = p.prod[lr_index]

                    # Check to see if this symbol and state are a non-terminal transition
                    if (j, t) in dtrans:
                        # Yes.  Okay, there is some chance that this is an includes relation
                        # the only way to know for certain is whether the rest of the
                        # production derives empty

                        li = lr_index + 1
                        while li < p.len:
                            if p.prod[li] in self.grammar.Terminals:
                                break      # No forget it
                            if p.prod[li] not in nullable:
                                break
                            li = li + 1
                        else:
                            # Appears to be a relation between (j,t) and (state,N)
                            includes.append((j, t))

                    g = self.lr0_goto(C[j], t)               # Go to next set
                    j = self.lr0_cidhash.get(id(g), -1)      # Go to next state

                # When we get here, j is the final state, now we have to locate the production
                for r in C[j]:
                    if r.name != p.name:
                        continue
                    if r.len != p.len:
                        continue
                    i = 0
                    # This look is comparing a production ". A B C" with "A B C ."
                    while i < r.lr_index:
                        if r.prod[i] != p.prod[i+1]:
                            break
                        i = i + 1
                    else:
                        lookb.append((j, r))
            for i in includes:
                if i not in includedict:
                    includedict[i] = []
                includedict[i].append((state, N))
            lookdict[(state, N)] = lookb

        return lookdict, includedict

    # -----------------------------------------------------------------------------
    # compute_read_sets()
    #
    # Given a set of LR(0) items, this function computes the read sets.
    #
    # Inputs:  C        =  Set of LR(0) items
    #          ntrans   = Set of nonterminal transitions
    #          nullable = Set of empty transitions
    #
    # Returns a set containing the read sets
    # -----------------------------------------------------------------------------

    def compute_read_sets(self, C, ntrans, nullable):
        FP = lambda x: self.dr_relation(C, x, nullable)
        R =  lambda x: self.reads_relation(C, x, nullable)
        F = digraph(ntrans, R, FP)
        return F

    # -----------------------------------------------------------------------------
    # compute_follow_sets()
    #
    # Given a set of LR(0) items, a set of non-terminal transitions, a readset,
    # and an include set, this function computes the follow sets
    #
    # Follow(p,A) = Read(p,A) U U {Follow(p',B) | (p,A) INCLUDES (p',B)}
    #
    # Inputs:
    #            ntrans     = Set of nonterminal transitions
    #            readsets   = Readset (previously computed)
    #            inclsets   = Include sets (previously computed)
    #
    # Returns a set containing the follow sets
    # -----------------------------------------------------------------------------

    def compute_follow_sets(self, ntrans, readsets, inclsets):
        FP = lambda x: readsets[x]
        R  = lambda x: inclsets.get(x, [])
        F = digraph(ntrans, R, FP)
        return F

    # -----------------------------------------------------------------------------
    # add_lookaheads()
    #
    # Attaches the lookahead symbols to grammar rules.
    #
    # Inputs:    lookbacks         -  Set of lookback relations
    #            followset         -  Computed follow set
    #
    # This function directly attaches the lookaheads to productions contained
    # in the lookbacks set
    # -----------------------------------------------------------------------------

    def add_lookaheads(self, lookbacks, followset):
        for trans, lb in lookbacks.items():
            # Loop over productions in lookback
            for state, p in lb:
                if state not in p.lookaheads:
                    p.lookaheads[state] = []
                f = followset.get(trans, [])
                for a in f:
                    if a not in p.lookaheads[state]:
                        p.lookaheads[state].append(a)

    # -----------------------------------------------------------------------------
    # add_lalr_lookaheads()
    #
    # This function does all of the work of adding lookahead information for use
    # with LALR parsing
    # -----------------------------------------------------------------------------

    def add_lalr_lookaheads(self, C):
        # Determine all of the nullable nonterminals
        nullable = self.compute_nullable_nonterminals()

        # Find all non-terminal transitions
        trans = self.find_nonterminal_transitions(C)

        # Compute read sets
        readsets = self.compute_read_sets(C, trans, nullable)

        # Compute lookback/includes relations
        lookd, included = self.compute_lookback_includes(C, trans, nullable)

        # Compute LALR FOLLOW sets
        followsets = self.compute_follow_sets(trans, readsets, included)

        # Add all of the lookaheads
        self.add_lookaheads(lookd, followsets)

    # -----------------------------------------------------------------------------
    # lr_parse_table()
    #
    # This function constructs the parse tables for SLR or LALR
    # -----------------------------------------------------------------------------
    def lr_parse_table(self):
        Productions = self.grammar.Productions
        Precedence  = self.grammar.Precedence
        goto   = self.lr_goto         # Goto array
        action = self.lr_action       # Action array
        log    = self.log             # Logger for output

        actionp = {}                  # Action production array (temporary)

        # Step 1: Construct C = { I0, I1, ... IN}, collection of LR(0) items
        # This determines the number of states

        C = self.lr0_items()
        self.add_lalr_lookaheads(C)

        # Build the parser table, state by state
        st = 0
        for I in C:
            # Loop over each production in I
            actlist = []              # List of actions
            st_action  = {}
            st_actionp = {}
            st_goto    = {}
            log.info('')
            log.info('state %d', st)
            log.info('')
            for p in I:
                log.info('    (%d) %s', p.number, p)
            log.info('')

            for p in I:
                    if p.len == p.lr_index + 1:
                        if p.name == "S'":
                            # Start symbol. Accept!
                            st_action['$end'] = 0
                            st_actionp['$end'] = p
                        else:
                            # We are at the end of a production.  Reduce!
                            laheads = p.lookaheads[st]
                            for a in laheads:
                                actlist.append((a, p, 'reduce using rule %d (%s)' % (p.number, p)))
                                r = st_action.get(a)
                                if r is not None:
                                    # Whoa. Have a shift/reduce or reduce/reduce conflict
                                    if r > 0:
                                        # Need to decide on shift or reduce here
                                        # By default we favor shifting. Need to add
                                        # some precedence rules here.

                                        # Shift precedence comes from the token
                                        sprec, slevel = Precedence.get(a, ('right', 0))

                                        # Reduce precedence comes from rule being reduced (p)
                                        rprec, rlevel = Productions[p.number].prec

                                        if (slevel < rlevel) or ((slevel == rlevel) and (rprec == 'left')):
                                            # We really need to reduce here.
                                            st_action[a] = -p.number
                                            st_actionp[a] = p
                                            if not slevel and not rlevel:
                                                log.info('  ! shift/reduce conflict for %s resolved as reduce', a)
                                                self.sr_conflicts.append((st, a, 'reduce'))
                                            Productions[p.number].reduced += 1
                                        elif (slevel == rlevel) and (rprec == 'nonassoc'):
                                            st_action[a] = None
                                        else:
                                            # Hmmm. Guess we'll keep the shift
                                            if not rlevel:
                                                log.info('  ! shift/reduce conflict for %s resolved as shift', a)
                                                self.sr_conflicts.append((st, a, 'shift'))
                                    elif r < 0:
                                        # Reduce/reduce conflict.   In this case, we favor the rule
                                        # that was defined first in the grammar file
                                        oldp = Productions[-r]
                                        pp = Productions[p.number]
                                        if oldp.line > pp.line:
                                            st_action[a] = -p.number
                                            st_actionp[a] = p
                                            chosenp, rejectp = pp, oldp
                                            Productions[p.number].reduced += 1
                                            Productions[oldp.number].reduced -= 1
                                        else:
                                            chosenp, rejectp = oldp, pp
                                        self.rr_conflicts.append((st, chosenp, rejectp))
                                        log.info('  ! reduce/reduce conflict for %s resolved using rule %d (%s)',
                                                 a, st_actionp[a].number, st_actionp[a])
                                    else:
                                        raise LALRError('Unknown conflict in state %d' % st)
                                else:
                                    st_action[a] = -p.number
                                    st_actionp[a] = p
                                    Productions[p.number].reduced += 1
                    else:
                        i = p.lr_index
                        a = p.prod[i+1]       # Get symbol right after the "."
                        if a in self.grammar.Terminals:
                            g = self.lr0_goto(I, a)
                            j = self.lr0_cidhash.get(id(g), -1)
                            if j >= 0:
                                # We are in a shift state
                                actlist.append((a, p, 'shift and go to state %d' % j))
                                r = st_action.get(a)
                                if r is not None:
                                    # Whoa have a shift/reduce or shift/shift conflict
                                    if r > 0:
                                        if r != j:
                                            raise LALRError('Shift/shift conflict in state %d' % st)
                                    elif r < 0:
                                        # Do a precedence check.
                                        #   -  if precedence of reduce rule is higher, we reduce.
                                        #   -  if precedence of reduce is same and left assoc, we reduce.
                                        #   -  otherwise we shift

                                        # Shift precedence comes from the token
                                        sprec, slevel = Precedence.get(a, ('right', 0))

                                        # Reduce precedence comes from the rule that could have been reduced
                                        rprec, rlevel = Productions[st_actionp[a].number].prec

                                        if (slevel > rlevel) or ((slevel == rlevel) and (rprec == 'right')):
                                            # We decide to shift here... highest precedence to shift
                                            Productions[st_actionp[a].number].reduced -= 1
                                            st_action[a] = j
                                            st_actionp[a] = p
                                            if not rlevel:
                                                log.info('  ! shift/reduce conflict for %s resolved as shift', a)
                                                self.sr_conflicts.append((st, a, 'shift'))
                                        elif (slevel == rlevel) and (rprec == 'nonassoc'):
                                            st_action[a] = None
                                        else:
                                            # Hmmm. Guess we'll keep the reduce
                                            if not slevel and not rlevel:
                                                log.info('  ! shift/reduce conflict for %s resolved as reduce', a)
                                                self.sr_conflicts.append((st, a, 'reduce'))

                                    else:
                                        raise LALRError('Unknown conflict in state %d' % st)
                                else:
                                    st_action[a] = j
                                    st_actionp[a] = p

            # Print the actions associated with each terminal
            _actprint = {}
            for a, p, m in actlist:
                if a in st_action:
                    if p is st_actionp[a]:
                        log.info('    %-15s %s', a, m)
                        _actprint[(a, m)] = 1
            log.info('')
            # Print the actions that were not used. (debugging)
            not_used = 0
            for a, p, m in actlist:
                if a in st_action:
                    if p is not st_actionp[a]:
                        if not (a, m) in _actprint:
                            log.debug('  ! %-15s [ %s ]', a, m)
                            not_used = 1
                            _actprint[(a, m)] = 1
            if not_used:
                log.debug('')

            # Construct the goto table for this state

            nkeys = {}
            for ii in I:
                for s in ii.usyms:
                    if s in self.grammar.Nonterminals:
                        nkeys[s] = None
            for n in nkeys:
                g = self.lr0_goto(I, n)
                j = self.lr0_cidhash.get(id(g), -1)
                if j >= 0:
                    st_goto[n] = j
                    log.info('    %-30s shift and go to state %d', n, j)

            action[st] = st_action
            actionp[st] = st_actionp
            goto[st] = st_goto
            st += 1

# -----------------------------------------------------------------------------
#                            === INTROSPECTION ===
#
# The following functions and classes are used to implement the PLY
# introspection features followed by the yacc() function itself.
# -----------------------------------------------------------------------------

# -----------------------------------------------------------------------------
# get_caller_module_dict()
#
# This function returns a dictionary containing all of the symbols defined within
# a caller further down the call stack.  This is used to get the environment
# associated with the yacc() call if none was provided.
# -----------------------------------------------------------------------------

def get_caller_module_dict(levels):
    f = sys._getframe(levels)
    ldict = f.f_globals.copy()
    if f.f_globals != f.f_locals:
        ldict.update(f.f_locals)
    return ldict

# -----------------------------------------------------------------------------
# parse_grammar()
#
# This takes a raw grammar rule string and parses it into production data
# -----------------------------------------------------------------------------
def parse_grammar(doc, file, line):
    grammar = []
    # Split the doc string into lines
    pstrings = doc.splitlines()
    lastp = None
    dline = line
    for ps in pstrings:
        dline += 1
        p = ps.split()
        if not p:
            continue
        try:
            if p[0] == '|':
                # This is a continuation of a previous rule
                if not lastp:
                    raise SyntaxError("%s:%d: Misplaced '|'" % (file, dline))
                prodname = lastp
                syms = p[1:]
            else:
                prodname = p[0]
                lastp = prodname
                syms   = p[2:]
                assign = p[1]
                if assign != ':' and assign != '::=':
                    raise SyntaxError("%s:%d: Syntax error. Expected ':'" % (file, dline))

            grammar.append((file, dline, prodname, syms))
        except SyntaxError:
            raise
        except Exception:
            raise SyntaxError('%s:%d: Syntax error in rule %r' % (file, dline, ps.strip()))

    return grammar

# -----------------------------------------------------------------------------
# ParserReflect()
#
# This class represents information extracted for building a parser including
# start symbol, error function, tokens, precedence list, action functions,
# etc.
# -----------------------------------------------------------------------------
class ParserReflect(object):
    def __init__(self, pdict, log=None):
        self.pdict      = pdict
        self.start      = None
        self.error_func = None
        self.tokens     = None
        self.modules    = set()
        self.grammar    = []
        self.error      = False

        if log is None:
            self.log = PlyLogger(sys.stderr)
        else:
            self.log = log

    # Get all of the basic information
    def get_all(self):
        self.get_start()
        self.get_error_func()
        self.get_tokens()
        self.get_precedence()
        self.get_pfunctions()

    # Validate all of the information
    def validate_all(self):
        self.validate_start()
        self.validate_error_func()
        self.validate_tokens()
        self.validate_precedence()
        self.validate_pfunctions()
        self.validate_modules()
        return self.error

    # Compute a signature over the grammar
    def signature(self):
        parts = []
        try:
            if self.start:
                parts.append(self.start)
            if self.prec:
                parts.append(''.join([''.join(p) for p in self.prec]))
            if self.tokens:
                parts.append(' '.join(self.tokens))
            for f in self.pfuncs:
                if f[3]:
                    parts.append(f[3])
        except (TypeError, ValueError):
            pass
        return ''.join(parts)

    # -----------------------------------------------------------------------------
    # validate_modules()
    #
    # This method checks to see if there are duplicated p_rulename() functions
    # in the parser module file.  Without this function, it is really easy for
    # users to make mistakes by cutting and pasting code fragments (and it's a real
    # bugger to try and figure out why the resulting parser doesn't work).  Therefore,
    # we just do a little regular expression pattern matching of def statements
    # to try and detect duplicates.
    # -----------------------------------------------------------------------------

    def validate_modules(self):
        # Match def p_funcname(
        fre = re.compile(r'\s*def\s+(p_[a-zA-Z_0-9]*)\(')

        for module in self.modules:
            try:
                lines, linen = inspect.getsourcelines(module)
            except IOError:
                continue

            counthash = {}
            for linen, line in enumerate(lines):
                linen += 1
                m = fre.match(line)
                if m:
                    name = m.group(1)
                    prev = counthash.get(name)
                    if not prev:
                        counthash[name] = linen
                    else:
                        filename = inspect.getsourcefile(module)
                        self.log.warning('%s:%d: Function %s redefined. Previously defined on line %d',
                                         filename, linen, name, prev)

    # Get the start symbol
    def get_start(self):
        self.start = self.pdict.get('start')

    # Validate the start symbol
    def validate_start(self):
        if self.start is not None:
            if not isinstance(self.start, str):
                self.log.error("'start' must be a string")

    # Look for error handler
    def get_error_func(self):
        self.error_func = self.pdict.get('p_error')

    # Validate the error function
    def validate_error_func(self):
        if self.error_func:
            if isinstance(self.error_func, types.FunctionType):
                ismethod = 0
            elif isinstance(self.error_func, types.MethodType):
                ismethod = 1
            else:
                self.log.error("'p_error' defined, but is not a function or method")
                self.error = True
                return

            eline = self.error_func.__code__.co_firstlineno
            efile = self.error_func.__code__.co_filename
            module = inspect.getmodule(self.error_func)
            self.modules.add(module)

            argcount = self.error_func.__code__.co_argcount - ismethod
            if argcount != 1:
                self.log.error('%s:%d: p_error() requires 1 argument', efile, eline)
                self.error = True

    # Get the tokens map
    def get_tokens(self):
        tokens = self.pdict.get('tokens')
        if not tokens:
            self.log.error('No token list is defined')
            self.error = True
            return

        if not isinstance(tokens, (list, tuple)):
            self.log.error('tokens must be a list or tuple')
            self.error = True
            return

        if not tokens:
            self.log.error('tokens is empty')
            self.error = True
            return

        self.tokens = sorted(tokens)

    # Validate the tokens
    def validate_tokens(self):
        # Validate the tokens.
        if 'error' in self.tokens:
            self.log.error("Illegal token name 'error'. Is a reserved word")
            self.error = True
            return

        terminals = set()
        for n in self.tokens:
            if n in terminals:
                self.log.warning('Token %r multiply defined', n)
            terminals.add(n)

    # Get the precedence map (if any)
    def get_precedence(self):
        self.prec = self.pdict.get('precedence')

    # Validate and parse the precedence map
    def validate_precedence(self):
        preclist = []
        if self.prec:
            if not isinstance(self.prec, (list, tuple)):
                self.log.error('precedence must be a list or tuple')
                self.error = True
                return
            for level, p in enumerate(self.prec):
                if not isinstance(p, (list, tuple)):
                    self.log.error('Bad precedence table')
                    self.error = True
                    return

                if len(p) < 2:
                    self.log.error('Malformed precedence entry %s. Must be (assoc, term, ..., term)', p)
                    self.error = True
                    return
                assoc = p[0]
                if not isinstance(assoc, str):
                    self.log.error('precedence associativity must be a string')
                    self.error = True
                    return
                for term in p[1:]:
                    if not isinstance(term, str):
                        self.log.error('precedence items must be strings')
                        self.error = True
                        return
                    preclist.append((term, assoc, level+1))
        self.preclist = preclist

    # Get all p_functions from the grammar
    def get_pfunctions(self):
        p_functions = []
        for name, item in self.pdict.items():
            if not name.startswith('p_') or name == 'p_error':
                continue
            if isinstance(item, (types.FunctionType, types.MethodType)):
                line = getattr(item, 'co_firstlineno', item.__code__.co_firstlineno)
                module = inspect.getmodule(item)
                p_functions.append((line, module, name, item.__doc__))

        # Sort all of the actions by line number; make sure to stringify
        # modules to make them sortable, since `line` may not uniquely sort all
        # p functions
        p_functions.sort(key=lambda p_function: (
            p_function[0],
            str(p_function[1]),
            p_function[2],
            p_function[3]))
        self.pfuncs = p_functions

    # Validate all of the p_functions
    def validate_pfunctions(self):
        grammar = []
        # Check for non-empty symbols
        if len(self.pfuncs) == 0:
            self.log.error('no rules of the form p_rulename are defined')
            self.error = True
            return

        for line, module, name, doc in self.pfuncs:
            file = inspect.getsourcefile(module)
            func = self.pdict[name]
            if isinstance(func, types.MethodType):
                reqargs = 2
            else:
                reqargs = 1
            if func.__code__.co_argcount > reqargs:
                self.log.error('%s:%d: Rule %r has too many arguments', file, line, func.__name__)
                self.error = True
            elif func.__code__.co_argcount < reqargs:
                self.log.error('%s:%d: Rule %r requires an argument', file, line, func.__name__)
                self.error = True
            elif not func.__doc__:
                self.log.warning('%s:%d: No documentation string specified in function %r (ignored)',
                                 file, line, func.__name__)
            else:
                try:
                    parsed_g = parse_grammar(doc, file, line)
                    for g in parsed_g:
                        grammar.append((name, g))
                except SyntaxError as e:
                    self.log.error(str(e))
                    self.error = True

                # Looks like a valid grammar rule
                # Mark the file in which defined.
                self.modules.add(module)

        # Secondary validation step that looks for p_ definitions that are not functions
        # or functions that look like they might be grammar rules.

        for n, v in self.pdict.items():
            if n.startswith('p_') and isinstance(v, (types.FunctionType, types.MethodType)):
                continue
            if n.startswith('t_'):
                continue
            if n.startswith('p_') and n != 'p_error':
                self.log.warning('%r not defined as a function', n)
            if ((isinstance(v, types.FunctionType) and v.__code__.co_argcount == 1) or
                   (isinstance(v, types.MethodType) and v.__func__.__code__.co_argcount == 2)):
                if v.__doc__:
                    try:
                        doc = v.__doc__.split(' ')
                        if doc[1] == ':':
                            self.log.warning('%s:%d: Possible grammar rule %r defined without p_ prefix',
                                             v.__code__.co_filename, v.__code__.co_firstlineno, n)
                    except IndexError:
                        pass

        self.grammar = grammar

# -----------------------------------------------------------------------------
# yacc(module)
#
# Build a parser
# -----------------------------------------------------------------------------

def yacc(*, debug=yaccdebug, module=None, start=None,
         check_recursion=True, optimize=False, debugfile=debug_file,
         debuglog=None, errorlog=None):

    # Reference to the parsing method of the last built parser
    global parse

    if errorlog is None:
        errorlog = PlyLogger(sys.stderr)

    # Get the module dictionary used for the parser
    if module:
        _items = [(k, getattr(module, k)) for k in dir(module)]
        pdict = dict(_items)
        # If no __file__ or __package__ attributes are available, try to obtain them
        # from the __module__ instead
        if '__file__' not in pdict:
            pdict['__file__'] = sys.modules[pdict['__module__']].__file__
        if '__package__' not in pdict and '__module__' in pdict:
            if hasattr(sys.modules[pdict['__module__']], '__package__'):
                pdict['__package__'] = sys.modules[pdict['__module__']].__package__
    else:
        pdict = get_caller_module_dict(2)

    # Set start symbol if it's specified directly using an argument
    if start is not None:
        pdict['start'] = start

    # Collect parser information from the dictionary
    pinfo = ParserReflect(pdict, log=errorlog)
    pinfo.get_all()

    if pinfo.error:
        raise YaccError('Unable to build parser')

    if debuglog is None:
        if debug:
            try:
                debuglog = PlyLogger(open(debugfile, 'w'))
            except IOError as e:
                errorlog.warning("Couldn't open %r. %s" % (debugfile, e))
                debuglog = NullLogger()
        else:
            debuglog = NullLogger()

    debuglog.info('Created by PLY (http://www.dabeaz.com/ply)')

    errors = False

    # Validate the parser information
    if pinfo.validate_all():
        raise YaccError('Unable to build parser')

    if not pinfo.error_func:
        errorlog.warning('no p_error() function is defined')

    # Create a grammar object
    grammar = Grammar(pinfo.tokens)

    # Set precedence level for terminals
    for term, assoc, level in pinfo.preclist:
        try:
            grammar.set_precedence(term, assoc, level)
        except GrammarError as e:
            errorlog.warning('%s', e)

    # Add productions to the grammar
    for funcname, gram in pinfo.grammar:
        file, line, prodname, syms = gram
        try:
            grammar.add_production(prodname, syms, funcname, file, line)
        except GrammarError as e:
            errorlog.error('%s', e)
            errors = True

    # Set the grammar start symbols
    try:
        if start is None:
            grammar.set_start(pinfo.start)
        else:
            grammar.set_start(start)
    except GrammarError as e:
        errorlog.error(str(e))
        errors = True

    if errors:
        raise YaccError('Unable to build parser')

    # Verify the grammar structure
    undefined_symbols = grammar.undefined_symbols()
    for sym, prod in undefined_symbols:
        errorlog.error('%s:%d: Symbol %r used, but not defined as a token or a rule', prod.file, prod.line, sym)
        errors = True

    unused_terminals = grammar.unused_terminals()
    if unused_terminals:
        debuglog.info('')
        debuglog.info('Unused terminals:')
        debuglog.info('')
        for term in unused_terminals:
            errorlog.warning('Token %r defined, but not used', term)
            debuglog.info('    %s', term)

    # Print out all productions to the debug log
    if debug:
        debuglog.info('')
        debuglog.info('Grammar')
        debuglog.info('')
        for n, p in enumerate(grammar.Productions):
            debuglog.info('Rule %-5d %s', n, p)

    # Find unused non-terminals
    unused_rules = grammar.unused_rules()
    for prod in unused_rules:
        errorlog.warning('%s:%d: Rule %r defined, but not used', prod.file, prod.line, prod.name)

    if len(unused_terminals) == 1:
        errorlog.warning('There is 1 unused token')
    if len(unused_terminals) > 1:
        errorlog.warning('There are %d unused tokens', len(unused_terminals))

    if len(unused_rules) == 1:
        errorlog.warning('There is 1 unused rule')
    if len(unused_rules) > 1:
        errorlog.warning('There are %d unused rules', len(unused_rules))

    if debug:
        debuglog.info('')
        debuglog.info('Terminals, with rules where they appear')
        debuglog.info('')
        terms = list(grammar.Terminals)
        terms.sort()
        for term in terms:
            debuglog.info('%-20s : %s', term, ' '.join([str(s) for s in grammar.Terminals[term]]))

        debuglog.info('')
        debuglog.info('Nonterminals, with rules where they appear')
        debuglog.info('')
        nonterms = list(grammar.Nonterminals)
        nonterms.sort()
        for nonterm in nonterms:
            debuglog.info('%-20s : %s', nonterm, ' '.join([str(s) for s in grammar.Nonterminals[nonterm]]))
        debuglog.info('')

    if check_recursion:
        unreachable = grammar.find_unreachable()
        for u in unreachable:
            errorlog.warning('Symbol %r is unreachable', u)

        infinite = grammar.infinite_cycles()
        for inf in infinite:
            errorlog.error('Infinite recursion detected for symbol %r', inf)
            errors = True

    unused_prec = grammar.unused_precedence()
    for term, assoc in unused_prec:
        errorlog.error('Precedence rule %r defined for unknown symbol %r', assoc, term)
        errors = True

    if errors:
        raise YaccError('Unable to build parser')

    # Run the LRTable on the grammar
    lr = LRTable(grammar, debuglog)

    if debug:
        num_sr = len(lr.sr_conflicts)

        # Report shift/reduce and reduce/reduce conflicts
        if num_sr == 1:
            errorlog.warning('1 shift/reduce conflict')
        elif num_sr > 1:
            errorlog.warning('%d shift/reduce conflicts', num_sr)

        num_rr = len(lr.rr_conflicts)
        if num_rr == 1:
            errorlog.warning('1 reduce/reduce conflict')
        elif num_rr > 1:
            errorlog.warning('%d reduce/reduce conflicts', num_rr)

    # Write out conflicts to the output file
    if debug and (lr.sr_conflicts or lr.rr_conflicts):
        debuglog.warning('')
        debuglog.warning('Conflicts:')
        debuglog.warning('')

        for state, tok, resolution in lr.sr_conflicts:
            debuglog.warning('shift/reduce conflict for %s in state %d resolved as %s',  tok, state, resolution)

        already_reported = set()
        for state, rule, rejected in lr.rr_conflicts:
            if (state, id(rule), id(rejected)) in already_reported:
                continue
            debuglog.warning('reduce/reduce conflict in state %d resolved using rule (%s)', state, rule)
            debuglog.warning('rejected rule (%s) in state %d', rejected, state)
            errorlog.warning('reduce/reduce conflict in state %d resolved using rule (%s)', state, rule)
            errorlog.warning('rejected rule (%s) in state %d', rejected, state)
            already_reported.add((state, id(rule), id(rejected)))

        warned_never = []
        for state, rule, rejected in lr.rr_conflicts:
            if not rejected.reduced and (rejected not in warned_never):
                debuglog.warning('Rule (%s) is never reduced', rejected)
                errorlog.warning('Rule (%s) is never reduced', rejected)
                warned_never.append(rejected)

    # Build the parser
    lr.bind_callables(pinfo.pdict)
    parser = LRParser(lr, pinfo.error_func)

    parse = parser.parse
    return parser