1983 lines
77 KiB
Python
1983 lines
77 KiB
Python
# -----------------------------------------------------------------------------
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# sly: yacc.py
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#
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# Copyright (C) 2016
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# David M. Beazley (Dabeaz LLC)
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# All rights reserved.
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#
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# Redistribution and use in source and binary forms, with or without
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# modification, are permitted provided that the following conditions are
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# met:
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#
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# * Redistributions of source code must retain the above copyright notice,
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# this list of conditions and the following disclaimer.
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# * Redistributions in binary form must reproduce the above copyright notice,
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# this list of conditions and the following disclaimer in the documentation
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# and/or other materials provided with the distribution.
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# * Neither the name of the David Beazley or Dabeaz LLC may be used to
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# endorse or promote products derived from this software without
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# specific prior written permission.
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#
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# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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# A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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# OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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# -----------------------------------------------------------------------------
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import sys
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import inspect
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from collections import OrderedDict, defaultdict
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__version__ = '0.0'
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__all__ = [ 'Parser' ]
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class YaccError(Exception):
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'''
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Exception raised for yacc-related build errors.
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'''
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pass
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#-----------------------------------------------------------------------------
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# === User configurable parameters ===
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#
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# Change these to modify the default behavior of yacc (if you wish).
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# Move these parameters to the Yacc class itself.
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#-----------------------------------------------------------------------------
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ERROR_COUNT = 3 # Number of symbols that must be shifted to leave recovery mode
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MAXINT = sys.maxsize
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# This object is a stand-in for a logging object created by the
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# logging module. PLY will use this by default to create things
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# such as the parser.out file. If a user wants more detailed
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# information, they can create their own logging object and pass
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# it into PLY.
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class PlyLogger(object):
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def __init__(self, f):
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self.f = f
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def debug(self, msg, *args, **kwargs):
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self.f.write((msg % args) + '\n')
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info = debug
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def warning(self, msg, *args, **kwargs):
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self.f.write('WARNING: ' + (msg % args) + '\n')
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def error(self, msg, *args, **kwargs):
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self.f.write('ERROR: ' + (msg % args) + '\n')
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critical = debug
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# ----------------------------------------------------------------------
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# This class is used to hold non-terminal grammar symbols during parsing.
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# It normally has the following attributes set:
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# .type = Grammar symbol type
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# .value = Symbol value
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# .lineno = Starting line number
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# .index = Starting lex position
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# ----------------------------------------------------------------------
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class YaccSymbol:
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def __str__(self):
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return self.type
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def __repr__(self):
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return str(self)
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# ----------------------------------------------------------------------
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# This class is a wrapper around the objects actually passed to each
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# grammar rule. Index lookup and assignment actually assign the
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# .value attribute of the underlying YaccSymbol object.
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# The lineno() method returns the line number of a given
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# item (or 0 if not defined).
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# ----------------------------------------------------------------------
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class YaccProduction:
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def __init__(self, s, stack=None):
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self._slice = s
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self._namemap = { }
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self._stack = stack
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def __getitem__(self, n):
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if n >= 0:
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return self._slice[n].value
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else:
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return self._stack[n].value
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def __setitem__(self, n, v):
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if n >= 0:
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self._slice[n].value = v
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else:
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self._stack[n].value = v
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def __len__(self):
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return len(self._slice)
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@property
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def lineno(self):
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for tok in self._slice:
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lineno = getattr(tok, 'lineno', None)
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if lineno:
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return lineno
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raise AttributeError('No line number found')
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@property
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def index(self):
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for tok in self._slice:
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index = getattr(tok, 'index', None)
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if index:
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return index
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raise AttributeError('No index attribute found')
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def __getattr__(self, name):
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return self._slice[self._namemap[name]].value
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def __setattr__(self, name, value):
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if name[0:1] == '_' or name not in self._namemap:
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super().__setattr__(name, value)
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else:
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self._slice[self._namemap[name]].value = value
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# -----------------------------------------------------------------------------
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# === Grammar Representation ===
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#
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# The following functions, classes, and variables are used to represent and
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# manipulate the rules that make up a grammar.
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# -----------------------------------------------------------------------------
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# -----------------------------------------------------------------------------
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# class Production:
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#
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# This class stores the raw information about a single production or grammar rule.
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# A grammar rule refers to a specification such as this:
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#
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# expr : expr PLUS term
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#
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# Here are the basic attributes defined on all productions
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#
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# name - Name of the production. For example 'expr'
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# prod - A list of symbols on the right side ['expr','PLUS','term']
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# prec - Production precedence level
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# number - Production number.
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# func - Function that executes on reduce
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# file - File where production function is defined
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# lineno - Line number where production function is defined
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#
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# The following attributes are defined or optional.
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#
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# len - Length of the production (number of symbols on right hand side)
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# usyms - Set of unique symbols found in the production
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# -----------------------------------------------------------------------------
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class Production(object):
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reduced = 0
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def __init__(self, number, name, prod, precedence=('right', 0), func=None, file='', line=0):
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self.name = name
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self.prod = tuple(prod)
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self.number = number
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self.func = func
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self.file = file
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self.line = line
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self.prec = precedence
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# Internal settings used during table construction
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self.len = len(self.prod) # Length of the production
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# Create a list of unique production symbols used in the production
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self.usyms = []
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symmap = defaultdict(list)
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for n, s in enumerate(self.prod):
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symmap[s].append(n)
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if s not in self.usyms:
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self.usyms.append(s)
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# Create a dict mapping symbol names to indices
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m = {}
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for key, indices in symmap.items():
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if len(indices) == 1:
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m[key] = indices[0]
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else:
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for n, index in enumerate(indices):
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m[key+str(n)] = index
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self.namemap = m
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# List of all LR items for the production
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self.lr_items = []
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self.lr_next = None
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def __str__(self):
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if self.prod:
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s = '%s -> %s' % (self.name, ' '.join(self.prod))
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else:
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s = '%s -> <empty>' % self.name
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if self.prec[1]:
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s += ' [precedence=%s, level=%d]' % self.prec
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return s
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def __repr__(self):
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return 'Production(' + str(self) + ')'
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def __len__(self):
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return len(self.prod)
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def __nonzero__(self):
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raise RuntimeError('Used')
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return 1
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def __getitem__(self, index):
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return self.prod[index]
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# Return the nth lr_item from the production (or None if at the end)
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def lr_item(self, n):
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if n > len(self.prod):
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return None
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p = LRItem(self, n)
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# Precompute the list of productions immediately following.
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try:
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p.lr_after = Prodnames[p.prod[n+1]]
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except (IndexError, KeyError):
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p.lr_after = []
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try:
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p.lr_before = p.prod[n-1]
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except IndexError:
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p.lr_before = None
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return p
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# -----------------------------------------------------------------------------
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# class LRItem
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#
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# This class represents a specific stage of parsing a production rule. For
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# example:
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#
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# expr : expr . PLUS term
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#
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# In the above, the "." represents the current location of the parse. Here
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# basic attributes:
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#
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# name - Name of the production. For example 'expr'
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# prod - A list of symbols on the right side ['expr','.', 'PLUS','term']
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# number - Production number.
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#
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# lr_next Next LR item. Example, if we are ' expr -> expr . PLUS term'
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# then lr_next refers to 'expr -> expr PLUS . term'
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# lr_index - LR item index (location of the ".") in the prod list.
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# lookaheads - LALR lookahead symbols for this item
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# len - Length of the production (number of symbols on right hand side)
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# lr_after - List of all productions that immediately follow
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# lr_before - Grammar symbol immediately before
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# -----------------------------------------------------------------------------
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class LRItem(object):
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def __init__(self, p, n):
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self.name = p.name
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self.prod = list(p.prod)
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self.number = p.number
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self.lr_index = n
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self.lookaheads = {}
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self.prod.insert(n, '.')
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self.prod = tuple(self.prod)
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self.len = len(self.prod)
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self.usyms = p.usyms
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def __str__(self):
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if self.prod:
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s = '%s -> %s' % (self.name, ' '.join(self.prod))
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else:
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s = '%s -> <empty>' % self.name
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return s
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def __repr__(self):
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return 'LRItem(' + str(self) + ')'
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# -----------------------------------------------------------------------------
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# rightmost_terminal()
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#
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# Return the rightmost terminal from a list of symbols. Used in add_production()
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# -----------------------------------------------------------------------------
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def rightmost_terminal(symbols, terminals):
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i = len(symbols) - 1
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while i >= 0:
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if symbols[i] in terminals:
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return symbols[i]
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i -= 1
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return None
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# -----------------------------------------------------------------------------
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# === GRAMMAR CLASS ===
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#
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# The following class represents the contents of the specified grammar along
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# with various computed properties such as first sets, follow sets, LR items, etc.
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# This data is used for critical parts of the table generation process later.
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# -----------------------------------------------------------------------------
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class GrammarError(YaccError):
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pass
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class Grammar(object):
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def __init__(self, terminals):
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self.Productions = [None] # A list of all of the productions. The first
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# entry is always reserved for the purpose of
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# building an augmented grammar
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self.Prodnames = {} # A dictionary mapping the names of nonterminals to a list of all
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# productions of that nonterminal.
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self.Prodmap = {} # A dictionary that is only used to detect duplicate
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# productions.
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self.Terminals = {} # A dictionary mapping the names of terminal symbols to a
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# list of the rules where they are used.
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for term in terminals:
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self.Terminals[term] = []
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self.Terminals['error'] = []
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self.Nonterminals = {} # A dictionary mapping names of nonterminals to a list
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# of rule numbers where they are used.
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self.First = {} # A dictionary of precomputed FIRST(x) symbols
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self.Follow = {} # A dictionary of precomputed FOLLOW(x) symbols
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self.Precedence = {} # Precedence rules for each terminal. Contains tuples of the
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# form ('right',level) or ('nonassoc', level) or ('left',level)
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self.UsedPrecedence = set() # Precedence rules that were actually used by the grammer.
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# This is only used to provide error checking and to generate
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# a warning about unused precedence rules.
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self.Start = None # Starting symbol for the grammar
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def __len__(self):
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return len(self.Productions)
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def __getitem__(self, index):
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return self.Productions[index]
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# -----------------------------------------------------------------------------
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# set_precedence()
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#
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# Sets the precedence for a given terminal. assoc is the associativity such as
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# 'left','right', or 'nonassoc'. level is a numeric level.
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#
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# -----------------------------------------------------------------------------
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def set_precedence(self, term, assoc, level):
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assert self.Productions == [None], 'Must call set_precedence() before add_production()'
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if term in self.Precedence:
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raise GrammarError('Precedence already specified for terminal %r' % term)
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if assoc not in ['left', 'right', 'nonassoc']:
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raise GrammarError("Associativity must be one of 'left','right', or 'nonassoc'")
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self.Precedence[term] = (assoc, level)
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# -----------------------------------------------------------------------------
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# add_production()
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#
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# Given an action function, this function assembles a production rule and
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# computes its precedence level.
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#
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# The production rule is supplied as a list of symbols. For example,
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# a rule such as 'expr : expr PLUS term' has a production name of 'expr' and
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# symbols ['expr','PLUS','term'].
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#
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# Precedence is determined by the precedence of the right-most non-terminal
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# or the precedence of a terminal specified by %prec.
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#
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# A variety of error checks are performed to make sure production symbols
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# are valid and that %prec is used correctly.
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# -----------------------------------------------------------------------------
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def add_production(self, prodname, syms, func=None, file='', line=0):
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if prodname in self.Terminals:
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raise GrammarError('%s:%d: Illegal rule name %r. Already defined as a token' % (file, line, prodname))
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if prodname == 'error':
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raise GrammarError('%s:%d: Illegal rule name %r. error is a reserved word' % (file, line, prodname))
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# Look for literal tokens
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for n, s in enumerate(syms):
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if s[0] in "'\"" and s[0] == s[-1]:
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c = s[1:-1]
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if (len(c) != 1):
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raise GrammarError('%s:%d: Literal token %s in rule %r may only be a single character' %
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(file, line, s, prodname))
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if c not in self.Terminals:
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self.Terminals[c] = []
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syms[n] = c
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continue
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# Determine the precedence level
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if '%prec' in syms:
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if syms[-1] == '%prec':
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raise GrammarError('%s:%d: Syntax error. Nothing follows %%prec' % (file, line))
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if syms[-2] != '%prec':
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raise GrammarError('%s:%d: Syntax error. %%prec can only appear at the end of a grammar rule' %
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(file, line))
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precname = syms[-1]
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prodprec = self.Precedence.get(precname)
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if not prodprec:
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raise GrammarError('%s:%d: Nothing known about the precedence of %r' % (file, line, precname))
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else:
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self.UsedPrecedence.add(precname)
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del syms[-2:] # Drop %prec from the rule
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else:
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# If no %prec, precedence is determined by the rightmost terminal symbol
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precname = rightmost_terminal(syms, self.Terminals)
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prodprec = self.Precedence.get(precname, ('right', 0))
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# See if the rule is already in the rulemap
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map = '%s -> %s' % (prodname, syms)
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if map in self.Prodmap:
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m = self.Prodmap[map]
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raise GrammarError('%s:%d: Duplicate rule %s. ' % (file, line, m) +
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'Previous definition at %s:%d' % (m.file, m.line))
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# From this point on, everything is valid. Create a new Production instance
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pnumber = len(self.Productions)
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if prodname not in self.Nonterminals:
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self.Nonterminals[prodname] = []
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# Add the production number to Terminals and Nonterminals
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for t in syms:
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if t in self.Terminals:
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self.Terminals[t].append(pnumber)
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else:
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if t not in self.Nonterminals:
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self.Nonterminals[t] = []
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self.Nonterminals[t].append(pnumber)
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# Create a production and add it to the list of productions
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p = Production(pnumber, prodname, syms, prodprec, func, file, line)
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self.Productions.append(p)
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self.Prodmap[map] = p
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# Add to the global productions list
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try:
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self.Prodnames[prodname].append(p)
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except KeyError:
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self.Prodnames[prodname] = [p]
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# -----------------------------------------------------------------------------
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# set_start()
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#
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# Sets the starting symbol and creates the augmented grammar. Production
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# rule 0 is S' -> start where start is the start symbol.
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# -----------------------------------------------------------------------------
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def set_start(self, start=None):
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if not start:
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start = self.Productions[1].name
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if start not in self.Nonterminals:
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raise GrammarError('start symbol %s undefined' % start)
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self.Productions[0] = Production(0, "S'", [start])
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self.Nonterminals[start].append(0)
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self.Start = start
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# -----------------------------------------------------------------------------
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# find_unreachable()
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#
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# Find all of the nonterminal symbols that can't be reached from the starting
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# symbol. Returns a list of nonterminals that can't be reached.
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# -----------------------------------------------------------------------------
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def find_unreachable(self):
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# Mark all symbols that are reachable from a symbol s
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def mark_reachable_from(s):
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if s in reachable:
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return
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reachable.add(s)
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for p in self.Prodnames.get(s, []):
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for r in p.prod:
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mark_reachable_from(r)
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reachable = set()
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mark_reachable_from(self.Productions[0].prod[0])
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return [s for s in self.Nonterminals if s not in reachable]
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# -----------------------------------------------------------------------------
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# infinite_cycles()
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#
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# This function looks at the various parsing rules and tries to detect
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# infinite recursion cycles (grammar rules where there is no possible way
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# to derive a string of only terminals).
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# -----------------------------------------------------------------------------
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def infinite_cycles(self):
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terminates = {}
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# Terminals:
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for t in self.Terminals:
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terminates[t] = True
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terminates['$end'] = True
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# Nonterminals:
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|
# 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
|
|
|
|
|
|
# ----------------------------------------------------------------------
|
|
# Debugging output. Printing the grammar will produce a detailed
|
|
# description along with some diagnostics.
|
|
# ----------------------------------------------------------------------
|
|
def __str__(self):
|
|
out = []
|
|
out.append('Grammar:\n')
|
|
for n, p in enumerate(self.Productions):
|
|
out.append('Rule %-5d %s' % (n, p))
|
|
|
|
unused_terminals = self.unused_terminals()
|
|
if unused_terminals:
|
|
out.append('\nUnused terminals:\n')
|
|
for term in unused_terminals:
|
|
out.append(' %s' % term)
|
|
|
|
out.append('\nTerminals, with rules where they appear:\n')
|
|
for term in sorted(self.Terminals):
|
|
out.append('%-20s : %s' % (term, ' '.join(str(s) for s in self.Terminals[term])))
|
|
|
|
out.append('\nNonterminals, with rules where they appear:\n')
|
|
for nonterm in sorted(self.Nonterminals):
|
|
out.append('%-20s : %s' % (nonterm, ' '.join(str(s) for s in self.Nonterminals[nonterm])))
|
|
|
|
out.append('')
|
|
return '\n'.join(out)
|
|
|
|
# -----------------------------------------------------------------------------
|
|
# === 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
|
|
|
|
# -----------------------------------------------------------------------------
|
|
# == LRGeneratedTable ==
|
|
#
|
|
# This class implements the LR table generation algorithm. There are no
|
|
# public methods except for write()
|
|
# -----------------------------------------------------------------------------
|
|
|
|
class LRTable(object):
|
|
def __init__(self, grammar):
|
|
self.grammar = grammar
|
|
|
|
# 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
|
|
|
|
# Diagonistic information filled in by the table generator
|
|
self.state_descriptions = OrderedDict()
|
|
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()
|
|
|
|
# Build default states
|
|
# This 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
|
|
self.defaulted_states = {}
|
|
for state, actions in self.lr_action.items():
|
|
rules = list(actions.values())
|
|
if len(rules) == 1 and rules[0] < 0:
|
|
self.defaulted_states[state] = rules[0]
|
|
|
|
# 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):
|
|
dr_set = {}
|
|
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 final LALR parse table. Touch this code and die.
|
|
# -----------------------------------------------------------------------------
|
|
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
|
|
|
|
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
|
|
for st, I in enumerate(C):
|
|
descrip = []
|
|
# Loop over each production in I
|
|
actlist = [] # List of actions
|
|
st_action = {}
|
|
st_actionp = {}
|
|
st_goto = {}
|
|
|
|
descrip.append('\nstate %d\n' % st)
|
|
for p in I:
|
|
descrip.append(' (%d) %s' % (p.number, p))
|
|
|
|
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:
|
|
# 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.
|
|
sprec, slevel = Productions[st_actionp[a].number].prec
|
|
rprec, rlevel = Precedence.get(a, ('right', 0))
|
|
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:
|
|
descrip.append(' ! 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:
|
|
descrip.append(' ! 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))
|
|
descrip.append(' ! 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
|
|
rprec, rlevel = Productions[st_actionp[a].number].prec
|
|
sprec, slevel = Precedence.get(a, ('right', 0))
|
|
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:
|
|
descrip.append(' ! 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:
|
|
descrip.append(' ! 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]:
|
|
descrip.append(' %-15s %s' % (a, m))
|
|
_actprint[(a, m)] = 1
|
|
descrip.append('')
|
|
|
|
# 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
|
|
descrip.append(' %-30s shift and go to state %d' % (n, j))
|
|
|
|
action[st] = st_action
|
|
actionp[st] = st_actionp
|
|
goto[st] = st_goto
|
|
self.state_descriptions[st] = '\n'.join(descrip)
|
|
|
|
# ----------------------------------------------------------------------
|
|
# Debugging output. Printing the LRTable object will produce a listing
|
|
# of all of the states, conflicts, and other details.
|
|
# ----------------------------------------------------------------------
|
|
def __str__(self):
|
|
out = []
|
|
for descrip in self.state_descriptions.values():
|
|
out.append(descrip)
|
|
|
|
if self.sr_conflicts or self.rr_conflicts:
|
|
out.append('\nConflicts:\n')
|
|
|
|
for state, tok, resolution in self.sr_conflicts:
|
|
out.append('shift/reduce conflict for %s in state %d resolved as %s' % (tok, state, resolution))
|
|
|
|
already_reported = set()
|
|
for state, rule, rejected in self.rr_conflicts:
|
|
if (state, id(rule), id(rejected)) in already_reported:
|
|
continue
|
|
out.append('reduce/reduce conflict in state %d resolved using rule (%s)' % (state, rule))
|
|
out.append('rejected rule (%s) in state %d' % (rejected, state))
|
|
already_reported.add((state, id(rule), id(rejected)))
|
|
|
|
warned_never = set()
|
|
for state, rule, rejected in self.rr_conflicts:
|
|
if not rejected.reduced and (rejected not in warned_never):
|
|
out.append('Rule (%s) is never reduced' % rejected)
|
|
warned_never.add(rejected)
|
|
|
|
return '\n'.join(out)
|
|
|
|
# Collect grammar rules from a function
|
|
def _collect_grammar_rules(func):
|
|
grammar = []
|
|
while func:
|
|
prodname = func.__name__
|
|
unwrapped = inspect.unwrap(func)
|
|
filename = unwrapped.__code__.co_filename
|
|
lineno = unwrapped.__code__.co_firstlineno
|
|
for rule, lineno in zip(func.rules, range(lineno+len(func.rules)-1, 0, -1)):
|
|
syms = rule.split()
|
|
if syms[1:2] == [':'] or syms[1:2] == ['::=']:
|
|
grammar.append((func, filename, lineno, syms[0], syms[2:]))
|
|
else:
|
|
grammar.append((func, filename, lineno, prodname, syms))
|
|
func = getattr(func, 'next_func', None)
|
|
|
|
return grammar
|
|
|
|
class ParserMetaDict(OrderedDict):
|
|
'''
|
|
Dictionary that allows decorated grammar rule functions to be overloaded
|
|
'''
|
|
def __setitem__(self, key, value):
|
|
if key in self and callable(value) and hasattr(value, 'rules'):
|
|
value.next_func = self[key]
|
|
super().__setitem__(key, value)
|
|
|
|
class ParserMeta(type):
|
|
@classmethod
|
|
def __prepare__(meta, *args, **kwargs):
|
|
d = ParserMetaDict()
|
|
def _(rule, *extra):
|
|
rules = [rule, *extra]
|
|
def decorate(func):
|
|
func.rules = [ *getattr(func, 'rules', []), *rules[::-1] ]
|
|
return func
|
|
return decorate
|
|
d['_'] = _
|
|
return d
|
|
|
|
def __new__(meta, clsname, bases, attributes):
|
|
del attributes['_']
|
|
cls = super().__new__(meta, clsname, bases, attributes)
|
|
cls._build(list(attributes.items()))
|
|
return cls
|
|
|
|
class Parser(metaclass=ParserMeta):
|
|
# Logging object where debugging/diagnostic messages are sent
|
|
log = PlyLogger(sys.stderr)
|
|
|
|
# Debugging filename where parsetab.out data can be written
|
|
debugfile = None
|
|
|
|
@classmethod
|
|
def __validate_tokens(cls):
|
|
if not hasattr(cls, 'tokens'):
|
|
cls.log.error('No token list is defined')
|
|
return False
|
|
|
|
if not cls.tokens:
|
|
cls.log.error('tokens is empty')
|
|
return False
|
|
|
|
if 'error' in cls.tokens:
|
|
cls.log.error("Illegal token name 'error'. Is a reserved word")
|
|
return False
|
|
|
|
return True
|
|
|
|
@classmethod
|
|
def __validate_precedence(cls):
|
|
if not hasattr(cls, 'precedence'):
|
|
cls.__preclist = []
|
|
return True
|
|
|
|
preclist = []
|
|
if not isinstance(cls.precedence, (list, tuple)):
|
|
cls.log.error('precedence must be a list or tuple')
|
|
return False
|
|
|
|
for level, p in enumerate(cls.precedence, start=1):
|
|
if not isinstance(p, (list, tuple)):
|
|
cls.log.error('Bad precedence table entry %r. Must be a list or tuple', p)
|
|
return False
|
|
|
|
if len(p) < 2:
|
|
cls.log.error('Malformed precedence entry %s. Must be (assoc, term, ..., term)', p)
|
|
return False
|
|
|
|
if not all(isinstance(term, str) for term in p):
|
|
cls.log.error('precedence items must be strings')
|
|
return False
|
|
|
|
assoc = p[0]
|
|
preclist.extend((term, assoc, level) for term in p[1:])
|
|
|
|
cls.__preclist = preclist
|
|
return True
|
|
|
|
@classmethod
|
|
def __validate_specification(cls):
|
|
'''
|
|
Validate various parts of the grammar specification
|
|
'''
|
|
if not cls.__validate_tokens():
|
|
return False
|
|
if not cls.__validate_precedence():
|
|
return False
|
|
return True
|
|
|
|
@classmethod
|
|
def __build_grammar(cls, rules):
|
|
'''
|
|
Build the grammar from the grammar rules
|
|
'''
|
|
grammar_rules = []
|
|
fail = False
|
|
# Check for non-empty symbols
|
|
if not rules:
|
|
cls.log.error('no grammar rules are defined')
|
|
return False
|
|
|
|
grammar = Grammar(cls.tokens)
|
|
|
|
# Set the precedence level for terminals
|
|
for term, assoc, level in cls.__preclist:
|
|
try:
|
|
grammar.set_precedence(term, assoc, level)
|
|
except GrammarError as e:
|
|
cls.log.error(str(e))
|
|
fail = True
|
|
|
|
for name, func in rules:
|
|
try:
|
|
parsed_rule = _collect_grammar_rules(func)
|
|
for pfunc, rulefile, ruleline, prodname, syms in parsed_rule:
|
|
try:
|
|
grammar.add_production(prodname, syms, pfunc, rulefile, ruleline)
|
|
except GrammarError as e:
|
|
cls.log.error(str(e))
|
|
fail = True
|
|
except SyntaxError as e:
|
|
cls.log.error(str(e))
|
|
fail = True
|
|
try:
|
|
grammar.set_start(getattr(cls, 'start', None))
|
|
except GrammarError as e:
|
|
cls.log.error(str(e))
|
|
fail = True
|
|
|
|
undefined_symbols = grammar.undefined_symbols()
|
|
for sym, prod in undefined_symbols:
|
|
cls.log.error('%s:%d: Symbol %r used, but not defined as a token or a rule', prod.file, prod.line, sym)
|
|
fai = True
|
|
|
|
unused_terminals = grammar.unused_terminals()
|
|
for term in unused_terminals:
|
|
cls.log.warning('Token %r defined, but not used', term)
|
|
|
|
unused_rules = grammar.unused_rules()
|
|
for prod in unused_rules:
|
|
cls.log.warning('%s:%d: Rule %r defined, but not used', prod.file, prod.line, prod.name)
|
|
|
|
if len(unused_terminals) == 1:
|
|
cls.log.warning('There is 1 unused token')
|
|
if len(unused_terminals) > 1:
|
|
cls.log.warning('There are %d unused tokens', len(unused_terminals))
|
|
|
|
if len(unused_rules) == 1:
|
|
cls.log.warning('There is 1 unused rule')
|
|
if len(unused_rules) > 1:
|
|
cls.log.warning('There are %d unused rules', len(unused_rules))
|
|
|
|
unreachable = grammar.find_unreachable()
|
|
for u in unreachable:
|
|
cls.log.warning('Symbol %r is unreachable', u)
|
|
|
|
infinite = grammar.infinite_cycles()
|
|
for inf in infinite:
|
|
cls.log.error('Infinite recursion detected for symbol %r', inf)
|
|
fail = True
|
|
|
|
unused_prec = grammar.unused_precedence()
|
|
for term, assoc in unused_prec:
|
|
cls.log.error('Precedence rule %r defined for unknown symbol %r', assoc, term)
|
|
fail = True
|
|
|
|
cls._grammar = grammar
|
|
return not fail
|
|
|
|
@classmethod
|
|
def __build_lrtables(cls):
|
|
'''
|
|
Build the LR Parsing tables from the grammar
|
|
'''
|
|
lrtable = LRTable(cls._grammar)
|
|
num_sr = len(lrtable.sr_conflicts)
|
|
|
|
# Report shift/reduce and reduce/reduce conflicts
|
|
if num_sr != getattr(cls, 'expected_shift_reduce', None):
|
|
if num_sr == 1:
|
|
cls.log.warning('1 shift/reduce conflict')
|
|
elif num_sr > 1:
|
|
cls.log.warning('%d shift/reduce conflicts', num_sr)
|
|
|
|
num_rr = len(lrtable.rr_conflicts)
|
|
if num_rr != getattr(cls, 'expected_reduce_reduce', None):
|
|
if num_rr == 1:
|
|
cls.log.warning('1 reduce/reduce conflict')
|
|
elif num_rr > 1:
|
|
cls.log.warning('%d reduce/reduce conflicts', num_rr)
|
|
|
|
cls._lrtable = lrtable
|
|
return True
|
|
|
|
@classmethod
|
|
def __collect_rules(cls, definitions):
|
|
'''
|
|
Collect all of the tagged grammar rules
|
|
'''
|
|
rules = [ (name, value) for name, value in definitions
|
|
if callable(value) and hasattr(value, 'rules') ]
|
|
return rules
|
|
|
|
# ----------------------------------------------------------------------
|
|
# Build the LALR(1) tables. definitions is a list of (name, item) tuples
|
|
# of all definitions provided in the class, listed in the order in which
|
|
# they were defined. This method is triggered by a metaclass.
|
|
# ----------------------------------------------------------------------
|
|
@classmethod
|
|
def _build(cls, definitions):
|
|
if vars(cls).get('_build', False):
|
|
return
|
|
|
|
# Collect all of the grammar rules from the class definition
|
|
rules = cls.__collect_rules(definitions)
|
|
|
|
# Validate other parts of the grammar specification
|
|
if not cls.__validate_specification():
|
|
raise YaccError('Invalid parser specification')
|
|
|
|
# Build the underlying grammar object
|
|
if not cls.__build_grammar(rules):
|
|
raise YaccError('Invalid grammar')
|
|
|
|
# Build the LR tables
|
|
if not cls.__build_lrtables():
|
|
raise YaccError('Can\'t build parsing tables')
|
|
|
|
if cls.debugfile:
|
|
with open(cls.debugfile, 'w') as f:
|
|
f.write(str(cls._grammar))
|
|
f.write('\n')
|
|
f.write(str(cls._lrtable))
|
|
cls.log.info('Parser debugging for %s written to %s', cls.__qualname__, cls.debugfile)
|
|
|
|
# ----------------------------------------------------------------------
|
|
# Parsing Support. This is the parsing runtime that users use to
|
|
# ----------------------------------------------------------------------
|
|
def error(self, token):
|
|
'''
|
|
Default error handling function. This may be subclassed.
|
|
'''
|
|
if token:
|
|
lineno = getattr(token, 'lineno', 0)
|
|
if lineno:
|
|
sys.stderr.write('yacc: Syntax error at line %d, token=%s\n' % (lineno, token.type))
|
|
else:
|
|
sys.stderr.write('yacc: Syntax error, token=%s' % token.type)
|
|
else:
|
|
sys.stderr.write('yacc: Parse error in input. EOF\n')
|
|
|
|
def errok(self):
|
|
'''
|
|
Clear the error status
|
|
'''
|
|
self.errorok = True
|
|
|
|
def restart(self):
|
|
'''
|
|
Force the parser to restart from a fresh state. Clears the statestack
|
|
'''
|
|
del self.statestack[:]
|
|
del self.symstack[:]
|
|
sym = YaccSymbol()
|
|
sym.type = '$end'
|
|
self.symstack.append(sym)
|
|
self.statestack.append(0)
|
|
self.state = 0
|
|
|
|
def parse(self, tokens):
|
|
'''
|
|
Parse the given input tokens.
|
|
'''
|
|
lookahead = None # Current lookahead symbol
|
|
lookaheadstack = [] # Stack of lookahead symbols
|
|
actions = self._lrtable.lr_action # Local reference to action table (to avoid lookup on self.)
|
|
goto = self._lrtable.lr_goto # Local reference to goto table (to avoid lookup on self.)
|
|
prod = self._grammar.Productions # Local reference to production list (to avoid lookup on self.)
|
|
defaulted_states = self._lrtable.defaulted_states # Local reference to defaulted states
|
|
pslice = YaccProduction(None) # Production object passed to grammar rules
|
|
errorcount = 0 # Used during error recovery
|
|
|
|
# Set up the state and symbol stacks
|
|
self.tokens = tokens
|
|
self.statestack = statestack = [] # Stack of parsing states
|
|
self.symstack = symstack = [] # Stack of grammar symbols
|
|
pslice._stack = symstack # Associate the stack with the production
|
|
self.restart()
|
|
|
|
errtoken = None # Err token
|
|
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 self.state not in defaulted_states:
|
|
if not lookahead:
|
|
if not lookaheadstack:
|
|
lookahead = next(tokens, None) # Get the next token
|
|
else:
|
|
lookahead = lookaheadstack.pop()
|
|
if not lookahead:
|
|
lookahead = YaccSymbol()
|
|
lookahead.type = '$end'
|
|
|
|
# Check the action table
|
|
ltype = lookahead.type
|
|
t = actions[self.state].get(ltype)
|
|
else:
|
|
t = defaulted_states[self.state]
|
|
|
|
if t is not None:
|
|
if t > 0:
|
|
# shift a symbol on the stack
|
|
statestack.append(t)
|
|
self.state = t
|
|
|
|
symstack.append(lookahead)
|
|
lookahead = None
|
|
|
|
# Decrease error count on successful shift
|
|
if errorcount:
|
|
errorcount -= 1
|
|
continue
|
|
|
|
if t < 0:
|
|
# reduce a symbol on the stack, emit a production
|
|
self.production = p = prod[-t]
|
|
pname = p.name
|
|
plen = p.len
|
|
pslice._namemap = p.namemap
|
|
|
|
# Call the production function
|
|
pslice._slice = symstack[-plen:] if plen else []
|
|
|
|
sym = YaccSymbol()
|
|
sym.type = pname
|
|
sym.value = p.func(self, pslice)
|
|
if plen:
|
|
del symstack[-plen:]
|
|
del statestack[-plen:]
|
|
|
|
symstack.append(sym)
|
|
self.state = goto[statestack[-1]][pname]
|
|
statestack.append(self.state)
|
|
continue
|
|
|
|
if t == 0:
|
|
n = symstack[-1]
|
|
result = getattr(n, 'value', None)
|
|
return result
|
|
|
|
if t is None:
|
|
# We have some kind of parsing error here. To handle
|
|
# this, we are going to push the current token onto
|
|
# the tokenstack and replace it with an 'error' token.
|
|
# If there are any synchronization rules, they may
|
|
# catch it.
|
|
#
|
|
# In addition to pushing the error token, we call call
|
|
# the user defined error() function if this is the
|
|
# first syntax error. This function is only called if
|
|
# errorcount == 0.
|
|
if errorcount == 0 or self.errorok:
|
|
errorcount = ERROR_COUNT
|
|
self.errorok = False
|
|
if lookahead.type == '$end':
|
|
errtoken = None # End of file!
|
|
else:
|
|
errtoken = lookahead
|
|
|
|
tok = self.error(errtoken)
|
|
if tok:
|
|
# User must have done some kind of panic
|
|
# mode recovery on their own. The
|
|
# returned token is the next lookahead
|
|
lookahead = tok
|
|
self.errorok = True
|
|
continue
|
|
else:
|
|
# If at EOF. We just return. Basically dead.
|
|
if not errtoken:
|
|
return
|
|
else:
|
|
# Reset the error count. Unsuccessful token shifted
|
|
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 != '$end':
|
|
lookahead = None
|
|
self.state = 0
|
|
# Nuke the lookahead stack
|
|
del lookaheadstack[:]
|
|
continue
|
|
|
|
# case 2: the statestack has a couple of entries on it, but we're
|
|
# at the end of the file. nuke the top entry and generate an error token
|
|
|
|
# Start nuking entries on the stack
|
|
if lookahead.type == '$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
|
|
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 = lookahead.lineno
|
|
if hasattr(lookahead, 'index'):
|
|
t.index = lookahead.index
|
|
t.value = lookahead
|
|
lookaheadstack.append(lookahead)
|
|
lookahead = t
|
|
else:
|
|
sym = symstack.pop()
|
|
statestack.pop()
|
|
self.state = statestack[-1]
|
|
continue
|
|
|
|
# Call an error function here
|
|
raise RuntimeError('yacc: internal parser error!!!\n')
|