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Diffstat (limited to 'src/ply/yacc.py')
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diff --git a/src/ply/yacc.py b/src/ply/yacc.py new file mode 100644 index 0000000..6528796 --- /dev/null +++ b/src/ply/yacc.py @@ -0,0 +1,2482 @@ +# ----------------------------------------------------------------------------- +# 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 |