Merge ast-branch to head

This change implements a new bytecode compiler, based on a
transformation of the parse tree to an abstract syntax defined in
Parser/Python.asdl.

The compiler implementation is not complete, but it is in stable
enough shape to run the entire test suite excepting two disabled
tests.

1 files changed, 840 insertions, 0 deletions

diff --git a/Parser/spark.py b/Parser/spark.py
new file mode 100644
index 0000000..00d9733
--- /dev/null
+++ b/Parser/spark.py
@@ -0,0 +1,840 @@
+#  Copyright (c) 1998-2002 John Aycock
+#  
+#  Permission is hereby granted, free of charge, to any person obtaining
+#  a copy of this software and associated documentation files (the
+#  "Software"), to deal in the Software without restriction, including
+#  without limitation the rights to use, copy, modify, merge, publish,
+#  distribute, sublicense, and/or sell copies of the Software, and to
+#  permit persons to whom the Software is furnished to do so, subject to
+#  the following conditions:
+#  
+#  The above copyright notice and this permission notice shall be
+#  included in all copies or substantial portions of the Software.
+#  
+#  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+#  EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+#  MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
+#  IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
+#  CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
+#  TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
+#  SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+
+__version__ = 'SPARK-0.7 (pre-alpha-5)'
+
+import re
+import sys
+import string
+
+def _namelist(instance):
+	namelist, namedict, classlist = [], {}, [instance.__class__]
+	for c in classlist:
+		for b in c.__bases__:
+			classlist.append(b)
+		for name in c.__dict__.keys():
+			if not namedict.has_key(name):
+				namelist.append(name)
+				namedict[name] = 1
+	return namelist
+
+class GenericScanner:
+	def __init__(self, flags=0):
+		pattern = self.reflect()
+		self.re = re.compile(pattern, re.VERBOSE|flags)
+
+		self.index2func = {}
+		for name, number in self.re.groupindex.items():
+			self.index2func[number-1] = getattr(self, 't_' + name)
+
+	def makeRE(self, name):
+		doc = getattr(self, name).__doc__
+		rv = '(?P<%s>%s)' % (name[2:], doc)
+		return rv
+
+	def reflect(self):
+		rv = []
+		for name in _namelist(self):
+			if name[:2] == 't_' and name != 't_default':
+				rv.append(self.makeRE(name))
+
+		rv.append(self.makeRE('t_default'))
+		return string.join(rv, '|')
+
+	def error(self, s, pos):
+		print "Lexical error at position %s" % pos
+		raise SystemExit
+
+	def tokenize(self, s):
+		pos = 0
+		n = len(s)
+		while pos < n:
+			m = self.re.match(s, pos)
+			if m is None:
+				self.error(s, pos)
+
+			groups = m.groups()
+			for i in range(len(groups)):
+				if groups[i] and self.index2func.has_key(i):
+					self.index2func[i](groups[i])
+			pos = m.end()
+
+	def t_default(self, s):
+		r'( . | \n )+'
+		print "Specification error: unmatched input"
+		raise SystemExit
+
+#
+#  Extracted from GenericParser and made global so that [un]picking works.
+#
+class _State:
+	def __init__(self, stateno, items):
+		self.T, self.complete, self.items = [], [], items
+		self.stateno = stateno
+
+class GenericParser:
+	#
+	#  An Earley parser, as per J. Earley, "An Efficient Context-Free
+	#  Parsing Algorithm", CACM 13(2), pp. 94-102.  Also J. C. Earley,
+	#  "An Efficient Context-Free Parsing Algorithm", Ph.D. thesis,
+	#  Carnegie-Mellon University, August 1968.  New formulation of
+	#  the parser according to J. Aycock, "Practical Earley Parsing
+	#  and the SPARK Toolkit", Ph.D. thesis, University of Victoria,
+	#  2001, and J. Aycock and R. N. Horspool, "Practical Earley
+	#  Parsing", unpublished paper, 2001.
+	#
+
+	def __init__(self, start):
+		self.rules = {}
+		self.rule2func = {}
+		self.rule2name = {}
+		self.collectRules()
+		self.augment(start)
+		self.ruleschanged = 1
+
+	_NULLABLE = '\e_'
+	_START = 'START'
+	_BOF = '|-'
+
+	#
+	#  When pickling, take the time to generate the full state machine;
+	#  some information is then extraneous, too.  Unfortunately we
+	#  can't save the rule2func map.
+	#
+	def __getstate__(self):
+		if self.ruleschanged:
+			#
+			#  XXX - duplicated from parse()
+			#
+			self.computeNull()
+			self.newrules = {}
+			self.new2old = {}
+			self.makeNewRules()
+			self.ruleschanged = 0
+			self.edges, self.cores = {}, {}
+			self.states = { 0: self.makeState0() }
+			self.makeState(0, self._BOF)
+		#
+		#  XXX - should find a better way to do this..
+		#
+		changes = 1
+		while changes:
+			changes = 0
+			for k, v in self.edges.items():
+				if v is None:
+					state, sym = k
+					if self.states.has_key(state):
+						self.goto(state, sym)
+						changes = 1
+		rv = self.__dict__.copy()
+		for s in self.states.values():
+			del s.items
+		del rv['rule2func']
+		del rv['nullable']
+		del rv['cores']
+		return rv
+
+	def __setstate__(self, D):
+		self.rules = {}
+		self.rule2func = {}
+		self.rule2name = {}
+		self.collectRules()
+		start = D['rules'][self._START][0][1][1]	# Blech.
+		self.augment(start)
+		D['rule2func'] = self.rule2func
+		D['makeSet'] = self.makeSet_fast
+		self.__dict__ = D
+
+	#
+	#  A hook for GenericASTBuilder and GenericASTMatcher.  Mess
+	#  thee not with this; nor shall thee toucheth the _preprocess
+	#  argument to addRule.
+	#
+	def preprocess(self, rule, func):	return rule, func
+
+	def addRule(self, doc, func, _preprocess=1):
+		fn = func
+		rules = string.split(doc)
+
+		index = []
+		for i in range(len(rules)):
+			if rules[i] == '::=':
+				index.append(i-1)
+		index.append(len(rules))
+
+		for i in range(len(index)-1):
+			lhs = rules[index[i]]
+			rhs = rules[index[i]+2:index[i+1]]
+			rule = (lhs, tuple(rhs))
+
+			if _preprocess:
+				rule, fn = self.preprocess(rule, func)
+
+			if self.rules.has_key(lhs):
+				self.rules[lhs].append(rule)
+			else:
+				self.rules[lhs] = [ rule ]
+			self.rule2func[rule] = fn
+			self.rule2name[rule] = func.__name__[2:]
+		self.ruleschanged = 1
+
+	def collectRules(self):
+		for name in _namelist(self):
+			if name[:2] == 'p_':
+				func = getattr(self, name)
+				doc = func.__doc__
+				self.addRule(doc, func)
+
+	def augment(self, start):
+		rule = '%s ::= %s %s' % (self._START, self._BOF, start)
+		self.addRule(rule, lambda args: args[1], 0)
+
+	def computeNull(self):
+		self.nullable = {}
+		tbd = []
+
+		for rulelist in self.rules.values():
+			lhs = rulelist[0][0]
+			self.nullable[lhs] = 0
+			for rule in rulelist:
+				rhs = rule[1]
+				if len(rhs) == 0:
+					self.nullable[lhs] = 1
+					continue
+				#
+				#  We only need to consider rules which
+				#  consist entirely of nonterminal symbols.
+				#  This should be a savings on typical
+				#  grammars.
+				#
+				for sym in rhs:
+					if not self.rules.has_key(sym):
+						break
+				else:
+					tbd.append(rule)
+		changes = 1
+		while changes:
+			changes = 0
+			for lhs, rhs in tbd:
+				if self.nullable[lhs]:
+					continue
+				for sym in rhs:
+					if not self.nullable[sym]:
+						break
+				else:
+					self.nullable[lhs] = 1
+					changes = 1
+
+	def makeState0(self):
+		s0 = _State(0, [])
+		for rule in self.newrules[self._START]:
+			s0.items.append((rule, 0))
+		return s0
+
+	def finalState(self, tokens):
+		#
+		#  Yuck.
+		#
+		if len(self.newrules[self._START]) == 2 and len(tokens) == 0:
+			return 1
+		start = self.rules[self._START][0][1][1]
+		return self.goto(1, start)
+
+	def makeNewRules(self):
+		worklist = []
+		for rulelist in self.rules.values():
+			for rule in rulelist:
+				worklist.append((rule, 0, 1, rule))
+
+		for rule, i, candidate, oldrule in worklist:
+			lhs, rhs = rule
+			n = len(rhs)
+			while i < n:
+				sym = rhs[i]
+				if not self.rules.has_key(sym) or \
+				   not self.nullable[sym]:
+					candidate = 0
+					i = i + 1
+					continue
+
+				newrhs = list(rhs)
+				newrhs[i] = self._NULLABLE+sym
+				newrule = (lhs, tuple(newrhs))
+				worklist.append((newrule, i+1,
+						 candidate, oldrule))
+				candidate = 0
+				i = i + 1
+			else:
+				if candidate:
+					lhs = self._NULLABLE+lhs
+					rule = (lhs, rhs)
+				if self.newrules.has_key(lhs):
+					self.newrules[lhs].append(rule)
+				else:
+					self.newrules[lhs] = [ rule ]
+				self.new2old[rule] = oldrule
+	
+	def typestring(self, token):
+		return None
+
+	def error(self, token):
+		print "Syntax error at or near `%s' token" % token
+		raise SystemExit
+
+	def parse(self, tokens):
+		sets = [ [(1,0), (2,0)] ]
+		self.links = {}
+		
+		if self.ruleschanged:
+			self.computeNull()
+			self.newrules = {}
+			self.new2old = {}
+			self.makeNewRules()
+			self.ruleschanged = 0
+			self.edges, self.cores = {}, {}
+			self.states = { 0: self.makeState0() }
+			self.makeState(0, self._BOF)
+
+		for i in xrange(len(tokens)):
+			sets.append([])
+
+			if sets[i] == []:
+				break				
+			self.makeSet(tokens[i], sets, i)
+		else:
+			sets.append([])
+			self.makeSet(None, sets, len(tokens))
+
+		#_dump(tokens, sets, self.states)
+
+		finalitem = (self.finalState(tokens), 0)
+		if finalitem not in sets[-2]:
+			if len(tokens) > 0:
+				self.error(tokens[i-1])
+			else:
+				self.error(None)
+
+		return self.buildTree(self._START, finalitem,
+				      tokens, len(sets)-2)
+
+	def isnullable(self, sym):
+		#
+		#  For symbols in G_e only.  If we weren't supporting 1.5,
+		#  could just use sym.startswith().
+		#
+		return self._NULLABLE == sym[0:len(self._NULLABLE)]
+
+	def skip(self, (lhs, rhs), pos=0):
+		n = len(rhs)
+		while pos < n:
+			if not self.isnullable(rhs[pos]):
+				break
+			pos = pos + 1
+		return pos
+
+	def makeState(self, state, sym):
+		assert sym is not None
+		#
+		#  Compute \epsilon-kernel state's core and see if
+		#  it exists already.
+		#
+		kitems = []
+		for rule, pos in self.states[state].items:
+			lhs, rhs = rule
+			if rhs[pos:pos+1] == (sym,):
+				kitems.append((rule, self.skip(rule, pos+1)))
+		core = kitems
+
+		core.sort()
+		tcore = tuple(core)
+		if self.cores.has_key(tcore):
+			return self.cores[tcore]
+		#
+		#  Nope, doesn't exist.  Compute it and the associated
+		#  \epsilon-nonkernel state together; we'll need it right away.
+		#
+		k = self.cores[tcore] = len(self.states)
+		K, NK = _State(k, kitems), _State(k+1, [])
+		self.states[k] = K
+		predicted = {}
+
+		edges = self.edges
+		rules = self.newrules
+		for X in K, NK:
+			worklist = X.items
+			for item in worklist:
+				rule, pos = item
+				lhs, rhs = rule
+				if pos == len(rhs):
+					X.complete.append(rule)
+					continue
+
+				nextSym = rhs[pos]
+				key = (X.stateno, nextSym)
+				if not rules.has_key(nextSym):
+					if not edges.has_key(key):
+						edges[key] = None
+						X.T.append(nextSym)
+				else:
+					edges[key] = None
+					if not predicted.has_key(nextSym):
+						predicted[nextSym] = 1
+						for prule in rules[nextSym]:
+							ppos = self.skip(prule)
+							new = (prule, ppos)
+							NK.items.append(new)
+			#
+			#  Problem: we know K needs generating, but we
+			#  don't yet know about NK.  Can't commit anything
+			#  regarding NK to self.edges until we're sure.  Should
+			#  we delay committing on both K and NK to avoid this
+			#  hacky code?  This creates other problems..
+			#
+			if X is K:
+				edges = {}
+
+		if NK.items == []:
+			return k
+
+		#
+		#  Check for \epsilon-nonkernel's core.  Unfortunately we
+		#  need to know the entire set of predicted nonterminals
+		#  to do this without accidentally duplicating states.
+		#
+		core = predicted.keys()
+		core.sort()
+		tcore = tuple(core)
+		if self.cores.has_key(tcore):
+			self.edges[(k, None)] = self.cores[tcore]
+			return k
+
+		nk = self.cores[tcore] = self.edges[(k, None)] = NK.stateno
+		self.edges.update(edges)
+		self.states[nk] = NK
+		return k
+
+	def goto(self, state, sym):
+		key = (state, sym)
+		if not self.edges.has_key(key):
+			#
+			#  No transitions from state on sym.
+			#
+			return None
+
+		rv = self.edges[key]
+		if rv is None:
+			#
+			#  Target state isn't generated yet.  Remedy this.
+			#
+			rv = self.makeState(state, sym)
+			self.edges[key] = rv
+		return rv
+
+	def gotoT(self, state, t):
+		return [self.goto(state, t)]
+
+	def gotoST(self, state, st):
+		rv = []
+		for t in self.states[state].T:
+			if st == t:
+				rv.append(self.goto(state, t))
+		return rv
+
+	def add(self, set, item, i=None, predecessor=None, causal=None):
+		if predecessor is None:
+			if item not in set:
+				set.append(item)
+		else:
+			key = (item, i)
+			if item not in set:
+				self.links[key] = []
+				set.append(item)
+			self.links[key].append((predecessor, causal))
+
+	def makeSet(self, token, sets, i):
+		cur, next = sets[i], sets[i+1]
+
+		ttype = token is not None and self.typestring(token) or None
+		if ttype is not None:
+			fn, arg = self.gotoT, ttype
+		else:
+			fn, arg = self.gotoST, token
+
+		for item in cur:
+			ptr = (item, i)
+			state, parent = item
+			add = fn(state, arg)
+			for k in add:
+				if k is not None:
+					self.add(next, (k, parent), i+1, ptr)
+					nk = self.goto(k, None)
+					if nk is not None:
+						self.add(next, (nk, i+1))
+
+			if parent == i:
+				continue
+
+			for rule in self.states[state].complete:
+				lhs, rhs = rule
+				for pitem in sets[parent]:
+					pstate, pparent = pitem
+					k = self.goto(pstate, lhs)
+					if k is not None:
+						why = (item, i, rule)
+						pptr = (pitem, parent)
+						self.add(cur, (k, pparent),
+							 i, pptr, why)
+						nk = self.goto(k, None)
+						if nk is not None:
+							self.add(cur, (nk, i))
+
+	def makeSet_fast(self, token, sets, i):
+		#
+		#  Call *only* when the entire state machine has been built!
+		#  It relies on self.edges being filled in completely, and
+		#  then duplicates and inlines code to boost speed at the
+		#  cost of extreme ugliness.
+		#
+		cur, next = sets[i], sets[i+1]
+		ttype = token is not None and self.typestring(token) or None
+
+		for item in cur:
+			ptr = (item, i)
+			state, parent = item
+			if ttype is not None:
+				k = self.edges.get((state, ttype), None)
+				if k is not None:
+					#self.add(next, (k, parent), i+1, ptr)
+					#INLINED --v
+					new = (k, parent)
+					key = (new, i+1)
+					if new not in next:
+						self.links[key] = []
+						next.append(new)
+					self.links[key].append((ptr, None))
+					#INLINED --^
+					#nk = self.goto(k, None)
+					nk = self.edges.get((k, None), None)
+					if nk is not None:
+						#self.add(next, (nk, i+1))
+						#INLINED --v
+						new = (nk, i+1)
+						if new not in next:
+							next.append(new)
+						#INLINED --^
+			else:
+				add = self.gotoST(state, token)
+				for k in add:
+					if k is not None:
+						self.add(next, (k, parent), i+1, ptr)
+						#nk = self.goto(k, None)
+						nk = self.edges.get((k, None), None)
+						if nk is not None:
+							self.add(next, (nk, i+1))
+
+			if parent == i:
+				continue
+
+			for rule in self.states[state].complete:
+				lhs, rhs = rule
+				for pitem in sets[parent]:
+					pstate, pparent = pitem
+					#k = self.goto(pstate, lhs)
+					k = self.edges.get((pstate, lhs), None)
+					if k is not None:
+						why = (item, i, rule)
+						pptr = (pitem, parent)
+						#self.add(cur, (k, pparent),
+						#	 i, pptr, why)
+						#INLINED --v
+						new = (k, pparent)
+						key = (new, i)
+						if new not in cur:
+							self.links[key] = []
+							cur.append(new)
+						self.links[key].append((pptr, why))
+						#INLINED --^
+						#nk = self.goto(k, None)
+						nk = self.edges.get((k, None), None)
+						if nk is not None:
+							#self.add(cur, (nk, i))
+							#INLINED --v
+							new = (nk, i)
+							if new not in cur:
+								cur.append(new)
+							#INLINED --^
+
+	def predecessor(self, key, causal):
+		for p, c in self.links[key]:
+			if c == causal:
+				return p
+		assert 0
+
+	def causal(self, key):
+		links = self.links[key]
+		if len(links) == 1:
+			return links[0][1]
+		choices = []
+		rule2cause = {}
+		for p, c in links:
+			rule = c[2]
+			choices.append(rule)
+			rule2cause[rule] = c
+		return rule2cause[self.ambiguity(choices)]
+
+	def deriveEpsilon(self, nt):
+		if len(self.newrules[nt]) > 1:
+			rule = self.ambiguity(self.newrules[nt])
+		else:
+			rule = self.newrules[nt][0]
+		#print rule
+
+		rhs = rule[1]
+		attr = [None] * len(rhs)
+
+		for i in range(len(rhs)-1, -1, -1):
+			attr[i] = self.deriveEpsilon(rhs[i])
+		return self.rule2func[self.new2old[rule]](attr)
+
+	def buildTree(self, nt, item, tokens, k):
+		state, parent = item
+
+		choices = []
+		for rule in self.states[state].complete:
+			if rule[0] == nt:
+				choices.append(rule)
+		rule = choices[0]
+		if len(choices) > 1:
+			rule = self.ambiguity(choices)
+		#print rule
+
+		rhs = rule[1]
+		attr = [None] * len(rhs)
+
+		for i in range(len(rhs)-1, -1, -1):
+			sym = rhs[i]
+			if not self.newrules.has_key(sym):
+				if sym != self._BOF:
+					attr[i] = tokens[k-1]
+					key = (item, k)
+					item, k = self.predecessor(key, None)
+			#elif self.isnullable(sym):
+			elif self._NULLABLE == sym[0:len(self._NULLABLE)]:
+				attr[i] = self.deriveEpsilon(sym)
+			else:
+				key = (item, k)
+				why = self.causal(key)
+				attr[i] = self.buildTree(sym, why[0],
+							 tokens, why[1])
+				item, k = self.predecessor(key, why)
+		return self.rule2func[self.new2old[rule]](attr)
+
+	def ambiguity(self, rules):
+		#
+		#  XXX - problem here and in collectRules() if the same rule
+		#	 appears in >1 method.  Also undefined results if rules
+		#	 causing the ambiguity appear in the same method.
+		#
+		sortlist = []
+		name2index = {}
+		for i in range(len(rules)):
+			lhs, rhs = rule = rules[i]
+			name = self.rule2name[self.new2old[rule]]
+			sortlist.append((len(rhs), name))
+			name2index[name] = i
+		sortlist.sort()
+		list = map(lambda (a,b): b, sortlist)
+		return rules[name2index[self.resolve(list)]]
+
+	def resolve(self, list):
+		#
+		#  Resolve ambiguity in favor of the shortest RHS.
+		#  Since we walk the tree from the top down, this
+		#  should effectively resolve in favor of a "shift".
+		#
+		return list[0]
+
+#
+#  GenericASTBuilder automagically constructs a concrete/abstract syntax tree
+#  for a given input.  The extra argument is a class (not an instance!)
+#  which supports the "__setslice__" and "__len__" methods.
+#
+#  XXX - silently overrides any user code in methods.
+#
+
+class GenericASTBuilder(GenericParser):
+	def __init__(self, AST, start):
+		GenericParser.__init__(self, start)
+		self.AST = AST
+
+	def preprocess(self, rule, func):
+		rebind = lambda lhs, self=self: \
+				lambda args, lhs=lhs, self=self: \
+					self.buildASTNode(args, lhs)
+		lhs, rhs = rule
+		return rule, rebind(lhs)
+
+	def buildASTNode(self, args, lhs):
+		children = []
+		for arg in args:
+			if isinstance(arg, self.AST):
+				children.append(arg)
+			else:
+				children.append(self.terminal(arg))
+		return self.nonterminal(lhs, children)
+
+	def terminal(self, token):	return token
+
+	def nonterminal(self, type, args):
+		rv = self.AST(type)
+		rv[:len(args)] = args
+		return rv
+
+#
+#  GenericASTTraversal is a Visitor pattern according to Design Patterns.  For
+#  each node it attempts to invoke the method n_<node type>, falling
+#  back onto the default() method if the n_* can't be found.  The preorder
+#  traversal also looks for an exit hook named n_<node type>_exit (no default
+#  routine is called if it's not found).  To prematurely halt traversal
+#  of a subtree, call the prune() method -- this only makes sense for a
+#  preorder traversal.  Node type is determined via the typestring() method.
+#
+
+class GenericASTTraversalPruningException:
+	pass
+
+class GenericASTTraversal:
+	def __init__(self, ast):
+		self.ast = ast
+
+	def typestring(self, node):
+		return node.type
+
+	def prune(self):
+		raise GenericASTTraversalPruningException
+
+	def preorder(self, node=None):
+		if node is None:
+			node = self.ast
+
+		try:
+			name = 'n_' + self.typestring(node)
+			if hasattr(self, name):
+				func = getattr(self, name)
+				func(node)
+			else:
+				self.default(node)
+		except GenericASTTraversalPruningException:
+			return
+
+		for kid in node:
+			self.preorder(kid)
+
+		name = name + '_exit'
+		if hasattr(self, name):
+			func = getattr(self, name)
+			func(node)
+
+	def postorder(self, node=None):
+		if node is None:
+			node = self.ast
+
+		for kid in node:
+			self.postorder(kid)
+
+		name = 'n_' + self.typestring(node)
+		if hasattr(self, name):
+			func = getattr(self, name)
+			func(node)
+		else:
+			self.default(node)
+
+
+	def default(self, node):
+		pass
+
+#
+#  GenericASTMatcher.  AST nodes must have "__getitem__" and "__cmp__"
+#  implemented.
+#
+#  XXX - makes assumptions about how GenericParser walks the parse tree.
+#
+
+class GenericASTMatcher(GenericParser):
+	def __init__(self, start, ast):
+		GenericParser.__init__(self, start)
+		self.ast = ast
+
+	def preprocess(self, rule, func):
+		rebind = lambda func, self=self: \
+				lambda args, func=func, self=self: \
+					self.foundMatch(args, func)
+		lhs, rhs = rule
+		rhslist = list(rhs)
+		rhslist.reverse()
+
+		return (lhs, tuple(rhslist)), rebind(func)
+
+	def foundMatch(self, args, func):
+		func(args[-1])
+		return args[-1]
+
+	def match_r(self, node):
+		self.input.insert(0, node)
+		children = 0
+
+		for child in node:
+			if children == 0:
+				self.input.insert(0, '(')
+			children = children + 1
+			self.match_r(child)
+
+		if children > 0:
+			self.input.insert(0, ')')
+
+	def match(self, ast=None):
+		if ast is None:
+			ast = self.ast
+		self.input = []
+
+		self.match_r(ast)
+		self.parse(self.input)
+
+	def resolve(self, list):
+		#
+		#  Resolve ambiguity in favor of the longest RHS.
+		#
+		return list[-1]
+
+def _dump(tokens, sets, states):
+	for i in range(len(sets)):
+		print 'set', i
+		for item in sets[i]:
+			print '\t', item
+			for (lhs, rhs), pos in states[item[0]].items:
+				print '\t\t', lhs, '::=',
+				print string.join(rhs[:pos]),
+				print '.',
+				print string.join(rhs[pos:])
+		if i < len(tokens):
+			print
+			print 'token', str(tokens[i])
+			print