All relevant tests passing. Also indentation and other refactoring.

lark/parser_frontends.py

@@ -1,10 +1,11 @@
 import re
 from .utils import get_regexp_width
 
-from parsers.grammar_analysis import GrammarAnalyzer
+from .parsers.grammar_analysis import GrammarAnalyzer
 from .lexer import Lexer, ContextualLexer, Token
 
-from .common import is_terminal, GrammarError, Terminal_Regexp, Terminal_Token
+from .common import GrammarError
+from .common import is_terminal, GrammarError
 from .parsers import lalr_parser, earley, xearley, resolve_ambig, cyk
 from .tree import Tree
 
@@ -137,31 +138,36 @@ class XEarley:
         return self.parser.parse(text)
 
 
+class Earley(WithLexer):
+    def __init__(self, lexer_conf, parser_conf, options=None):
+        self.init_traditional_lexer(lexer_conf)
+
+        self.parser = earley.Parser(parser_conf, self.match,
+                                    resolve_ambiguity=get_ambiguity_resolver(options))
+
+    def match(self, term, token):
+        return term == token.type
+
+    def parse(self, text):
+        tokens = self.lex(text)
+        return self.parser.parse(tokens)
+
 class CYK(WithLexer):
 
   def __init__(self, lexer_conf, parser_conf, options=None):
-    WithLexer.__init__(self, lexer_conf)
-    # TokenDef from synthetic rule to terminal value
-    self._token_by_name = {t.name: t for t in lexer_conf.tokens}
-    rules = [(lhs, self._prepare_expansion(rhs), cb, opt) for lhs, rhs, cb, opt in parser_conf.rules]
-    self._analysis = GrammarAnalyzer(rules, parser_conf.start)
+    self.init_traditional_lexer(lexer_conf)
+
+    self._analysis = GrammarAnalyzer(parser_conf)
     self._parser = cyk.Parser(self._analysis.rules, parser_conf.start)
 
     self._postprocess = {}
     for rule in self._analysis.rules:
-        if rule.origin != '$root':  # XXX kinda ugly
-            a = rule.alias
-            self._postprocess[a] = a if callable(a) else (a and getattr(parser_conf.callback, a))
-
-  def _prepare_expansion(self, expansion):
-    return [
-        Terminal_Regexp(sym, self._token_by_name[sym].pattern.to_regexp())
-        if is_terminal(sym) else sym for sym in expansion
-    ]
+        a = rule.alias
+        self._postprocess[a] = a if callable(a) else (a and getattr(parser_conf.callback, a))
 
   def parse(self, text):
-    tokenized = [token.value for token in self.lex(text)]
-    parse = self._parser.parse(tokenized)
+    tokens = list(self.lex(text))
+    parse = self._parser.parse(tokens)
     parse = self._transform(parse)
     return parse
 

lark/parsers/cyk.py

@@ -1,225 +1,193 @@
 """This module implements a CYK parser."""
+
 from collections import defaultdict
 import itertools
-import re
 
-from ..common import ParseError, Terminal, Terminal_Regexp
+from ..common import ParseError, is_terminal
 from ..lexer import Token
 from ..tree import Tree
 
-
-def TypeName(x):
-  return type(x).__name__
-
+try:
+    xrange
+except NameError:
+    xrange = range
 
 class Symbol(object):
-  """Any grammar symbol."""
+    """Any grammar symbol."""
 
-  def __init__(self, s):
-    self.s = s
+    def __init__(self, s):
+        self.s = s
 
-  def __repr__(self):
-    return '%s(%s)' % (TypeName(self), str(self))
+    def __repr__(self):
+        return '%s(%s)' % (type(self).__name__, str(self))
 
-  def __str__(self):
-    return str(self.s)
+    def __str__(self):
+        return str(self.s)
 
-  def __eq__(self, other):
-    return str(self) == str(other)
+    def __eq__(self, other):
+        return self.s == str(other)
 
-  def __ne__(self, other):
-    return not self.__eq__(other)
+    def __ne__(self, other):
+        return not self.__eq__(other)
 
-  def __hash__(self):
-    return hash(TypeName(self) + '&' + self.__str__())
+    def __hash__(self):
+        return hash((type(self), str(self.s)))
 
 
 class T(Symbol):
-  """Terminal."""
-
-  def __init__(self, s):
-    super(T, self).__init__(s)
-    self.regexp = re.compile(s)
+    """Terminal."""
 
-  def match(self, s):
-    m = self.regexp.match(s)
-    return bool(m) and len(m.group(0)) == len(s)
-
-  def __eq__(self, other):
-    return super(T, self).__eq__(other) and isinstance(other, T)
+    def match(self, s):
+        return self.s == s.type
 
 
 class NT(Symbol):
-  """Non-terminal."""
-
-  def __eq__(self, other):
-    return super(NT, self).__eq__(other) and isinstance(other, NT)
+    """Non-terminal."""
+    pass
 
 
 class Rule(object):
-  """Context-free grammar rule."""
+    """Context-free grammar rule."""
 
-  def __init__(self, lhs, rhs, weight, alias):
-    super(Rule, self).__init__()
-    assert isinstance(lhs, NT), lhs
-    assert all(isinstance(x, NT) or isinstance(x, T) for x in rhs), rhs
-    self.lhs = lhs
-    self.rhs = rhs
-    self.weight = weight
-    self.alias = alias
+    def __init__(self, lhs, rhs, weight, alias):
+        super(Rule, self).__init__()
+        assert isinstance(lhs, NT), lhs
+        assert all(isinstance(x, NT) or isinstance(x, T) for x in rhs), rhs
+        self.lhs = lhs
+        self.rhs = rhs
+        self.weight = weight
+        self.alias = alias
 
-  def __str__(self):
-    return '%s -> %s' % (str(self.lhs), ' '.join(str(x) for x in self.rhs))
+    def __str__(self):
+        return '%s -> %s' % (str(self.lhs), ' '.join(str(x) for x in self.rhs))
 
-  def __repr__(self):
-    return str(self)
+    def __repr__(self):
+        return str(self)
 
-  def __hash__(self):
-    return hash(self.__repr__())
+    def __hash__(self):
+        return hash((self.lhs, tuple(self.rhs)))
 
-  def __eq__(self, other):
-    return self.lhs == other.lhs and self.rhs == other.rhs
+    def __eq__(self, other):
+        return self.lhs == other.lhs and self.rhs == other.rhs
 
-  def __ne__(self, other):
-    return not self.__eq__(other)
+    def __ne__(self, other):
+        return not (self == other)
 
 
 class Grammar(object):
-  """Context-free grammar."""
+    """Context-free grammar."""
 
-  def __init__(self, rules):
-    super(Grammar, self).__init__()
-    self.rules = sorted(rules, key=lambda x: str(x))
+    def __init__(self, rules):
+        super(Grammar, self).__init__()
+        self.rules = rules
 
-  def __eq__(self, other):
-    return set(self.rules) == set(other.rules)
+    def __eq__(self, other):
+        return set(self.rules) == set(other.rules)
 
-  def __str__(self):
-    return '\n' + '\n'.join(sorted(x.__repr__() for x in self.rules)) + '\n'
+    def __str__(self):
+        return '\n' + '\n'.join(sorted(repr(x) for x in self.rules)) + '\n'
 
-  def __repr__(self):
-    return str(self)
+    def __repr__(self):
+        return str(self)
 
 
 # Parse tree data structures
 class RuleNode(object):
-  """A node in the parse tree, which also contains the full rhs rule."""
-
-  def __init__(self, rule, children, weight=0):
-    super(RuleNode, self).__init__()
-    self.rule = rule
-    self.children = children
-    self.weight = weight
-
-  def __repr__(self):
-    return 'RuleNode(%s, [%s])' % (repr(self.rule.lhs), ', '.join(
-        str(x) for x in self.children))
+    """A node in the parse tree, which also contains the full rhs rule."""
 
-  def __hash__(self):
-    return hash(self.__repr__())
+    def __init__(self, rule, children, weight=0):
+        self.rule = rule
+        self.children = children
+        self.weight = weight
 
+    def __repr__(self):
+        return 'RuleNode(%s, [%s])' % (repr(self.rule.lhs), ', '.join(str(x) for x in self.children))
 
-class Node(object):
-  """A node in the parse tree."""
-
-  def __init__(self, lhs, children):
-    super(Node, self).__init__()
-    self.lhs = lhs
-    self.children = children
-
-  def __repr__(self):
-    return 'Node(%s, [%s])' % (repr(self.lhs), ', '.join(
-        str(x) for x in self.children))
-
-  def __hash__(self):
-    return hash(self.__repr__())
 
 
 class Parser(object):
-  """Parser wrapper."""
-
-  def __init__(self, rules, start):
-    super(Parser, self).__init__()
-    self.orig_rules = {rule.alias: rule for rule in rules}
-    rules = [self._ToRule(rule) for rule in rules]
-    self.grammar = ToCnf(Grammar(rules))
-    self.start = NT(start)
-
-  def _ToRule(self, lark_rule):
-    """Converts a lark rule, (lhs, rhs, callback, options), to a Rule."""
-    return Rule(
-        NT(lark_rule.origin), [
-            T(x.data) if (isinstance(x, Terminal_Regexp) or
-                          isinstance(x, Terminal)) else NT(x)
-            for x in lark_rule.expansion
-        ], weight=lark_rule.options.priority if lark_rule.options and lark_rule.options.priority else 0, alias=lark_rule.alias)
-
-  def parse(self, tokenized):  # pylint: disable=invalid-name
-    """Parses input, which is a list of tokens."""
-    table, trees = _Parse(tokenized, self.grammar)
-    # Check if the parse succeeded.
-    if all(r.lhs != self.start for r in table[(0, len(tokenized) - 1)]):
-      raise ParseError('Parsing failed.')
-    parse = trees[(0, len(tokenized) - 1)][NT(self.start)]
-    return self._ToTree(RevertCnf(parse))
-
-  def _ToTree(self, rule_node):
-    """Converts a RuleNode parse tree to a lark Tree."""
-    orig_rule = self.orig_rules[rule_node.rule.alias]
-    children = []
-    for i, child in enumerate(rule_node.children):
-      if isinstance(child, RuleNode):
-        children.append(self._ToTree(child))
-      elif isinstance(child, Terminal_Regexp):
-        children.append(Token(orig_rule.expansion[i].name, child.s))
-      else:
-        children.append(Token(orig_rule.expansion[i], child.s))
-    return Tree(orig_rule.origin, children, rule=orig_rule)
+    """Parser wrapper."""
+
+    def __init__(self, rules, start):
+        super(Parser, self).__init__()
+        self.orig_rules = {rule.alias: rule for rule in rules}
+        rules = [self._ToRule(rule) for rule in rules]
+        self.grammar = ToCnf(Grammar(rules))
+        self.start = NT(start)
+
+    def _ToRule(self, lark_rule):
+        """Converts a lark rule, (lhs, rhs, callback, options), to a Rule."""
+        return Rule(
+            NT(lark_rule.origin), [
+                T(x) if is_terminal(x) else NT(x) for x in lark_rule.expansion
+            ], weight=lark_rule.options.priority if lark_rule.options and lark_rule.options.priority else 0, alias=lark_rule.alias)
+
+    def parse(self, tokenized):  # pylint: disable=invalid-name
+        """Parses input, which is a list of tokens."""
+        table, trees = _parse(tokenized, self.grammar)
+        # Check if the parse succeeded.
+        if all(r.lhs != self.start for r in table[(0, len(tokenized) - 1)]):
+            raise ParseError('Parsing failed.')
+        parse = trees[(0, len(tokenized) - 1)][NT(self.start)]
+        return self._ToTree(RevertCnf(parse))
+
+    def _ToTree(self, rule_node):
+        """Converts a RuleNode parse tree to a lark Tree."""
+        orig_rule = self.orig_rules[rule_node.rule.alias]
+        children = []
+        for i, child in enumerate(rule_node.children):
+            if isinstance(child, RuleNode):
+                children.append(self._ToTree(child))
+            else:
+                assert isinstance(child.s, Token)
+                children.append(child.s)
+        return Tree(orig_rule.origin, children, rule=orig_rule)
 
 
 def PrintParse(node, indent=0):
-  if isinstance(node, RuleNode):
-    print(' ' * (indent * 2) + str(node.rule.lhs))
-    for child in node.children:
-      PrintParse(child, indent + 1)
-  else:
-    print(' ' * (indent * 2) + str(node.s))
-
-
-def _Parse(s, g):
-  """Parses sentence 's' using CNF grammar 'g'."""
-  # The CYK table. Indexed with a 2-tuple: (start pos, end pos)
-  table = defaultdict(set)
-  # Top-level structure is similar to the CYK table. Each cell is a dict from
-  # rule name to the best (lightest) tree for that rule.
-  trees = defaultdict(dict)
-  # Populate base case with existing terminal production rules
-  for i, w in enumerate(s):
-    for terminal, rules in g.terminal_rules.iteritems():
-      if terminal.match(w):
-        for rule in rules:
-          table[(i, i)].add(rule)
-          if (rule.lhs not in trees[(i, i)] or
-              rule.weight < trees[(i, i)][rule.lhs].weight):
-            trees[(i, i)][rule.lhs] = RuleNode(rule, [T(w)], weight=rule.weight)
-  # Iterate over lengths of sub-sentences
-  for l in xrange(2, len(s) + 1):
-    # Iterate over sub-sentences with the given length
-    for i in xrange(len(s) - l + 1):
-      # Choose partition of the sub-sentence in [1, l)
-      for p in xrange(i + 1, i + l):
-        span1 = (i, p - 1)
-        span2 = (p, i + l - 1)
-        for r1, r2 in itertools.product(table[span1], table[span2]):
-          for rule in g.nonterminal_rules.get((r1.lhs, r2.lhs), []):
-            table[(i, i + l - 1)].add(rule)
-            r1_tree = trees[span1][r1.lhs]
-            r2_tree = trees[span2][r2.lhs]
-            rule_total_weight = rule.weight + r1_tree.weight + r2_tree.weight
-            if (rule.lhs not in trees[(i, i + l - 1)] or
-                rule_total_weight < trees[(i, i + l - 1)][rule.lhs].weight):
-              trees[(i, i + l - 1)][rule.lhs] = RuleNode(rule, [r1_tree, r2_tree], weight=rule_total_weight)
-  return table, trees
+    if isinstance(node, RuleNode):
+        print(' ' * (indent * 2) + str(node.rule.lhs))
+        for child in node.children:
+            PrintParse(child, indent + 1)
+    else:
+        print(' ' * (indent * 2) + str(node.s))
+
+
+def _parse(s, g):
+    """Parses sentence 's' using CNF grammar 'g'."""
+    # The CYK table. Indexed with a 2-tuple: (start pos, end pos)
+    table = defaultdict(set)
+    # Top-level structure is similar to the CYK table. Each cell is a dict from
+    # rule name to the best (lightest) tree for that rule.
+    trees = defaultdict(dict)
+    # Populate base case with existing terminal production rules
+    for i, w in enumerate(s):
+        for terminal, rules in g.terminal_rules.items():
+            if terminal.match(w):
+                for rule in rules:
+                    table[(i, i)].add(rule)
+                    if (rule.lhs not in trees[(i, i)] or
+                        rule.weight < trees[(i, i)][rule.lhs].weight):
+                        trees[(i, i)][rule.lhs] = RuleNode(rule, [T(w)], weight=rule.weight)
+
+    # Iterate over lengths of sub-sentences
+    for l in xrange(2, len(s) + 1):
+        # Iterate over sub-sentences with the given length
+        for i in xrange(len(s) - l + 1):
+            # Choose partition of the sub-sentence in [1, l)
+            for p in xrange(i + 1, i + l):
+                span1 = (i, p - 1)
+                span2 = (p, i + l - 1)
+                for r1, r2 in itertools.product(table[span1], table[span2]):
+                    for rule in g.nonterminal_rules.get((r1.lhs, r2.lhs), []):
+                        table[(i, i + l - 1)].add(rule)
+                        r1_tree = trees[span1][r1.lhs]
+                        r2_tree = trees[span2][r2.lhs]
+                        rule_total_weight = rule.weight + r1_tree.weight + r2_tree.weight
+                        if (rule.lhs not in trees[(i, i + l - 1)]
+                            or rule_total_weight < trees[(i, i + l - 1)][rule.lhs].weight):
+                            trees[(i, i + l - 1)][rule.lhs] = RuleNode(rule, [r1_tree, r2_tree], weight=rule_total_weight)
+    return table, trees
 
 
 # This section implements context-free grammar converter to Chomsky normal form.
@@ -237,165 +205,162 @@ def _Parse(s, g):
 
 
 class CnfWrapper(object):
-  """CNF wrapper for grammar.
+    """CNF wrapper for grammar.
 
   Validates that the input grammar is CNF and provides helper data structures.
   """
 
-  def __init__(self, grammar):
-    super(CnfWrapper, self).__init__()
-    self.grammar = grammar
-    self.rules = grammar.rules
-    self.terminal_rules = defaultdict(list)
-    self.nonterminal_rules = defaultdict(list)
-    for r in self.rules:
-      # Validate that the grammar is CNF and populate auxiliary data structures.
-      assert isinstance(r.lhs, NT), r
-      assert len(r.rhs) in [1, 2], r
-      if len(r.rhs) == 1 and isinstance(r.rhs[0], T):
-        self.terminal_rules[r.rhs[0]].append(r)
-      elif len(r.rhs) == 2 and all(isinstance(x, NT) for x in r.rhs):
-        self.nonterminal_rules[tuple(r.rhs)].append(r)
-      else:
-        assert False, r
-
-  def __eq__(self, other):
-    return self.grammar == other.grammar
-
-  def __repr__(self):
-    return self.grammar.__repr__()
+    def __init__(self, grammar):
+        super(CnfWrapper, self).__init__()
+        self.grammar = grammar
+        self.rules = grammar.rules
+        self.terminal_rules = defaultdict(list)
+        self.nonterminal_rules = defaultdict(list)
+        for r in self.rules:
+            # Validate that the grammar is CNF and populate auxiliary data structures.
+            assert isinstance(r.lhs, NT), r
+            assert len(r.rhs) in [1, 2], r
+            if len(r.rhs) == 1 and isinstance(r.rhs[0], T):
+                self.terminal_rules[r.rhs[0]].append(r)
+            elif len(r.rhs) == 2 and all(isinstance(x, NT) for x in r.rhs):
+                self.nonterminal_rules[tuple(r.rhs)].append(r)
+            else:
+                assert False, r
+
+    def __eq__(self, other):
+        return self.grammar == other.grammar
+
+    def __repr__(self):
+        return repr(self.grammar)
 
 
 class UnitSkipRule(Rule):
-  """A rule that records NTs that were skipped during transformation."""
+    """A rule that records NTs that were skipped during transformation."""
 
-  def __init__(self, lhs, rhs, skipped_rules, weight, alias):
-    super(UnitSkipRule, self).__init__(lhs, rhs, weight, alias)
-    self.skipped_rules = skipped_rules
+    def __init__(self, lhs, rhs, skipped_rules, weight, alias):
+        super(UnitSkipRule, self).__init__(lhs, rhs, weight, alias)
+        self.skipped_rules = skipped_rules
 
-  def __eq__(self, other):
-    return (super(UnitSkipRule, self).__eq__(other) and
-            isinstance(other, type(self)) and
-            self.skipped_rules == other.skipped_rules)
+    def __eq__(self, other):
+        return isinstance(other, type(self)) and self.skipped_rules == other.skipped_rules
+
+    __hash__ = Rule.__hash__
 
 
 def BuildUnitSkipRule(unit_rule, target_rule):
-  skipped_rules = []
-  if isinstance(unit_rule, UnitSkipRule):
-    skipped_rules += unit_rule.skipped_rules
-  skipped_rules.append(target_rule)
-  if isinstance(target_rule, UnitSkipRule):
-    skipped_rules += target_rule.skipped_rules
-  return UnitSkipRule(unit_rule.lhs, target_rule.rhs, skipped_rules,
+    skipped_rules = []
+    if isinstance(unit_rule, UnitSkipRule):
+        skipped_rules += unit_rule.skipped_rules
+    skipped_rules.append(target_rule)
+    if isinstance(target_rule, UnitSkipRule):
+        skipped_rules += target_rule.skipped_rules
+    return UnitSkipRule(unit_rule.lhs, target_rule.rhs, skipped_rules,
                       weight=unit_rule.weight + target_rule.weight, alias=unit_rule.alias)
 
 
 def GetAnyNtUnitRule(g):
-  """Returns a non-terminal unit rule from 'g', or None if there is none."""
-  for rule in g.rules:
-    if len(rule.rhs) == 1 and isinstance(rule.rhs[0], NT):
-      return rule
-  return None
+    """Returns a non-terminal unit rule from 'g', or None if there is none."""
+    for rule in g.rules:
+        if len(rule.rhs) == 1 and isinstance(rule.rhs[0], NT):
+            return rule
+    return None
 
 
 def RemoveUnitRule(g, rule):
-  """Removes 'rule' from 'g' without changing the langugage produced by 'g'."""
-  new_rules = [x for x in g.rules if x != rule]
-  refs = [x for x in g.rules if x.lhs == rule.rhs[0]]
-  for ref in refs:
-    new_rules.append(BuildUnitSkipRule(rule, ref))
-  return Grammar(new_rules)
+    """Removes 'rule' from 'g' without changing the langugage produced by 'g'."""
+    new_rules = [x for x in g.rules if x != rule]
+    refs = [x for x in g.rules if x.lhs == rule.rhs[0]]
+    for ref in refs:
+        new_rules.append(BuildUnitSkipRule(rule, ref))
+    return Grammar(new_rules)
 
 
 def Split(rule):
-  """Splits a rule whose len(rhs) > 2 into shorter rules."""
-  # if len(rule.rhs) <= 2:
-  #   return [rule]
-  rule_str = str(rule.lhs) + '__' + '_'.join(str(x) for x in rule.rhs)
-  rule_name = '__SP_%s' % (rule_str) + '_%d'
-  new_rules = [Rule(rule.lhs, [rule.rhs[0], NT(rule_name % 1)], weight=rule.weight, alias=rule.alias)]
-  for i in xrange(1, len(rule.rhs) - 2):
-    new_rules.append(
-        Rule(NT(rule_name % i),
-             [rule.rhs[i], NT(rule_name % (i + 1))], weight=0, alias='Split'))
-  new_rules.append(Rule(NT(rule_name % (len(rule.rhs) - 2)), rule.rhs[-2:], weight=0, alias='Split'))
-  return new_rules
+    """Splits a rule whose len(rhs) > 2 into shorter rules."""
+    rule_str = str(rule.lhs) + '__' + '_'.join(str(x) for x in rule.rhs)
+    rule_name = '__SP_%s' % (rule_str) + '_%d'
+    new_rules = [Rule(rule.lhs, [rule.rhs[0], NT(rule_name % 1)], weight=rule.weight, alias=rule.alias)]
+    for i in xrange(1, len(rule.rhs) - 2):
+        new_rules.append( Rule(NT(rule_name % i),
+                         [rule.rhs[i], NT(rule_name % (i + 1))], weight=0, alias='Split'))
+    new_rules.append(Rule(NT(rule_name % (len(rule.rhs) - 2)), rule.rhs[-2:], weight=0, alias='Split'))
+    return new_rules
 
 
 def Term(g):
-  """Applies the TERM rule on 'g' (see top comment)."""
-  all_t = {x for rule in g.rules for x in rule.rhs if isinstance(x, T)}
-  t_rules = {t: Rule(NT('__T_%s' % str(t)), [t], weight=0, alias='Term') for t in all_t}
-  new_rules = []
-  for rule in g.rules:
-    if len(rule.rhs) > 1 and any(isinstance(x, T) for x in rule.rhs):
-      new_rhs = [t_rules[x].lhs if isinstance(x, T) else x for x in rule.rhs]
-      new_rules.append(Rule(rule.lhs, new_rhs, weight=rule.weight, alias=rule.alias))
-      new_rules.extend(v for k, v in t_rules.iteritems() if k in rule.rhs)
-    else:
-      new_rules.append(rule)
-  return Grammar(new_rules)
+    """Applies the TERM rule on 'g' (see top comment)."""
+    all_t = {x for rule in g.rules for x in rule.rhs if isinstance(x, T)}
+    t_rules = {t: Rule(NT('__T_%s' % str(t)), [t], weight=0, alias='Term') for t in all_t}
+    new_rules = []
+    for rule in g.rules:
+        if len(rule.rhs) > 1 and any(isinstance(x, T) for x in rule.rhs):
+            new_rhs = [t_rules[x].lhs if isinstance(x, T) else x for x in rule.rhs]
+            new_rules.append(Rule(rule.lhs, new_rhs, weight=rule.weight, alias=rule.alias))
+            new_rules.extend(v for k, v in t_rules.items() if k in rule.rhs)
+        else:
+            new_rules.append(rule)
+    return Grammar(new_rules)
 
 
 def Bin(g):
-  """Applies the BIN rule to 'g' (see top comment)."""
-  new_rules = []
-  for rule in g.rules:
-    if len(rule.rhs) > 2:
-      new_rules.extend(Split(rule))
-    else:
-      new_rules.append(rule)
-  return Grammar(new_rules)
+    """Applies the BIN rule to 'g' (see top comment)."""
+    new_rules = []
+    for rule in g.rules:
+        if len(rule.rhs) > 2:
+            new_rules.extend(Split(rule))
+        else:
+            new_rules.append(rule)
+    return Grammar(new_rules)
 
 
 def Unit(g):
-  """Applies the UNIT rule to 'g' (see top comment)."""
-  nt_unit_rule = GetAnyNtUnitRule(g)
-  while nt_unit_rule:
-    g = RemoveUnitRule(g, nt_unit_rule)
+    """Applies the UNIT rule to 'g' (see top comment)."""
     nt_unit_rule = GetAnyNtUnitRule(g)
-  return g
+    while nt_unit_rule:
+        g = RemoveUnitRule(g, nt_unit_rule)
+        nt_unit_rule = GetAnyNtUnitRule(g)
+    return g
 
 
 def ToCnf(g):
-  """Creates a CNF grammar from a general context-free grammar 'g'."""
-  g = Unit(Bin(Term(g)))
-  return CnfWrapper(g)
+    """Creates a CNF grammar from a general context-free grammar 'g'."""
+    g = Unit(Bin(Term(g)))
+    return CnfWrapper(g)
 
 
 def UnrollUnitSkipRule(lhs, orig_rhs, skipped_rules, children, weight, alias):
-  if not skipped_rules:
-    return RuleNode(Rule(lhs, orig_rhs, weight=weight, alias=alias), children, weight=weight)
-  else:
-    weight = weight - skipped_rules[0].weight
-    return RuleNode(
-        Rule(lhs, [skipped_rules[0].lhs], weight=weight, alias=alias), [
-            UnrollUnitSkipRule(skipped_rules[0].lhs, orig_rhs,
-                               skipped_rules[1:], children,
-                               skipped_rules[0].weight, skipped_rules[0].alias)
-        ], weight=weight)
+    if not skipped_rules:
+        return RuleNode(Rule(lhs, orig_rhs, weight=weight, alias=alias), children, weight=weight)
+    else:
+        weight = weight - skipped_rules[0].weight
+        return RuleNode(
+            Rule(lhs, [skipped_rules[0].lhs], weight=weight, alias=alias), [
+                UnrollUnitSkipRule(skipped_rules[0].lhs, orig_rhs,
+                                skipped_rules[1:], children,
+                                skipped_rules[0].weight, skipped_rules[0].alias)
+            ], weight=weight)
 
 
 def RevertCnf(node):
-  """Reverts a parse tree (RuleNode) to its original non-CNF form (Node)."""
-  if isinstance(node, T):
-    return node
-  # Reverts TERM rule.
-  if node.rule.lhs.s.startswith('__T_'):
-    return node.children[0]
-  else:
-    children = []
-    reverted_children = [RevertCnf(x) for x in node.children]
-    for child in reverted_children:
-      # Reverts BIN rule.
-      if isinstance(child, RuleNode) and child.rule.lhs.s.startswith('__SP_'):
-        children.extend(child.children)
-      else:
-        children.append(child)
-    # Reverts UNIT rule.
-    if isinstance(node.rule, UnitSkipRule):
-      return UnrollUnitSkipRule(node.rule.lhs, node.rule.rhs,
-                                node.rule.skipped_rules, children,
-                                node.rule.weight, node.rule.alias)
+    """Reverts a parse tree (RuleNode) to its original non-CNF form (Node)."""
+    if isinstance(node, T):
+        return node
+    # Reverts TERM rule.
+    if node.rule.lhs.s.startswith('__T_'):
+        return node.children[0]
     else:
-      return RuleNode(node.rule, children)
+        children = []
+        reverted_children = [RevertCnf(x) for x in node.children]
+        for child in reverted_children:
+            # Reverts BIN rule.
+            if isinstance(child, RuleNode) and child.rule.lhs.s.startswith('__SP_'):
+                children.extend(child.children)
+            else:
+                children.append(child)
+        # Reverts UNIT rule.
+        if isinstance(node.rule, UnitSkipRule):
+            return UnrollUnitSkipRule(node.rule.lhs, node.rule.rhs,
+                                    node.rule.skipped_rules, children,
+                                    node.rule.weight, node.rule.alias)
+        else:
+            return RuleNode(node.rule, children)

tests/__main__.py

@@ -16,6 +16,7 @@ except ImportError:
 from .test_parser import (
         TestLalrStandard,
         TestEarleyStandard,
+        TestCykStandard,
         TestLalrContextual,
         TestEarleyScanless,
         TestEarleyDynamic,

tests/test_parser.py

@@ -382,6 +382,7 @@ def _make_parser_test(LEXER, PARSER):
             g.parse(u'\xa3\u0101\u00a3\u0203\n')
 
 
+        @unittest.skipIf(PARSER == 'cyk', "Takes forever")
         def test_stack_for_ebnf(self):
             """Verify that stack depth isn't an issue for EBNF grammars"""
             g = _Lark(r"""start: a+
@@ -455,6 +456,7 @@ def _make_parser_test(LEXER, PARSER):
 
 
 
+        @unittest.skipIf(PARSER == 'cyk', "No empty rules")
         def test_empty_expand1_list(self):
             g = _Lark(r"""start: list
                             ?list: item*
@@ -473,6 +475,7 @@ def _make_parser_test(LEXER, PARSER):
             [list] = r.children
             self.assertSequenceEqual([item.data for item in list.children], ())
 
+        @unittest.skipIf(PARSER == 'cyk', "No empty rules")
         def test_empty_expand1_list_2(self):
             g = _Lark(r"""start: list
                             ?list: item* "!"?
@@ -492,6 +495,7 @@ def _make_parser_test(LEXER, PARSER):
             self.assertSequenceEqual([item.data for item in list.children], ())
 
 
+        @unittest.skipIf(PARSER == 'cyk', "No empty rules")
         def test_empty_flatten_list(self):
             g = _Lark(r"""start: list
                             list: | item "," list
@@ -645,6 +649,7 @@ def _make_parser_test(LEXER, PARSER):
             self.assertEqual(len(x.children), 1, '/a/ should not be considered anonymous')
             self.assertEqual(x.children[0].type, "A")
 
+        @unittest.skipIf(PARSER == 'cyk', "No empty rules")
         def test_maybe(self):
             g = _Lark("""start: ["a"] """)
             x = g.parse('a')
@@ -702,6 +707,7 @@ def _make_parser_test(LEXER, PARSER):
         #                  B: A
         #               """)
 
+        @unittest.skipIf(PARSER == 'cyk', "No empty rules")
         def test_empty(self):
             # Fails an Earley implementation without special handling for empty rules,
             # or re-processing of already completed rules.
@@ -732,6 +738,8 @@ def _make_parser_test(LEXER, PARSER):
 
         def test_float_without_lexer(self):
             expected_error = UnexpectedInput if LEXER == 'dynamic' else UnexpectedToken
+            if PARSER == 'cyk':
+                expected_error = ParseError
 
             g = _Lark("""start: ["+"|"-"] float
                          float: digit* "." digit+ exp?
@@ -796,6 +804,7 @@ def _make_parser_test(LEXER, PARSER):
             self.assertEqual(tree.children, ['a', 'A'])
 
 
+        @unittest.skipIf(PARSER == 'cyk', "No empty rules")
         def test_twice_empty(self):
             g = """!start: [["A"]]
                 """
@@ -1001,6 +1010,7 @@ def _make_parser_test(LEXER, PARSER):
 
 
         @unittest.skipIf(LEXER==None, "Scanless doesn't support regular expressions")
+        @unittest.skipIf(PARSER == 'cyk', "No empty rules")
         def test_ignore(self):
             grammar = r"""
             COMMENT: /(!|(\/\/))[^\n]*/
@@ -1026,7 +1036,6 @@ def _make_parser_test(LEXER, PARSER):
             self.assertEqual(tree.children, [])
 
 
-
         @unittest.skipIf(LEXER==None, "Scanless doesn't support regular expressions")
         def test_regex_escaping(self):
             g = _Lark("start: /[ab]/")
@@ -1075,6 +1084,7 @@ def _make_parser_test(LEXER, PARSER):
 # Note: You still have to import them in __main__ for the tests to run
 _TO_TEST = [
         ('standard', 'earley'),
+        ('standard', 'cyk'),
         ('dynamic', 'earley'),
         ('standard', 'lalr'),
         ('contextual', 'lalr'),