diff --git a/lark/parsers/earley_forest.py b/lark/parsers/earley_forest.py index 532dedf..630ea63 100644 --- a/lark/parsers/earley_forest.py +++ b/lark/parsers/earley_forest.py @@ -490,19 +490,22 @@ class ForestToParseTree(ForestTransformer): self.prioritizer = prioritizer self.resolve_ambiguity = resolve_ambiguity self._on_cycle_retreat = False + self._cycle_node = None + self._successful_visits = set() def on_cycle(self, node, path): logger.warning("Cycle encountered in the SPPF at node: %s. " "As infinite ambiguities cannot be represented in a tree, " "this family of derivations will be discarded.", node) - if self.resolve_ambiguity: - # TODO: choose a different path if cycle is encountered - logger.warning("At this time, using ambiguity resolution for SPPFs " - "with cycles may result in None being returned.") + self._cycle_node = node self._on_cycle_retreat = True def _check_cycle(self, node): if self._on_cycle_retreat: + if id(node) == id(self._cycle_node): + self._cycle_node = None + self._on_cycle_retreat = False + return raise Discard() def _collapse_ambig(self, children): @@ -531,11 +534,17 @@ class ForestToParseTree(ForestTransformer): raise Discard() def transform_symbol_node(self, node, data): + if id(node) not in self._successful_visits: + raise Discard() + self._successful_visits.remove(id(node)) self._check_cycle(node) data = self._collapse_ambig(data) return self._call_ambig_func(node, data) def transform_intermediate_node(self, node, data): + if id(node) not in self._successful_visits: + raise Discard() + self._successful_visits.remove(id(node)) self._check_cycle(node) if len(data) > 1: children = [self.tree_class('_inter', c) for c in data] @@ -544,6 +553,8 @@ class ForestToParseTree(ForestTransformer): def transform_packed_node(self, node, data): self._check_cycle(node) + if self.resolve_ambiguity and id(node.parent) in self._successful_visits: + raise Discard() children = [] assert len(data) <= 2 data = PackedData(node, data) @@ -559,21 +570,23 @@ class ForestToParseTree(ForestTransformer): return self._call_rule_func(node, children) def visit_symbol_node_in(self, node): - self._on_cycle_retreat = False super(ForestToParseTree, self).visit_symbol_node_in(node) + if self._on_cycle_retreat: + return if self.prioritizer and node.is_ambiguous and isinf(node.priority): self.prioritizer.visit(node) - if self.resolve_ambiguity: - return node.children[0] return node.children def visit_packed_node_in(self, node): self._on_cycle_retreat = False - return super(ForestToParseTree, self).visit_packed_node_in(node) + to_visit = super(ForestToParseTree, self).visit_packed_node_in(node) + if not self.resolve_ambiguity or id(node.parent) not in self._successful_visits: + return to_visit - def visit_token_node(self, node): - self._on_cycle_retreat = False - return super(ForestToParseTree, self).visit_token_node(node) + def visit_packed_node_out(self, node): + super(ForestToParseTree, self).visit_packed_node_out(node) + if not self._on_cycle_retreat: + self._successful_visits.add(id(node.parent)) def handles_ambiguity(func): """Decorator for methods of subclasses of ``TreeForestTransformer``.