Option to call semantic actions while building parse tree

docs/parser.md

@@ -38,6 +38,18 @@ used instead and this parameter is ignored.
 A boolean whose default value is `False`. If set to `True` parser will call
 actions that will build the [parse tree](./parse_trees.md).
 
+## call_actions_during_tree_build
+
+By default, this parameter is set to `False`. If set to `True`, parser will call
+actions during the parse tree [parse tree](./parse_trees.md) building process.
+The return value of each action will be discarded, since they directly affect
+the parse tree building process.
+
+!!! note
+
+    Use this parameter with a special care when GLR is used, since actions will
+    be called even on trees that can't be completed (unsuccessful parses).
+
 ## prefer_shifts
 
 By default set to `True` for LR parser and to `False` for GLR parser. In case

parglare/glr.py

@@ -33,10 +33,10 @@ class GLRParser(Parser):
     def __init__(self, grammar, start_production=1, actions=None,
                  layout_actions=None, debug=False, debug_trace=False,
                  debug_colors=False, debug_layout=False, ws='\n\t ',
-                 build_tree=False, tables=LALR, layout=False, position=False,
-                 prefer_shifts=None, prefer_shifts_over_empty=None,
-                 error_recovery=False, dynamic_filter=None,
-                 custom_lexical_disambiguation=None):
+                 build_tree=False, call_actions_during_tree_build=False,
+                 tables=LALR, layout=False, position=False, prefer_shifts=None,
+                 prefer_shifts_over_empty=None, error_recovery=False,
+                 dynamic_filter=None, custom_lexical_disambiguation=None):
 
         # The default for GLR is not to use any strategy preferring shifts
         # over reduce thus investigating all possibilitites.
@@ -50,8 +50,10 @@ def __init__(self, grammar, start_production=1, actions=None,
             actions=actions, layout_actions=layout_actions,
             debug=debug, debug_trace=debug_trace,
             debug_colors=debug_colors, debug_layout=debug_layout, ws=ws,
-            build_tree=build_tree, tables=tables, layout=layout,
-            position=position, prefer_shifts=prefer_shifts,
+            build_tree=build_tree,
+            call_actions_during_tree_build=call_actions_during_tree_build,
+            tables=tables, layout=layout, position=position,
+            prefer_shifts=prefer_shifts,
             prefer_shifts_over_empty=prefer_shifts_over_empty,
             error_recovery=error_recovery, dynamic_filter=dynamic_filter,
             custom_lexical_disambiguation=custom_lexical_disambiguation)

parglare/parser.py

@@ -26,10 +26,10 @@ class Parser(object):
     def __init__(self, grammar, start_production=1, actions=None,
                  layout_actions=None, debug=False, debug_trace=False,
                  debug_colors=False, debug_layout=False, ws='\n\r\t ',
-                 build_tree=False, tables=LALR, layout=False, position=False,
-                 prefer_shifts=True, prefer_shifts_over_empty=True,
-                 error_recovery=False, dynamic_filter=None,
-                 custom_lexical_disambiguation=None):
+                 build_tree=False, call_actions_during_tree_build=False,
+                 tables=LALR, layout=False, position=False, prefer_shifts=True,
+                 prefer_shifts_over_empty=True, error_recovery=False,
+                 dynamic_filter=None, custom_lexical_disambiguation=None):
         self.grammar = grammar
         self.start_production = start_production
         EMPTY.action = pass_none
@@ -62,6 +62,7 @@ def __init__(self, grammar, start_production=1, actions=None,
         self.debug_layout = debug_layout
 
         self.build_tree = build_tree
+        self.call_actions_during_tree_build = call_actions_during_tree_build
 
         self.error_recovery = error_recovery
         self.dynamic_filter = dynamic_filter
@@ -545,12 +546,21 @@ def _call_shift_action(self, symbol, matched_str, context):
         Calls registered shift action for the given grammar symbol.
         """
         debug = self.debug
+        sem_action = symbol.action
 
         if self.build_tree:
             # call action for building tree node if tree building is enabled
             if debug:
                 h_print("Building terminal node",
                         "'{}'.".format(symbol.name), level=2)
+
+            # If both build_tree and call_actions_during_build are set to
+            # True, semantic actions will be call but their result will be
+            # discarded. For more info check following issue:
+            # https://github.com/igordejanovic/parglare/issues/44
+            if self.call_actions_during_tree_build and sem_action:
+                sem_action(context, matched_str)
+
             return treebuild_shift_action(context, matched_str)
 
         sem_action = symbol.action
@@ -578,13 +588,17 @@ def _call_reduce_action(self, production, subresults, context):
         """
         debug = self.debug
         result = None
+        bt_result = None
 
         if self.build_tree:
             # call action for building tree node if enabled.
             if debug:
                 h_print("Building non-terminal node",
                         "'{}'.".format(production.symbol.name), level=2)
-            return treebuild_reduce_action(context, nodes=subresults)
+
+            bt_result = treebuild_reduce_action(context, nodes=subresults)
+            if not self.call_actions_during_tree_build:
+                return bt_result
 
         sem_action = production.symbol.action
         if sem_action:
@@ -628,7 +642,9 @@ def _call_reduce_action(self, production, subresults, context):
                     "type:{} value:{}"
                     .format(type(result), repr(result)), level=1)
 
-        return result
+        # If build_tree is set to True, discard the result of the semantic
+        # action, and return the result of treebuild_reduce_action.
+        return bt_result if bt_result is not None else result
 
     def _lexical_disambiguation(self, tokens):
         """

tests/func/test_build_tree.py

@@ -0,0 +1,42 @@
+import pytest  # noqa
+from parglare import Grammar, Parser
+
+
+def test_call_actions_during_tree_build():
+    grammar = """
+    Program: "begin" MoveCommand* "end";
+    MoveCommand: "move" Direction;
+    Direction: "up" | "down" | "left" | "right";
+    """
+
+    g = Grammar.from_string(grammar)
+
+    code = """
+    begin
+        move left
+        move left
+        move up
+        move down
+    end
+    """
+
+    left_moves = []
+
+    def left_dir_collector(_, nodes):
+        """Finds all 'left' moves and adds them into a list."""
+        term = nodes[0]
+        if term.value == "left":
+            left_moves.append(term)
+
+    parser = Parser(g, build_tree=True,
+                    actions={"Direction": left_dir_collector})
+    parser.parse(code)
+
+    # call_actions_during_tree_build is False by default, so left_dir_collector
+    # will not be called.
+    assert len(left_moves) == 0
+
+    parser.call_actions_during_tree_build = True
+    parser.parse(code)
+
+    assert len(left_moves) == 2