Add forest.get_first_tree() for unpacking tree 0

Author: igordejanovic

docs/parse_forest_trees.md

@@ -63,6 +63,12 @@ string/dot.
         
     For smaller inputs you can also use `to_dot` to display a forest/tree as a graph.
 
+There is also `forest.get_tree(idx)` which is the same as `forest[idx]`, i.e. it
+returns lazy tree. To get non-lazy tree, i.e. tree whose proxies are
+pre-initialized, call `forest.get_nonlazy_tree(idx)`. If you just need the first
+tree, call `forest.get_first_tree()` to get an unpacked tree which consists only
+of `NodeTerm` and `NodeNonTerm`. This tree is the fastest to navigate but only
+tree 0 is supported in this form.
 
 # Parse trees
 

parglare/trees.py

@@ -292,6 +292,32 @@ def get_tree(self, idx=0):
     def get_nonlazy_tree(self, idx=0):
         return Tree(self.result, idx)
 
+    def get_first_tree(self):
+        """
+        Gets tree 0 fully unpacked. May be used for optimization purposes where
+        it doesn't matter which tree we get. The unpacked tree is faster to iterate.
+        """
+        from parglare.glr import Parent
+
+        def tree_iterator(n):
+            if isinstance(n, Parent):
+                return iter([n.possibilities[0]])
+            elif n.is_nonterm():
+                return iter(n.children)
+            else:
+                return iter([])
+
+        def visit(n, subresults):
+            if isinstance(n, Parent):
+                return subresults[0]
+            elif n.is_nonterm():
+                # Clone NodeNonTerm to preserve the forest
+                return NodeNonTerm(n.context, subresults, n.production)
+            else:
+                return n
+
+        return visitor(self.result.possibilities[0], tree_iterator, visit)
+
     @property
     def solutions(self):
         return self.result.solutions

tests/func/parsing/test_glr_forest.py

@@ -185,3 +185,11 @@ def test_multiple_iteration(parser):
 
     for tree in forest.nonlazy_iter():
         assert tree.to_str() == tree.to_str()
+
+
+def test_get_first_tree(parser):
+    """
+    Test that unpacked tree is the same as lazy tree 0.
+    """
+    forest = parser.parse('2 + 3 * 5 + 4 * 1 * 7 + 9 + 10')
+    assert forest.get_first_tree().to_str() == forest[0].to_str()