Detect predicates used in DCG clauses

1 files changed, 11 insertions, 2 deletions

diff --git a/prolog/util.py b/prolog/util.py
index 83f891f..e1ce36b 100644
--- a/prolog/util.py
+++ b/prolog/util.py
@@ -196,8 +196,12 @@ def map_vars(a, b, tokens, variables):
 # Return a set of predicate names (e.g. conc/3) used in [program].
 def used_predicates(program):
     predicates = set()
-    def walk(tree):
+    def walk(tree, dcg=False):
         if isinstance(tree, Tree):
+            # DCG predicates can be called without parameters
+            if tree.label() == 'clause' and len(tree) == 4 and \
+                    tree[1].type == 'FROMDCG':
+                dcg = True
             if tree.label() == 'term' and len(tree) >= 3 and \
                     isinstance(tree[0], Tree) and tree[0].label() == 'functor':
                 if len(tree) == 3:
@@ -205,7 +209,12 @@ def used_predicates(program):
                 else:
                     predicates.add('{}/{}'.format(tree[0][0], (len(tree[2])+1)//2))
             for subtree in tree:
-                walk(subtree)
+                walk(subtree, dcg)
+        elif isinstance(tree, Token):
+            if dcg and tree.type == 'NAME':
+                predicates.add('{}/{}'.format(tree.val, 2))
+                predicates.add('{}/{}'.format(tree.val, 3))
+                predicates.add('{}/{}'.format(tree.val, 4))
     tree = parse(program)
     if tree is not None:
         walk(tree)