From 90a7dec41ac4f68c4c9a99eb77ebf340a36e536e Mon Sep 17 00:00:00 2001
From: Jedidiah Barber <contact@jedbarber.id.au>
Date: Wed, 12 Nov 2025 14:33:11 +1300
Subject: Bugfixes in Unify and Term Image, query function for World failure

---
 src/kompsos.adb | 75 +++++++++++++++++++++++++++++++++++----------------------
 1 file changed, 46 insertions(+), 29 deletions(-)

(limited to 'src/kompsos.adb')

diff --git a/src/kompsos.adb b/src/kompsos.adb
index d018c27..3981005 100644
--- a/src/kompsos.adb
+++ b/src/kompsos.adb
@@ -235,7 +235,10 @@ package body Kompsos is
             Item : in Term'Class)
         return Term'Class is
     begin
-        if This.Subst.Contains (Item.Actual.Refer.Ident) then
+        if  Item.Actual /= null and then
+            Item.Actual.Kind = Var_Term and then
+            This.Subst.Contains (Item.Actual.Refer.Ident)
+        then
             return Walk (This, This.Subst.Constant_Reference (Item.Actual.Refer.Ident));
         else
             return Item;
@@ -268,24 +271,48 @@ package body Kompsos is
             end if;
         end if;
 
-        --  Check for null Terms
+        --  Check for equal null Terms
         if Real_Left.Actual = null and Real_Right.Actual = null then
             Extended := Potential;
             return True;
         end if;
-        if Real_Left.Actual = null or Real_Right.Actual = null then
-            return False;
-        end if;
 
         --  Unify equal Variable Terms
-        if  Real_Left.Actual.Kind = Var_Term and then
-            Real_Right.Actual.Kind = Var_Term and then
+        if  Real_Left.Actual /= null and then Real_Left.Actual.Kind = Var_Term and then
+            Real_Right.Actual /= null and then Real_Right.Actual.Kind = Var_Term and then
             Real_Left = Real_Right
         then
             Extended := Potential;
             return True;
         end if;
 
+        --  Unify Variable and other Terms by introducing a new substitution
+        if Real_Left.Actual /= null and then Real_Left.Actual.Kind = Var_Term then
+            if  Real_Right.Actual /= null and then Real_Right.Actual.Kind = Pair_Term and then
+                not Fully_Contains (Potential, Real_Right)
+            then
+                return False;
+            end if;
+            Extended := Potential;
+            Extended.Subst.Insert (Real_Left.Actual.Refer.Ident, Term (Real_Right));
+            return True;
+        end if;
+        if Real_Right.Actual /= null and then Real_Right.Actual.Kind = Var_Term then
+            if  Real_Left.Actual /= null and then Real_Left.Actual.Kind = Pair_Term and then
+                not Fully_Contains (Potential, Real_Left)
+            then
+                return False;
+            end if;
+            Extended := Potential;
+            Extended.Subst.Insert (Real_Right.Actual.Refer.Ident, Term (Real_Left));
+            return True;
+        end if;
+
+        --  Don't want any null terms beyond here
+        if Real_Left.Actual = null or Real_Right.Actual = null then
+            return False;
+        end if;
+
         --  Unify equal Atom Terms
         if  Real_Left.Actual.Kind = Atom_Term and then
             Real_Right.Actual.Kind = Atom_Term and then
@@ -311,28 +338,6 @@ package body Kompsos is
             end;
         end if;
 
-        --  Unify Variable and other Terms by introducing a new substitution
-        if Real_Left.Actual.Kind = Var_Term then
-            if  Real_Right.Actual.Kind = Pair_Term and then
-                not Fully_Contains (Potential, Real_Right)
-            then
-                return False;
-            end if;
-            Extended := Potential;
-            Extended.Subst.Insert (Real_Left.Actual.Refer.Ident, Term (Real_Right));
-            return True;
-        end if;
-        if Real_Right.Actual.Kind = Var_Term then
-            if  Real_Left.Actual.Kind = Pair_Term and then
-                not Fully_Contains (Potential, Real_Left)
-            then
-                return False;
-            end if;
-            Extended := Potential;
-            Extended.Subst.Insert (Real_Right.Actual.Refer.Ident, Term (Real_Left));
-            return True;
-        end if;
-
         --  Not sure how things get here, but if all else fails
         return False;
     end Do_Unify;
@@ -491,6 +496,18 @@ package body Kompsos is
     --  Public API Operations  --
     -----------------------------
 
+    --  Query  --
+
+    function Failed
+           (This : in out World)
+        return Boolean is
+    begin
+        return not This.Has_State (1);
+    end Failed;
+
+
+
+
     --  Fresh  --
 
     function Fresh
-- 
cgit