add, implement and use the Unifier trait, use it to improve dif:attri…

…bute_goals//2 (#1382, #1433)

Cargo.toml

@@ -63,6 +63,7 @@ hyper = { version = "0.14", features = ["full"] }
 hyper-tls = "0.5.0"
 tokio = { version = "1.24.2", features = ["full"] }
 futures = "0.3"
+derive_deref = "1.1.1"
 
 [dev-dependencies]
 assert_cmd = "1.0.3"

build/instructions_template.rs

@@ -568,6 +568,8 @@ enum SystemClauseType {
     DeleteFromAttributedVarList,
     #[strum_discriminants(strum(props(Arity = "1", Name = "$delete_all_attributes_from_var")))]
     DeleteAllAttributesFromVar,
+    #[strum_discriminants(strum(props(Arity = "2", Name = "$terms_unify")))]
+    TermsUnify,
     REPL(REPLCodePtr),
 }
 
@@ -1630,6 +1632,7 @@ fn generate_instruction_preface() -> TokenStream {
                     &Instruction::CallPutToAttributedVarList(_) |
                     &Instruction::CallDeleteFromAttributedVarList(_) |
                     &Instruction::CallDeleteAllAttributesFromVar(_) |
+                    &Instruction::CallTermsUnify(_) |
                     &Instruction::CallFetchGlobalVar(_) |
                     &Instruction::CallFirstStream(_) |
                     &Instruction::CallFlushOutput(_) |
@@ -1846,6 +1849,7 @@ fn generate_instruction_preface() -> TokenStream {
                     &Instruction::ExecutePutToAttributedVarList(_) |
                     &Instruction::ExecuteDeleteFromAttributedVarList(_) |
                     &Instruction::ExecuteDeleteAllAttributesFromVar(_) |
+                    &Instruction::ExecuteTermsUnify(_) |
                     &Instruction::ExecuteFetchGlobalVar(_) |
                     &Instruction::ExecuteFirstStream(_) |
                     &Instruction::ExecuteFlushOutput(_) |

src/lib/dif.pl

@@ -23,13 +23,22 @@
     put_dif_att(Var, X, Y),
     dif_set_variables(Vars, X, Y).
 
+filter_non_unifiable_goals([]) --> [].
+filter_non_unifiable_goals([(X \== Y)|Goals]) -->
+    (   { '$terms_unify'(X, Y) } ->
+        [(X \== Y)]
+    ;   []
+    ),
+    filter_non_unifiable_goals(Goals).
+
 append_goals([], _).
 append_goals([Var|Vars], Goals) :-
     (   get_atts(Var, +dif(VarGoals)) ->
 	    append(Goals, VarGoals, NewGoals0),
-	    sort(NewGoals0, NewGoals)
-    ;   NewGoals = Goals
+	    sort(NewGoals0, NewGoals1)
+    ;   NewGoals1 = Goals
     ),
+    phrase(filter_non_unifiable_goals(NewGoals1), NewGoals),
     put_atts(Var, +dif(NewGoals)),
     append_goals(Vars, Goals).
 
@@ -68,7 +77,8 @@
 
 gather_dif_goals(_, []) --> [].
 gather_dif_goals(V, [(X \== Y) | Goals]) -->
-    (  { term_variables(X, [V0 | _]),
+    (  { '$terms_unify'(X,Y),
+         term_variables(X, [V0 | _]),
          V == V0 } ->
        [dif:dif(X, Y)]
     ;  []

src/machine/dispatch.rs

@@ -5215,6 +5215,14 @@ impl Machine {
                     self.delete_all_attributes_from_var();
                     self.machine_st.p = self.machine_st.cp;
                 }
+                &Instruction::CallTermsUnify(_) => {
+                    self.terms_unify();
+                    step_or_fail!(self, self.machine_st.p += 1);
+                }
+                &Instruction::ExecuteTermsUnify(_) => {
+                    self.terms_unify();
+                    step_or_fail!(self, self.machine_st.p = self.machine_st.cp);
+                }
             }
         }