Group clauses into predicates, and create all valid choicepoints at once. This is wastefull if one branch loops forever, but it is much nicer otherwise, since we know the choicepoints only gets created as long as their head is unifiable with the goal.

1 files changed, 75 insertions, 31 deletions

diff --git a/eval.c b/eval.c
index e0d7286..e42439f 100644
--- a/eval.c
+++ b/eval.c
@@ -6,10 +6,12 @@
 #include "fns.h"
 
 Goal *addgoals(Goal *, Term *);
+Predicate *findpredicate(Predicate *, Term *);
 Clause *findclause(Clause *, Term *, Binding **);
 int equalterms(Term *, Term *);
 Goal *copygoals(Goal *);
 Builtin findbuiltin(Term *);
+void addchoicepoints(Clause *, Term *, Goal *, Module *);
 
 static uvlong clausenr;
 
@@ -45,23 +47,17 @@ evalquery(Term *query, Binding **resultbindings)
 	}
 
 	while(goalstack->goal != nil){
-		Clause *startclause;
-		Term *goal;
-		Goal *oldgoalstack;
-
-		startclause = nil; /* Where to start looking for a matching clause. Used by backtracking */
-Retry:
-		goal = goalstack->goal;
-		oldgoalstack = goalstack;
+		Term *goal = goalstack->goal;
+		Term *catcher = goalstack->catcher;
 		goalstack = goalstack->next;
 
-		if(oldgoalstack->catcher)
+		if(catcher)
 			continue;
 
 		if(debug)
 			print("Working goal: %S\n", prettyprint(goal, 0, 0, 0));
 
-		if(startclause == nil && goal->tag == CompoundTerm && goal->arity == 2 && runestrcmp(goal->text, L":") == 0){
+		if(goal->tag == CompoundTerm && goal->arity == 2 && runestrcmp(goal->text, L":") == 0){
 			Term *module = goal->children;
 			if(module->tag == AtomTerm){
 				Module *m = getmodule(module->text);
@@ -70,16 +66,11 @@ Retry:
 				else{
 					goal = module->next;
 					currentmodule = m;
-					startclause = m->clauses;
-					oldgoalstack->goal = goal;
 				}
 			}else
 				goal = typeerror(L"module", module);
 		}
 
-		if(startclause == nil)
-			startclause = currentmodule->clauses;
-
 		Binding *bindings = nil;
 		Clause *clause = nil;
 		
@@ -90,20 +81,17 @@ Retry:
 			if(!success)
 				goto Backtrack;
 		}else{
+			Predicate *pred = findpredicate(currentmodule->predicates, goal);
+			if(pred == nil){
+				print("No predicate matches: %S\n", prettyprint(goal, 0, 0, 0));
+				goto Backtrack;
+			}
+
 			/* Find a clause where the head unifies with the goal */
-			clause = findclause(startclause, goal, &bindings);
-			if(clause != nil){
-				if(clause->next != nil){
-					/* Add a choicepoint. Note we create a choicepoint every time, so there is room for improvement. */
-					Choicepoint *cp = malloc(sizeof(Choicepoint));
-					cp->goalstack = copygoals(oldgoalstack);
-					cp->next = choicestack;
-					cp->retryclause = clause->next;
-					cp->id = clause->clausenr;
-					cp->currentmodule = currentmodule;
-					choicestack = cp;
-				}
-			}else{
+			clause = findclause(pred->clauses, goal, &bindings);
+			if(clause != nil)
+				addchoicepoints(clause, goal, goalstack, currentmodule);
+			else{
 Backtrack:
 				if(choicestack == nil)
 					return 0;
@@ -111,11 +99,10 @@ Backtrack:
 					print("Backtracking..\n");
 				Choicepoint *cp = choicestack;
 				choicestack = cp->next;
-				/* freegoals(goals) */
 				goalstack = cp->goalstack;
 				currentmodule = cp->currentmodule;
-				startclause = cp->retryclause;
-				goto Retry;
+				clause = cp->alternative;
+				bindings = cp->altbindings;
 			}
 		}
 
@@ -171,6 +158,26 @@ findclause(Clause *clauses, Term *goal, Binding **bindings)
 	return nil;
 }
 
+Predicate *
+findpredicate(Predicate *preds, Term *goal)
+{
+	Rune *name;
+	int arity;
+
+	name = goal->text;
+	if(goal->tag == AtomTerm)
+		arity = 0;
+	else
+		arity = goal->arity;
+
+	Predicate *p;
+	for(p = preds; p != nil; p = p->next){
+		if(runestrcmp(p->name, name) == 0 && p->arity == arity)
+			return p;
+	}
+	return nil;
+}
+
 int
 unify(Term *a, Term *b, Binding **bindings)
 {
@@ -293,3 +300,40 @@ copygoals(Goal *goals)
 	}else
 		return nil;
 }
+
+void
+addchoicepoints(Clause *clause, Term *goal, Goal *goals, Module *mod){
+	/* Find all alternative clauses that would have matched, and create a choicepoint for them */
+	Choicepoint *cps = nil;
+	Choicepoint *last = nil;
+
+	Clause *alt = clause->next;
+	while(alt != nil){
+		Binding *altbindings = nil;
+		clause = findclause(alt, goal, &altbindings);
+		if(clause){
+			/* Add choicepoint here */
+			Choicepoint *cp = malloc(sizeof(Choicepoint));
+			cp->goalstack = copygoals(goals);
+			cp->next = nil;
+			cp->alternative = clause;
+			cp->altbindings = altbindings;
+			cp->id = clause->clausenr;
+			cp->currentmodule = mod;
+			if(cps == nil){
+				cps = cp;
+				last = cp;
+			}else{
+				last->next = cp;
+				last = cp;
+			}
+			alt = clause->next;
+		}else
+			alt = nil;
+	}
+
+	if(last){
+		last->next = choicestack;
+		choicestack = cps;
+	}
+}
\ No newline at end of file