Add support for builtins, and implement true/0, fail/0, call/1, and !/0 builtins

1 files changed, 46 insertions, 49 deletions

diff --git a/eval.c b/eval.c
index 8a372a3..cf26fdf 100644
--- a/eval.c
+++ b/eval.c
@@ -4,28 +4,13 @@
 #include "dat.h"
 #include "fns.h"
 
-typedef struct Goal Goal;
-typedef struct Choicepoint Choicepoint;
-
-struct Goal
-{
-	Term *goal;
-	Goal *next;
-};
-
-struct Choicepoint
-{
-	Goal *goalstack;
-	Term *retryclause;
-	Choicepoint *next;
-};
-
 Goal *addgoals(Goal *, Term *);
 Term *findclause(Term *, Term *, Binding **);
 int unify(Term *, Term *, Binding **);
 int equalterms(Term *, Term *);
 void applybinding(Term *, Binding *);
 Goal *copygoals(Goal *);
+Builtin findbuiltin(Term *);
 
 static uvlong clausenr;
 
@@ -63,43 +48,55 @@ evalquery(Term *database, Term *query, Binding **resultbindings)
 Retry:
 		goal = goals->goal;
 
-		/* Find a clause where the head unifies with the goal */
 		Binding *bindings = nil;
-		Term *clause = findclause(dbstart, 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(goals);
-				cp->next = choicestack;
-				cp->retryclause = clause->next;
-				choicestack = cp;
-			}
-			goals = goals->next;
+		Term *clause = nil;
 
-			/* Apply bindings to all goals on the stack. */
-			Goal *g;
-			for(g = goals; g != nil; g = g->next){
-				if(g->goal != nil)
-					applybinding(g->goal, bindings);
-			}
-			
-			/* Add clause body as goals, with bindings applied */
-			if(clause->tag == CompoundTerm && clause->arity == 2 && runestrcmp(clause->text, L":-") == 0){
-				Term *subgoal = copyterm(clause->children->next, nil);
-				applybinding(subgoal, bindings);
-				goals = addgoals(goals, subgoal);
-			}
+		/* Try to see if the goal can be solved using a builtin first */
+		Builtin builtin = findbuiltin(goal);
+		if(builtin != nil){
+			int success = builtin(database, goal, &goals->next, &choicestack, &bindings);
+			if(!success)
+				goto Backtrack;
 		}else{
-			if(choicestack == nil)
-				return 0;
-			Choicepoint *cp = choicestack;
-			choicestack = cp->next;
-			/* freegoals(goals) */
-			goals = cp->goalstack;
-			dbstart = cp->retryclause;
+			/* Find a clause where the head unifies with the goal */
+			clause = findclause(dbstart, 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(goals);
+					cp->next = choicestack;
+					cp->retryclause = clause->next;
+					cp->id = clause->clausenr;
+					choicestack = cp;
+				}
+			}else{
+Backtrack:
+				if(choicestack == nil)
+					return 0;
+				Choicepoint *cp = choicestack;
+				choicestack = cp->next;
+				/* freegoals(goals) */
+				goals = cp->goalstack;
+				dbstart = cp->retryclause;
+				goto Retry;
+			}
+		}
+		
+		goals = goals->next;
+
+		/* Apply bindings to all goals on the stack. */
+		Goal *g;
+		for(g = goals; g != nil; g = g->next){
+			if(g->goal != nil)
+				applybinding(g->goal, bindings);
+		}
 
-			goto Retry;
+		/* Add clause body as goals, with bindings applied */
+		if(clause != nil && clause->tag == CompoundTerm && clause->arity == 2 && runestrcmp(clause->text, L":-") == 0){
+			Term *subgoal = copyterm(clause->children->next, nil);
+			applybinding(subgoal, bindings);
+			goals = addgoals(goals, subgoal);
 		}
 	}
 	goals = goals->next;