Add a basic repl

1 files changed, 33 insertions, 34 deletions

diff --git a/eval.c b/eval.c
index c755cf5..f3a1e15 100644
--- a/eval.c
+++ b/eval.c
@@ -4,18 +4,9 @@
 #include "dat.h"
 #include "fns.h"
 
-typedef struct Binding Binding;
 typedef struct Goal Goal;
 typedef struct Choicepoint Choicepoint;
 
-struct Binding
-{
-	Rune *name;
-	uvlong nr; /* Unique number for each clause. Every time a clause is used, it gets a new number. */
-	Term *value;
-	Binding *next;
-};
-
 struct Goal
 {
 	Term *goal;
@@ -38,15 +29,33 @@ Goal *copygoals(Goal *);
 
 static uvlong clausenr;
 
-void
-evalquery(Term *database, Term *query)
+int
+evalquery(Term *database, Term *query, Binding **resultbindings)
 {
-	Goal *goals = addgoals(nil, query);
+	Goal *goals;
 	Choicepoint *choicestack = nil;
 
 	clausenr = 0;
 
-	while(goals != nil){
+	/*
+		The goal stack has the original query at the very bottom, protected by a goal there the ->goal field is nil.
+		This makes it so that we can continue until we hit the protective goal, at which point we have solved everything
+		and to get the result we can unify the original query with the one at the bottom of the stack, to get the bindings
+		applied.
+	*/
+
+	goals = malloc(sizeof(Goal));
+	goals->goal = copyterm(query, nil);
+	goals->next = nil;
+	Goal *protector = malloc(sizeof(Goal));
+	protector->goal = nil;
+	protector->next = goals;
+	goals = protector;
+
+	/* Now add the actual goals */
+	goals = addgoals(goals, query);
+
+	while(goals->goal != nil){
 		Term *dbstart;
 		Term *goal;
 
@@ -54,13 +63,6 @@ evalquery(Term *database, Term *query)
 Retry:
 		goal = goals->goal;
 
-		if(goal == nil){
-			goals = goals->next;
-			continue;
-		}
-
-		print("Solving goal %S\n", prettyprint(goal));
-
 		/* Find a clause where the head unifies with the goal */
 		Binding *bindings = nil;
 		Term *clause = findclause(dbstart, goal, &bindings);
@@ -74,28 +76,23 @@ Retry:
 				choicestack = cp;
 			}
 			goals = goals->next;
-			/* Apply bindings to all goals on the top of the stack, down to the "bodystart" goal */
+
+			/* Apply bindings to all goals on the stack. */
 			Goal *g;
-			for(g = goals; g != nil && g->goal != nil; g = g->next)
-				applybinding(g->goal, bindings);
+			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){
-				Goal *bodystart = malloc(sizeof(Goal));
-				bodystart->goal = nil;
-				bodystart->next = goals;
-				goals = bodystart;
-
 				Term *subgoal = copyterm(clause->children->next, nil);
 				applybinding(subgoal, bindings);
 				goals = addgoals(goals, subgoal);
 			}
 		}else{
-			if(choicestack == nil){
-				print("Fail\n");
-				return;
-			}
-			print("Backtracking...\n");
+			if(choicestack == nil)
+				return 0;
 			Choicepoint *cp = choicestack;
 			choicestack = cp->next;
 			/* freegoals(goals) */
@@ -105,7 +102,9 @@ Retry:
 			goto Retry;
 		}
 	}
-	print("Success.\n");
+	goals = goals->next;
+	unify(query, goals->goal, resultbindings);
+	return 1;
 }
 
 Goal *