Checkpoint

src/prolog/builtins/control.kt

@@ -1,15 +1,18 @@
 package prolog.builtins
 
+import prolog.Substitution
 import prolog.components.expressions.Operand
 import prolog.components.expressions.Operator
 import prolog.components.terms.Atom
 import prolog.components.terms.Body
+import prolog.components.terms.Term
+import prolog.components.terms.Variable
 
 /**
  * Always fail.
  */
 class Fail: Atom("fail"), Body {
-    override fun prove(): Boolean = false
+    override fun prove(): Sequence<Substitution> = emptySequence()
 }
 
 /**
@@ -21,7 +24,7 @@ typealias False = Fail
  * Always succeed.
  */
 class True: Atom("true"), Body {
-    override fun prove(): Boolean = true
+    override fun prove(): Sequence<Substitution> = sequenceOf(emptyMap())
 }
 
 // TODO Repeat/0
@@ -32,10 +35,16 @@ class True: Atom("true"), Body {
  * Conjunction (and). True if both Goal1 and Goal2 are true.
  */
 class Conjunction(leftOperand: Operand, rightOperand: Operand) : Operator(Atom(","), leftOperand, rightOperand) {
-    override fun prove(): Boolean {
-        val left = leftOperand?.prove() ?: true
-        val right = rightOperand.prove()
-        return left && right
+    override fun prove(): Sequence<Substitution> = sequence {
+        if (leftOperand != null) {
+            leftOperand.prove().forEach { left ->
+                rightOperand.prove().forEach { right ->
+                    yield(left + right)
+                }
+            }
+        } else {
+            yieldAll(rightOperand.prove())
+        }
     }
 }
 
@@ -43,9 +52,10 @@ class Conjunction(leftOperand: Operand, rightOperand: Operand) : Operator(Atom("
  * Disjunction (or). True if either Goal1 or Goal2 succeeds.
  */
 class Disjunction(leftOperand: Operand, rightOperand: Operand) : Operator(Atom(";"), leftOperand, rightOperand) {
-    override fun prove(): Boolean {
-        val left = leftOperand?.prove() ?: false
-        val right = rightOperand.prove()
-        return left || right
+    override fun prove(): Sequence<Substitution> = sequence {
+        if (leftOperand != null) {
+            yieldAll(leftOperand.prove())
+        }
+        yieldAll(rightOperand.prove())
     }
 }