Checkpoint

src/prolog/components/expressions/Clause.kt

@@ -1,15 +1,9 @@
 package prolog.components.expressions
 
-import prolog.components.terms.Functor
-import prolog.components.terms.Goal
-import prolog.components.terms.Head
-import prolog.components.terms.Term
+import prolog.components.Resolvent
+import prolog.components.terms.*
 import prolog.unify
 
-// TODO Change this to the right type, supporting operators and normal Clauses
-//  Probably needs a new interface or abstract class (?)
-typealias Body = List<Term>
-
 /**
  * ‘Sentence’ of a Prolog program.
  *
@@ -18,18 +12,29 @@ typealias Body = List<Term>
  * @see [prolog.components.terms.Variable]
  * @see [Predicate]
  */
-abstract class Clause(val head: Head, val body: Body = emptyList()) : Expression {
+abstract class Clause(private val head: Head, private val body: Body? = null) : Resolvent {
     val functor: Functor = head.functor
-    override fun evaluate(goal: Goal): Boolean {
-        val result = unify(goal, head)
-        // TODO Evaluate the body
-        return result.isEmpty
+
+    override fun solve(goal: Goal): Boolean {
+        val unification = unify(goal, head)
+
+        if (unification.isEmpty) {
+            return false
+        }
+
+        val substitutions = unification.get()
+
+        val proven = body == null || body.prove()
+
+        substitutions.forEach { (variable, _) -> variable.unbind() }
+
+        return proven
     }
 
     override fun toString(): String {
         return when {
-            body.isEmpty() -> head.toString()
-            else -> "$head :- ${body.joinToString(", ")}"
+            body == null -> head.toString()
+            else -> "$head :- $body"
         }
     }
 }