Checkpoint

src/prolog/components/expressions/Clause.kt

@@ -0,0 +1,35 @@
+package prolog.components.expressions
+
+import prolog.components.Functor
+import prolog.components.Goal
+import prolog.components.terms.Head
+import prolog.components.terms.Term
+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.
+ *
+ * A clause consists of a [Head] and body separated by the [neck][prolog.terms.Neck] operator, or it is a [Fact].
+ *
+ * @see [prolog.components.terms.Variable]
+ * @see [Predicate]
+ */
+abstract class Clause(val head: Head, val body: Body = emptyList()) : Expression {
+    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 toString(): String {
+        return when {
+            body.isEmpty() -> head.toString()
+            else -> "$head :- ${body.joinToString(", ")}"
+        }
+    }
+}