Single clause queries

src/prolog/components/Functor.kt

@@ -1,9 +0,0 @@
-package prolog.components
-
-import prolog.components.terms.Atom
-
-data class Functor(val name: Atom, val arity: Int) {
-    override fun toString(): String {
-        return "${name.name}/${arity}"
-    }
-}

src/prolog/components/Program.kt

@@ -4,6 +4,8 @@ import prolog.builtins.True
 import prolog.components.expressions.Clause
 import prolog.components.expressions.Fact
 import prolog.components.expressions.Predicate
+import prolog.components.terms.Functor
+import prolog.components.terms.Goal
 
 /**
  * Prolog Program or database.

src/prolog/components/expressions/Clause.kt

@@ -1,7 +1,7 @@
 package prolog.components.expressions
 
-import prolog.components.Functor
+import prolog.components.terms.Functor
-import prolog.components.Goal
+import prolog.components.terms.Goal
 import prolog.components.terms.Head
 import prolog.components.terms.Term
 import prolog.unify

src/prolog/components/expressions/Expression.kt

@@ -1,6 +1,6 @@
 package prolog.components.expressions
 
-import prolog.components.Goal
+import prolog.components.terms.Goal
 
 interface Expression {
     fun evaluate(goal: Goal): Boolean

src/prolog/components/expressions/Predicate.kt

@@ -1,7 +1,7 @@
 package prolog.components.expressions
 
-import prolog.components.Functor
+import prolog.components.terms.Functor
-import prolog.components.Goal
+import prolog.components.terms.Goal
 
 /**
  * Collection of [Clause]s with the same [Functor].

src/prolog/components/terms/Atom.kt

@@ -1,10 +1,7 @@
 package prolog.components.terms
 
-import prolog.components.Functor
+open class Atom(val name: String): Goal() {
-import prolog.components.Goal
+    override val functor: Functor = "$name/_"
-
-open class Atom(val name: String): Head(), Term, Goal {
-    override val functor: Functor = Functor(this, 0)
 
     override fun toString(): String {
         return name

src/prolog/components/terms/Goal.kt

@@ -1,6 +1,6 @@
-package prolog.components
+package prolog.components.terms
 
-import prolog.components.terms.Term
+import prolog.components.Program
 
 /**
  * Question stated to the Prolog engine.
@@ -9,9 +9,7 @@ import prolog.components.terms.Term
  * A goal either [succeeds][prolog.builtins.True], in which case the variables in the compound terms have a binding,
  * or it fails if Prolog fails to prove it.
  */
-interface Goal: Term {
+abstract class Goal : Head() {
-    val functor: Functor
-
     fun prove(): Boolean {
         return Program.query(this)
     }

src/prolog/components/terms/Head.kt

@@ -1,7 +1,5 @@
 package prolog.components.terms
 
-import prolog.components.Functor
-
 /**
  * Part of a [Clause][prolog.components.expressions.Clause] before the [neck][prolog.terms.Neck] operator.
  *
@@ -11,3 +9,5 @@ import prolog.components.Functor
 abstract class Head: Term {
     abstract val functor: Functor
 }
+
+typealias Functor = String

src/prolog/components/terms/Structure.kt

@@ -1,10 +1,7 @@
 package prolog.components.terms
 
-import prolog.components.Functor
+open class Structure(val name: Atom, val arguments: List<Argument>): Goal() {
-import prolog.components.Goal
+    override val functor: Functor = "${name.name}/${arguments.size}"
-
-open class Structure(val name: Atom, val arguments: List<Argument>): Head(), Term, Goal {
-    override val functor: Functor = Functor(name, arguments.size)
 
     override fun toString(): String {
         return when {

src/prolog/unify.kt

@@ -3,7 +3,6 @@ package prolog
 import prolog.builtins.atomic
 import prolog.builtins.compound
 import prolog.builtins.variable
-import prolog.components.Goal
 import prolog.components.terms.Term
 import prolog.components.terms.Variable
 import prolog.components.terms.Structure