Sync

src/prolog/ast/terms/AnonymousVariable.kt

@@ -1,8 +1,9 @@
 package prolog.ast.terms
 
 import io.Logger
+import prolog.Substitutions
 
-class AnonymousVariable(id: Int) : Variable("_$id") {
+class AnonymousVariable(private val id: Int) : Variable("_$id") {
     companion object {
         private var counter = 0
         fun create(): AnonymousVariable {
@@ -14,4 +15,7 @@ class AnonymousVariable(id: Int) : Variable("_$id") {
     }
 
     override fun toString(): String = "_"
+
+    override fun clone(): AnonymousVariable = AnonymousVariable(id)
+    override fun applySubstitution(subs: Substitutions): AnonymousVariable = this
 }

src/prolog/ast/terms/Atom.kt

@@ -21,4 +21,7 @@ open class Atom(val name: String) : Goal(), Head, Body, Resolvent {
     override fun hashCode(): Int {
         return javaClass.hashCode()
     }
+
+    override fun clone(): Atom = Atom(name)
+    override fun applySubstitution(subs: Substitutions): Atom = Atom(name)
 }

src/prolog/ast/terms/Body.kt

@@ -2,4 +2,4 @@ package prolog.ast.terms
 
 import prolog.ast.logic.Satisfiable
 
-interface Body : Satisfiable
+interface Body : Term, Satisfiable

src/prolog/ast/terms/Structure.kt

@@ -3,6 +3,7 @@ package prolog.ast.terms
 import prolog.Answers
 import prolog.Substitutions
 import prolog.ast.logic.Resolvent
+import prolog.logic.applySubstitution
 import prolog.logic.unifyLazy
 
 typealias Argument = Term
@@ -33,4 +34,10 @@ open class Structure(val name: Atom, var arguments: List<Argument>) : Goal(), He
     override fun hashCode(): Int {
         return javaClass.hashCode()
     }
+
+    override fun clone(): Structure = Structure(name, arguments)
+    override fun applySubstitution(subs: Substitutions): Structure = Structure(
+        name,
+        arguments.map { applySubstitution(it, subs) }
+    )
 }

src/prolog/ast/terms/Term.kt

@@ -1,14 +1,19 @@
 package prolog.ast.terms
 
+import prolog.Substitutions
 import prolog.logic.compare
+import prolog.ast.arithmetic.Integer
+import prolog.ast.arithmetic.Float
 
 /**
  * Value in Prolog.
  *
- * A [Term] is either a [Variable], [Atom], [Integer][prolog.ast.arithmetic.Integer],
- * [Float][prolog.ast.arithmetic.Float] or [CompoundTerm].
+ * A [Term] is either a [Variable], [Atom], [Integer],
+ * [Float] or [CompoundTerm].
  * In addition, SWI-Prolog also defines the type TODO string.
  */
-interface Term : Comparable<Term> {
+interface Term : Comparable<Term>, Cloneable {
     override fun compareTo(other: Term): Int = compare(this, other, emptyMap())
+    fun applySubstitution(subs: Substitutions): Term
+    public override fun clone(): Term
 }

src/prolog/ast/terms/Variable.kt

@@ -39,4 +39,7 @@ open class Variable(val name: String) : Term, Body, Expression, LogicOperand() {
     }
 
     override fun toString(): String = name
+
+    override fun clone(): Variable = Variable(name)
+    override fun applySubstitution(subs: Substitutions): Variable = this
 }