REPL checkpoint

src/prolog/Program.kt

@@ -1,5 +1,6 @@
 package prolog
 
+import Debug
 import prolog.ast.logic.Clause
 import prolog.ast.logic.Predicate
 import prolog.ast.logic.Resolvent
@@ -12,13 +13,16 @@ typealias Database = Program
  * Prolog Program or database.
  */
 object Program: Resolvent {
-    private var predicates: Map<Functor, Predicate> = emptyMap()
+    var predicates: Map<Functor, Predicate> = emptyMap()
 
     init {
         setup()
     }
 
     private fun setup() {
+        if (Debug.on) {
+            println("Setting up Prolog program...")
+        }
         // Initialize the program with built-in predicates
         load(listOf(
         ))

src/prolog/ast/logic/Clause.kt

@@ -18,7 +18,7 @@ import prolog.logic.unifyLazy
  * @see [prolog.ast.terms.Variable]
  * @see [Predicate]
  */
-abstract class Clause(private val head: Head, private val body: Body) : Resolvent {
+abstract class Clause(val head: Head, val body: Body) : Resolvent {
     val functor: Functor = head.functor
 
     override fun solve (goal: Goal, subs: Substitutions): Answers = sequence {

src/prolog/ast/logic/Predicate.kt

@@ -39,6 +39,11 @@ class Predicate : Resolvent {
      */
     fun add(clause: Clause) {
         require(clause.functor == functor) { "Clause functor does not match predicate functor" }
+
+        if (Debug.on) {
+            println("Adding clause $clause to predicate $functor")
+        }
+
         clauses.add(clause)
     }
 

src/prolog/ast/terms/Operator.kt

@@ -1,7 +1,5 @@
 package prolog.ast.terms
 
-import prolog.ast.arithmetic.Expression
-
 typealias Operand = Term
 
 abstract class Operator(

src/prolog/builtins/controlOperators.kt

@@ -39,7 +39,7 @@ class Cut() : Atom("!") {
 /**
  * Conjunction (and). True if both Goal1 and Goal2 are true.
  */
-class Conjunction(private val left: LogicOperand, private val right: LogicOperand) :
+class Conjunction(val left: LogicOperand, private val right: LogicOperand) :
     LogicOperator(Atom(","), left, right) {
     override fun satisfy(subs: Substitutions): Answers = sequence {
         // Satisfy the left part first, which either succeeds or fails