fix: Fixes

examples/basics/summer.pl

@@ -3,9 +3,7 @@ summer(Start, End, Sum) :-
     Start \== End,
     Next is Start + 1,
     summer(Next, End, Rest),
-    writeln(rest(Rest)),
+    Sum is Start + Rest.
-    Sum is Start + Rest,
-    writeln(sum(Sum)).
 
 my_sum :-
     write('Enter start: '),
@@ -17,6 +15,8 @@ my_sum :-
     write(Sum), nl.
 
 main :-
-    summer(1, 5, Sum).
+    Start = 1, End = 9,
+    summer(Start, End, Sum),
+    write('The sum of '), write(Start), write(' to '), write(End), write(' is: '), write(Sum), nl.
 
 :- initialization(main).

examples/meta/calculator.pl

@@ -0,0 +1,15 @@
+accumulator :-
+    Sum = 0,
+    shift(Number),
+    NewSum is Sum + Number,
+    write("Result is: "), writeln(NewSum).
+
+main :-
+    reset(accumulator, Number, Cont),
+    between(1, 5, Number),
+    forall()
+    call(Cont),
+    writeln("End of calculation").
+
+:- initialization(main).
+

src/prolog/ast/arithmetic/Integer.kt

@@ -3,8 +3,9 @@ package prolog.ast.arithmetic
 import prolog.Answers
 import prolog.Substitutions
 import prolog.ast.logic.LogicOperand
+import prolog.ast.terms.Body
 
-data class Integer(override val value: Int) : Number, LogicOperand() {
+data class Integer(override val value: Int) : Number, Body, LogicOperand() {
     // Integers are already evaluated
     override fun simplify(subs: Substitutions): Simplification = Simplification(this, this)
 

src/prolog/ast/logic/Clause.kt

@@ -6,6 +6,7 @@ import prolog.ast.Database.Program
 import prolog.ast.terms.*
 import prolog.builtins.True
 import prolog.flags.AppliedCut
+import prolog.flags.AppliedShift
 import prolog.logic.applySubstitution
 import prolog.logic.numbervars
 import prolog.logic.occurs
@@ -27,18 +28,23 @@ abstract class Clause(var head: Head, var body: Body) : Term, Resolvent {
         // Only if the body can be proven, the substitutions should be returned.
         // Do this in a lazy way.
 
+        val simplifiedGoal = applySubstitution(goal, subs)
+
         // Since we are only interested in substitutions in the goal (as opposed to the head of this clause),
         //  we can use variable renaming and filter out the substitutions that are not in the goal.
         val (headEnd, headRenaming) = numbervars(head, Program.variableRenamingStart, emptyMap())
-        Program.variableRenamingStart = headEnd
+        val (goalEnd, goalRenaming) = numbervars(simplifiedGoal, headEnd, emptyMap())
+        Program.variableRenamingStart = goalEnd
+
+        val reverseGoalRenaming = goalRenaming.entries.associate { (key, value) -> value to key }
 
         val renamedHead = applySubstitution(head, headRenaming)
-        val simplifiedGoal = applySubstitution(goal, subs)
+        val renamedGoal = applySubstitution(simplifiedGoal, goalRenaming)
-        unifyLazy(simplifiedGoal, renamedHead, emptyMap()).forEach { headAnswer ->
+        unifyLazy(renamedGoal, renamedHead, emptyMap()).forEach { headAnswer ->
             headAnswer.map { headAndGoalSubs ->
                 // Filter the substitutions to only include those that map from head to goal
                 val headToGoalSubs = headAndGoalSubs.filterKeys { it in headRenaming.values }
-                val goalToHeadSubs = headAndGoalSubs.filterKeys { occurs(it as Variable, simplifiedGoal) }
+                val goalToHeadSubs = headAndGoalSubs.filterKeys { occurs(it as Variable, renamedGoal) }
                 val headResult = headToGoalSubs.filterKeys { key ->
                     goalToHeadSubs.any { occurs(key as Variable, it.value) }
                 }
@@ -47,24 +53,34 @@ abstract class Clause(var head: Head, var body: Body) : Term, Resolvent {
                     bodyAnswer.fold(
                         onSuccess = { bodySubs ->
                             // If the body can be proven, yield the (combined) substitutions
-                            val goalResult = goalToHeadSubs.mapValues { applySubstitution(it.value, bodySubs) }
+                            val renamedGoalResult = goalToHeadSubs.mapValues { applySubstitution(it.value, bodySubs) }
-                            val bodyResult = bodySubs.filterKeys { occurs(it as Variable, simplifiedGoal) }
+                            val goalResult =
+                                renamedGoalResult.mapKeys { applySubstitution(it.key, reverseGoalRenaming) }
+                            val renamedBodyResult = bodySubs.filterKeys { occurs(it as Variable, renamedGoal) }
+                            val bodyResult = renamedBodyResult.mapKeys { applySubstitution(it.key, reverseGoalRenaming) }
                             yield(Result.success(goalResult + headResult + bodyResult))
                         },
                         onFailure = { error ->
-                            if (error is AppliedCut) {
+                            when (error) {
-                                // Find single solution and return immediately
+                                is AppliedCut -> {
-                                if (error.subs != null) {
+                                    // Find single solution and return immediately
-                                    val bodySubs = error.subs
+                                    if (error.subs != null) {
-                                    val goalResult = goalToHeadSubs.mapValues { applySubstitution(it.value, bodySubs) }
+                                        val bodySubs = error.subs
-                                    val bodyResult = bodySubs.filterKeys { occurs(it as Variable, simplifiedGoal) }
+                                        val goalResult =
-                                    yield(Result.failure(AppliedCut(goalResult + headResult + bodyResult)))
+                                            goalToHeadSubs.mapValues { applySubstitution(it.value, bodySubs) }
-                                } else {
+                                        val bodyResult = bodySubs.filterKeys { occurs(it as Variable, renamedGoal) }
-                                    yield(Result.failure(AppliedCut()))
+                                        yield(Result.failure(AppliedCut(goalResult + headResult + bodyResult)))
+                                    } else {
+                                        yield(Result.failure(AppliedCut()))
+                                    }
+                                    return@sequence
                                 }
-                                return@sequence
+
-                            } else {
+                                is AppliedShift -> {
-                                yield(Result.failure(error))
+                                    yield(Result.failure(error))
+                                }
+
+                                else -> yield(Result.failure(error))
                             }
                         }
                     )

src/prolog/ast/terms/Body.kt

@@ -1,5 +1,8 @@
 package prolog.ast.terms
 
+import prolog.Substitutions
 import prolog.ast.logic.Satisfiable
 
-interface Body : Term, Satisfiable
+interface Body : Term, Satisfiable {
+    override fun applySubstitution(subs: Substitutions): Body
+}

src/prolog/builtins/controlOperators.kt

@@ -55,7 +55,7 @@ open class Conjunction(val left: LogicOperand, private val right: LogicOperand)
                 right.fold(
                     // If the right part succeeds, yield the result with the left substitutions
                     onSuccess = { rightSubs ->
-                        yield(Result.success(leftSubs + rightSubs))
+                        yield(Result.success(rightSubs + leftSubs))
                     },
                     onFailure = { exception ->
                         // If the right part fails, check if it's a cut
@@ -74,8 +74,8 @@ open class Conjunction(val left: LogicOperand, private val right: LogicOperand)
         }
 
         fun findNextCutSolution(appliedCut: AppliedCut): Answers = sequence {
-            val leftSubs = appliedCut.subs
+            val leftSubs = appliedCut.subs ?: emptyMap()
-            right.satisfy(subs + (appliedCut.subs!!)).firstOrNull()?.map { rightSubs ->
+            right.satisfy(subs + leftSubs).firstOrNull()?.map { rightSubs ->
                 // If the right part succeeds, yield the result with the left substitutions
                 yield(Result.success(leftSubs + rightSubs))
                 return@sequence

src/prolog/builtins/delimitedContinuationsOperators.kt

@@ -39,7 +39,7 @@ class Reset(private val goal: Goal, private val ball: Term, private val cont: Te
                     if (failure is AppliedShift) {
                         require(failure.cont != null) { "Shift must have a continuation" }
                         // Reset/3 succeeds immediately, binding Term1 to Term2 and Cont to the remainder of Goal.
-                        val shiftSubs = failure.subs
+                        val shiftSubs = failure.subs + subs
                         val appliedBall = applySubstitution(failure.ball, shiftSubs)
                         val appliedCont = applySubstitution(failure.cont, shiftSubs)
                         Conjunction(Unify(ball, appliedBall), Unify(appliedCont, cont))

tests/e2e/Examples.kt

@@ -27,7 +27,7 @@ class Examples {
 
     @Test
     fun debugHelper() {
-        loader.load("examples/meta/continuations.pl")
+        loader.load("examples/meta/mib_voorbeelden.pl")
     }
 
     @ParameterizedTest
@@ -60,6 +60,7 @@ class Examples {
         Arguments.of("forall.pl", "Only alice likes pizza.\n"),
         Arguments.of("fraternity.pl", "Citizen robespierre is eligible for the event.\nCitizen danton is eligible for the event.\nCitizen camus is eligible for the event.\n"),
         Arguments.of("liberty.pl", "Give me Liberty, or give me Death!\nI disapprove of what you say, but I will defend to the death your right to say it.\nThe revolution devours its own children.\nSo this is how liberty dies, with thunderous applause.\n"),
+        Arguments.of("summer.pl", "The sum of 1 to 9 is: 36\n"),
         Arguments.of("unification.pl", "While alice got an A, carol got an A, but bob did not get an A, dave did not get an A, unfortunately.\n"),
         Arguments.of("write.pl", "gpl zegt: dag(wereld)\n"),
     )