feat: Cut

src/prolog/ast/logic/Clause.kt

@@ -7,6 +7,7 @@ import prolog.ast.terms.Functor
 import prolog.ast.terms.Goal
 import prolog.ast.terms.Head
 import prolog.builtins.True
+import prolog.exceptions.AppliedCut
 import prolog.logic.unifyLazy
 
 /**
@@ -28,9 +29,20 @@ abstract class Clause(private val head: Head, private val body: Body) : Resolven
             headAnswer.map { newHeadSubs ->
                 // If the body can be proven, yield the (combined) substitutions
                 body.satisfy(subs + newHeadSubs).forEach { bodyAnswer ->
-                    bodyAnswer.map { newBodySubs ->
-                        yield(Result.success(newHeadSubs + newBodySubs))
-                    }
+                    bodyAnswer.fold(
+                        onSuccess = { newBodySubs ->
+                            yield(Result.success(newHeadSubs + newBodySubs))
+                        },
+                        onFailure = { error ->
+                            if (error is AppliedCut) {
+                                // Find single solution and return immediately
+                                yield(Result.failure(AppliedCut(newHeadSubs + error.subs)))
+                                return@sequence
+                            } else {
+                                yield(Result.failure(error))
+                            }
+                        }
+                    )
                 }
             }
         }