ForAll

tests/prolog/builtins/OtherOperatorsTests.kt

@@ -0,0 +1,54 @@
+package prolog.builtins
+
+import org.junit.jupiter.api.Assertions.assertEquals
+import org.junit.jupiter.api.Assertions.assertTrue
+import org.junit.jupiter.api.Test
+import prolog.ast.Database.Program
+import prolog.ast.arithmetic.Integer
+import prolog.ast.logic.Rule
+import prolog.ast.terms.Atom
+import prolog.ast.terms.CompoundTerm
+import prolog.ast.terms.Variable
+import java.io.ByteArrayOutputStream
+import java.io.PrintStream
+
+class OtherOperatorsTests {
+    @Test
+    fun `forall(X is 1, X == 1)`() {
+        val forall = ForAll(Is(Variable("X"), Integer(1)), EvaluatesTo(Variable("X"), Integer(1)))
+
+        val result = forall.satisfy(emptyMap()).toList()
+
+        assertEquals(1, result.size)
+    }
+
+    /**
+     * @see [Forall instead of failure-driven loops](https://riptutorial.com/prolog/example/19554/forall-instead-of-failure-driven-loops#example)
+     */
+    @Test
+    fun `forall printer`() {
+        val printer = Rule(
+            CompoundTerm(Atom("print"), listOf(Variable("X"))),
+            ForAll(
+                Between(Integer(1), Variable("X"), Variable("Y")),
+                Write(Variable("Y"))
+            )
+        )
+        Program.load(listOf(printer))
+
+        // Set output
+        val outStream = ByteArrayOutputStream()
+        System.setOut(PrintStream(outStream))
+
+        var expected = ""
+        for (i in 1..5) {
+            val result = CompoundTerm(Atom("print"), listOf(Integer(i))).satisfy(emptyMap()).toList()
+            assertEquals(1, result.size)
+            assertTrue(result[0].isSuccess)
+
+            expected += "$i"
+            assertEquals(expected, outStream.toString())
+            outStream.reset()
+        }
+    }
+}