Implement the NULL primitive

bjforth/src/main/java/bjforth/primitives/NULL.java

@@ -0,0 +1,28 @@
+/*
+ * Copyright 2024 Bahman Movaqar
+ *
+ * This file is part of bjForth.
+ *
+ * bjForth is free software: you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * bjForth is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+ * for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with bjForth. If not, see <https://www.gnu.org/licenses/>.
+ */
+package bjforth.primitives;
+
+import bjforth.machine.Machine;
+
+public class NULL implements Primitive {
+  @Override
+  public void execute(Machine machine) {
+    machine.pushToParameterStack((Object) null);
+  }
+}

bjforth/src/main/java/bjforth/primitives/PrimitiveFactory.java

@@ -171,6 +171,8 @@ static Primitive NUMBER() {
     return containerNUMBER.get();
   }
 
+  private static PrimitiveContainer containerNULL = new PrimitiveContainer(NULL::new);
+
   private static PrimitiveContainer containerOVER = new PrimitiveContainer(OVER::new);
 
   private static PrimitiveContainer containerPRINT = new PrimitiveContainer(PRINT::new);
@@ -308,6 +310,7 @@ static Primitive WORD() {
           containerNEQU,
           containerNROT,
           containerNUMBER,
+          containerNULL,
           containerOVER,
           containerPRINT,
           containerPRINTLN,

bjforth/src/test/java/bjforth/primitives/NULLTest.java

@@ -0,0 +1,49 @@
+/*
+ * Copyright 2024 Bahman Movaqar
+ *
+ * This file is part of bjForth.
+ *
+ * bjForth is free software: you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * bjForth is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+ * for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with bjForth. If not, see <https://www.gnu.org/licenses/>.
+ */
+package bjforth.primitives;
+
+import static bjforth.machine.BootstrapUtils.getPrimitiveAddress;
+import static bjforth.machine.MachineAssertions.assertThat;
+import static bjforth.machine.MachineBuilder.aMachine;
+import static bjforth.machine.MachineStateBuilder.aMachineState;
+import static bjforth.machine.ParameterStackBuilder.aParameterStack;
+import static org.junit.jupiter.api.Assertions.*;
+
+import org.junit.jupiter.api.Test;
+
+class NULLTest {
+
+  @Test
+  void workOk() {
+    // GIVEN
+    var NULLaddr = getPrimitiveAddress("NULL");
+    var actualState =
+        aMachineState()
+            .withInstrcutionPointer(NULLaddr)
+            .withParameterStack(aParameterStack().build())
+            .build();
+    var machine = aMachine().withState(actualState).build();
+
+    // WHEN
+    machine.step();
+
+    // THEN
+    assertThat(actualState).hasParameterStackEqualTo(aParameterStack().with((Object) null).build());
+  }
+}

docs/Primitives.md

@@ -67,6 +67,7 @@ In the following table, which lists all the primitives
 | `<>`        | `x y     - z`       | NEQU           |                                                  |
 | `-ROT`      | `a b c   - c b a`   | NROT           |                                                  |
 | `NUMBER`    | `        - x`       |                |                                                  |
+| `NULL`      | `        - null`    |                |                                                  |
 | `OVER`      | `a b     - a b a`   |                |                                                  |
 | `PRINT`     | `a       - a`       |                |                                                  |
 | `PRINTLN`   | `a       - a`       |                |                                                  |