Add null literal

compiler/compiler.go

@@ -155,6 +155,9 @@ func (c *Compiler) Compile(node ast.Node) error {
 		integer := &object.Integer{Value: node.Value}
 		c.emit(code.OpConstant, c.addConstant(integer))
 
+	case *ast.Null:
+		c.emit(code.OpNull)
+
 	case *ast.Boolean:
 		if node.Value {
 			c.emit(code.OpTrue)

compiler/compiler_test.go

@@ -100,6 +100,14 @@ func TestBooleanExpressions(t *testing.T) {
 				code.Make(code.OpPop),
 			},
 		},
+		{
+			input:             "null",
+			expectedConstants: []interface{}{},
+			expectedInstructions: []code.Instructions{
+				code.Make(code.OpNull),
+				code.Make(code.OpPop),
+			},
+		},
 		{
 			input:             "1 > 2",
 			expectedConstants: []interface{}{1, 2},