prefix expressions

compiler/compiler.go

@@ -91,6 +91,21 @@ func (c *Compiler) Compile(node ast.Node) error {
 			c.emit(code.OpFalse)
 		}
 
+	case *ast.PrefixExpression:
+		err := c.Compile(node.Right)
+		if err != nil {
+			return err
+		}
+
+		switch node.Operator {
+		case "!":
+			c.emit(code.OpBang)
+		case "-":
+			c.emit(code.OpMinus)
+		default:
+			return fmt.Errorf("unknown operator %s", node.Operator)
+		}
+
 	}
 
 	return nil

compiler/compiler_test.go

@@ -68,6 +68,15 @@ func TestIntegerArithmetic(t *testing.T) {
 				code.Make(code.OpPop),
 			},
 		},
+		{
+			input:             "-1",
+			expectedConstants: []interface{}{1},
+			expectedInstructions: []code.Instructions{
+				code.Make(code.OpConstant, 0),
+				code.Make(code.OpMinus),
+				code.Make(code.OpPop),
+			},
+		},
 	}
 
 	runCompilerTests(t, tests)
@@ -151,6 +160,15 @@ func TestBooleanExpressions(t *testing.T) {
 				code.Make(code.OpPop),
 			},
 		},
+		{
+			input:             "!true",
+			expectedConstants: []interface{}{},
+			expectedInstructions: []code.Instructions{
+				code.Make(code.OpTrue),
+				code.Make(code.OpBang),
+				code.Make(code.OpPop),
+			},
+		},
 	}
 
 	runCompilerTests(t, tests)