diff --git a/evaluator/evaluator.go b/evaluator/evaluator.go
index c017e20..3bb5c1a 100644
--- a/evaluator/evaluator.go
+++ b/evaluator/evaluator.go
@@ -82,8 +82,6 @@ func evalPrefixAtom(operator string, right object.Object) object.Object {
 	switch operator {
 	case "-":
 		return evalMinusPrefix(right)
-	case "!":
-		return evalExclamationPrefix(right)
 	default:
 		return newError("unknown operator: %s%s", operator, right)
 	}
@@ -98,17 +96,6 @@ func evalMinusPrefix(right object.Object) object.Object {
 	return &object.Integer{Value: -value}
 }
 
-func evalExclamationPrefix(right object.Object) object.Object {
-	switch right {
-	case True:
-		return False
-	case False:
-		return True
-	default:
-		return newError("unknown operator: !%s", right)
-	}
-}
-
 func evalSymbol(symbol *ast.Symbol, env *object.Environment) object.Object {
 	builtintFunc, ok := builtins[symbol.Value]
 	if ok {
diff --git a/evaluator/evaluator_test.go b/evaluator/evaluator_test.go
index 77d23ad..cb180ea 100644
--- a/evaluator/evaluator_test.go
+++ b/evaluator/evaluator_test.go
@@ -138,16 +138,6 @@ func TestEvalBooleanExpression(t *testing.T) {
 			input:    "false",
 			expected: false,
 		},
-		{
-			name:     "negation of true",
-			input:    "!true",
-			expected: false,
-		},
-		{
-			name:     "negation of false",
-			input:    "!false",
-			expected: true,
-		},
 		{
 			name: "equation symbol: return true",
 			input: `
@@ -280,6 +270,28 @@ func TestEvalBooleanExpression(t *testing.T) {
 				}`,
 			expected: false,
 		},
+		{
+			name: "negation of true",
+			input: `
+				{
+					"command": {
+						"symbol": "!",
+						"args": true
+					}
+				}`,
+			expected: false,
+		},
+		{
+			name: "negation of false",
+			input: `
+				{
+					"command": {
+						"symbol": "!",
+						"args": false
+					}
+				}`,
+			expected: true,
+		},
 	}
 
 	for _, tt := range tests {