diff --git a/src/main/kotlin/io/smnp/evaluation/evaluator/DefaultEvaluator.kt b/src/main/kotlin/io/smnp/evaluation/evaluator/DefaultEvaluator.kt
index fce88f1..c908bc2 100644
--- a/src/main/kotlin/io/smnp/evaluation/evaluator/DefaultEvaluator.kt
+++ b/src/main/kotlin/io/smnp/evaluation/evaluator/DefaultEvaluator.kt
@@ -17,7 +17,8 @@ class DefaultEvaluator : Evaluator {
             forward(ListEvaluator(), ListNode::class),
             forward(MapEvaluator(), MapNode::class),
 
-            forward(MinusOperatorEvaluator(), MinusOperatorNode::class)
+            forward(MinusOperatorEvaluator(), MinusOperatorNode::class),
+            forward(NotOperatorEvaluator(), NotOperatorNode::class)
         ).evaluate(node, environment)
     }
 }
\ No newline at end of file
diff --git a/src/main/kotlin/io/smnp/evaluation/evaluator/Evaluator.kt b/src/main/kotlin/io/smnp/evaluation/evaluator/Evaluator.kt
index 31d52db..72225eb 100644
--- a/src/main/kotlin/io/smnp/evaluation/evaluator/Evaluator.kt
+++ b/src/main/kotlin/io/smnp/evaluation/evaluator/Evaluator.kt
@@ -1,6 +1,7 @@
 package io.smnp.evaluation.evaluator
 
 import io.smnp.dsl.ast.model.node.Node
+import io.smnp.error.EvaluationException
 import io.smnp.evaluation.environment.Environment
 import io.smnp.evaluation.model.entity.EvaluatorOutput
 import io.smnp.evaluation.model.enumeration.EvaluationResult
@@ -36,5 +37,19 @@ interface Evaluator {
                 }
             }
         }
+
+        fun assert(evaluator: Evaluator, expected: String): Evaluator {
+            return object : Evaluator {
+                override fun evaluate(node: Node, environment: Environment): EvaluatorOutput {
+                    val output = evaluator.evaluate(node, environment)
+
+                    if(output.result == EvaluationResult.FAILED) {
+                        throw EvaluationException("Expected $expected", node.position)
+                    }
+
+                    return output
+                }
+            }
+        }
     }
 }
\ No newline at end of file
diff --git a/src/main/kotlin/io/smnp/evaluation/evaluator/NotOperatorEvaluator.kt b/src/main/kotlin/io/smnp/evaluation/evaluator/NotOperatorEvaluator.kt
new file mode 100644
index 0000000..c5beb15
--- /dev/null
+++ b/src/main/kotlin/io/smnp/evaluation/evaluator/NotOperatorEvaluator.kt
@@ -0,0 +1,18 @@
+package io.smnp.evaluation.evaluator
+
+import io.smnp.data.model.Value
+import io.smnp.dsl.ast.model.node.Node
+import io.smnp.dsl.ast.model.node.NotOperatorNode
+import io.smnp.evaluation.environment.Environment
+import io.smnp.evaluation.evaluator.Evaluator.Companion.assert
+import io.smnp.evaluation.model.entity.EvaluatorOutput
+
+class NotOperatorEvaluator : Evaluator {
+    override fun evaluate(node: Node, environment: Environment): EvaluatorOutput {
+        val evaluator = BoolLiteralEvaluator()
+        val (_, operandNode) = (node as NotOperatorNode)
+        val operand = assert(evaluator, "bool").evaluate(operandNode, environment)
+
+        return EvaluatorOutput.value(Value.bool(!(operand.value!!.value as Boolean)))
+    }
+}
\ No newline at end of file