diff --git a/app/src/main/kotlin/io/smnp/evaluation/evaluator/ConditionEvaluator.kt b/app/src/main/kotlin/io/smnp/evaluation/evaluator/ConditionEvaluator.kt
index 7be70a8..1615d8d 100644
--- a/app/src/main/kotlin/io/smnp/evaluation/evaluator/ConditionEvaluator.kt
+++ b/app/src/main/kotlin/io/smnp/evaluation/evaluator/ConditionEvaluator.kt
@@ -27,6 +27,6 @@ class ConditionEvaluator : Evaluator() {
             return defaultEvaluator.evaluate(falseBranchNode, environment)
         }
 
-        return EvaluatorOutput.fail()
+        return EvaluatorOutput.ok()
     }
 }
\ No newline at end of file
diff --git a/app/src/main/kotlin/io/smnp/evaluation/evaluator/NotOperatorEvaluator.kt b/app/src/main/kotlin/io/smnp/evaluation/evaluator/NotOperatorEvaluator.kt
index 79ed8bc..e299745 100644
--- a/app/src/main/kotlin/io/smnp/evaluation/evaluator/NotOperatorEvaluator.kt
+++ b/app/src/main/kotlin/io/smnp/evaluation/evaluator/NotOperatorEvaluator.kt
@@ -3,17 +3,23 @@ package io.smnp.evaluation.evaluator
 import io.smnp.dsl.ast.model.node.Node
 import io.smnp.dsl.ast.model.node.NotOperatorNode
 import io.smnp.environment.Environment
+import io.smnp.error.EvaluationException
 import io.smnp.evaluation.model.entity.EvaluatorOutput
+import io.smnp.type.enumeration.DataType
 import io.smnp.type.model.Value
 
 class NotOperatorEvaluator : Evaluator() {
+    val evaluator = assert(ExpressionEvaluator(), "expression")
     override fun supportedNodes() = listOf(NotOperatorNode::class)
 
     override fun tryToEvaluate(node: Node, environment: Environment): EvaluatorOutput {
-        val evaluator = BoolLiteralEvaluator()
         val (_, operandNode) = (node as NotOperatorNode)
-        val operand = assert(evaluator, "bool").evaluate(operandNode, environment)
+        val operand = evaluator.evaluate(operandNode, environment).value!!
 
-        return EvaluatorOutput.value(Value.bool(!(operand.value!!.value as Boolean)))
+        if(operand.type != DataType.BOOL) {
+            throw EvaluationException("Only bool types can be negated", operandNode.position)
+        }
+
+        return EvaluatorOutput.value(Value.bool(!(operand.value as Boolean)))
     }
 }
\ No newline at end of file