diff --git a/src/org/jetbrains/eval4j/interpreterLoop.kt b/src/org/jetbrains/eval4j/interpreterLoop.kt
index 06105bbf430..2fe8d3118ae 100644
--- a/src/org/jetbrains/eval4j/interpreterLoop.kt
+++ b/src/org/jetbrains/eval4j/interpreterLoop.kt
@@ -10,11 +10,21 @@ import org.objectweb.asm.tree.analysis.Interpreter
 import org.objectweb.asm.tree.JumpInsnNode
 import org.objectweb.asm.tree.VarInsnNode
 
-trait InterpreterResult
-object NOTHING_DONE: InterpreterResult
-class ExceptionThrown(val exception: Value): InterpreterResult
-class ValueReturned(val result: Value): InterpreterResult
-class AbnormalTermination(val message: String): InterpreterResult
+trait InterpreterResult {
+    fun toString(): String
+}
+
+class ExceptionThrown(val exception: Value): InterpreterResult {
+    override fun toString(): String = "Thrown $exception"
+}
+
+class ValueReturned(val result: Value): InterpreterResult {
+    override fun toString(): String = "Returned $result"
+}
+
+class AbnormalTermination(val message: String): InterpreterResult {
+    override fun toString(): String = "Terminated abnormally: $message"
+}
 
 trait InterpretationEventHandler {
 
@@ -42,7 +52,7 @@ fun interpreterLoop(
         handler: InterpretationEventHandler = InterpretationEventHandler.NONE
 ): InterpreterResult {
     val firstInsn = m.instructions.getFirst()
-    if (firstInsn == null) return NOTHING_DONE
+    if (firstInsn == null) throw IllegalArgumentException("Empty method")
 
     var currentInsn = firstInsn!!
 
diff --git a/src/org/jetbrains/eval4j/values.kt b/src/org/jetbrains/eval4j/values.kt
index 80ac78f9e81..c00a49fde68 100644
--- a/src/org/jetbrains/eval4j/values.kt
+++ b/src/org/jetbrains/eval4j/values.kt
@@ -7,36 +7,45 @@ trait Value : org.objectweb.asm.tree.analysis.Value {
     val asmType: Type
     val valid: Boolean
     override fun getSize(): Int = asmType.getSize()
+
+    override fun toString(): String
 }
 
 abstract class AbstractValue(
-        override val asmType: Type
+        override val asmType: Type,
+        private val asString: String
 ) : Value {
     override val valid = true
+
+    override fun toString() = asString
 }
 
 object NOT_A_VALUE: Value {
     override val asmType = Type.getType("<invalid>")
     override val valid = false
     override fun getSize(): Int = 1
+
+    override fun toString() = "NOT_A_VALUE"
 }
 
 object VOID_VALUE: Value {
     override val asmType: Type = Type.VOID_TYPE
     override val valid: Boolean = false
+    override fun toString() = "VOID_VALUE"
 }
 
 class NotInitialized(override val asmType: Type): Value {
     override val valid = false
+    override fun toString() = "NotInitialized: $asmType"
 }
 
-class IntValue(val value: Int, asmType: Type): AbstractValue(asmType)
-class LongValue(val value: Long): AbstractValue(Type.LONG_TYPE)
-class FloatValue(val value: Float): AbstractValue(Type.FLOAT_TYPE)
-class DoubleValue(val value: Double): AbstractValue(Type.DOUBLE_TYPE)
-class ObjectValue(val value: Any?, asmType: Type): AbstractValue(asmType)
+class IntValue(val value: Int, asmType: Type): AbstractValue(asmType, "$value")
+class LongValue(val value: Long): AbstractValue(Type.LONG_TYPE, "$value")
+class FloatValue(val value: Float): AbstractValue(Type.FLOAT_TYPE, "$value")
+class DoubleValue(val value: Double): AbstractValue(Type.DOUBLE_TYPE, "$value")
+class ObjectValue(val value: Any?, asmType: Type): AbstractValue(asmType, "$value")
 
-class LabelValue(val value: LabelNode): AbstractValue(Type.VOID_TYPE)
+class LabelValue(val value: LabelNode): AbstractValue(Type.VOID_TYPE, "label: ${value.getLabel()}")
 
 fun boolean(v: Boolean) = IntValue(if (v) 1 else 0, Type.BOOLEAN_TYPE)
 fun byte(v: Byte) = IntValue(v.toInt(), Type.BYTE_TYPE)