diff --git a/src/main/scala/com/github/kmizu/scomb/SCombinator.scala b/src/main/scala/com/github/kmizu/scomb/SCombinator.scala
index 651cd5e..294b776 100644
--- a/src/main/scala/com/github/kmizu/scomb/SCombinator.scala
+++ b/src/main/scala/com/github/kmizu/scomb/SCombinator.scala
@@ -10,10 +10,10 @@ abstract class SCombinator[R] {self =>
 
   protected var recent: Option[Failure] = None
 
-  protected var fatal: Option[Error] = None
-
   protected val locations: mutable.Map[Int, Location] = mutable.Map[Int, Location]()
 
+  private[this] val DefaultLabel: String = "fail"
+
   lazy val space: Parser[String] = (
     $(" ") | $("\t") | $("\b") | $("\f") | $("\r\n") | $("\r") | $("\n")
   )
@@ -53,13 +53,12 @@ abstract class SCombinator[R] {self =>
           repeat(next1) match {
             case Success(result, next2) =>
               Success(value::result, next2)
-            case r@Error(_, _) => r
             case r => throw new RuntimeException("cannot be " + r)
           }
-        case Failure(message, next) =>
+        case Failure(message, next, DefaultLabel) =>
           Success(Nil, index)
-        case f@Error(_, _) =>
-          f
+        case failure@Failure(message, next, label) =>
+          failure
       }
       repeat(index) match {
         case r@Success(_, _) => r
@@ -150,20 +149,6 @@ abstract class SCombinator[R] {self =>
       }
     }
 
-    /**
-      * Return the same parser except it replace the failure
-      * message with <code>message</code>
-      * @param message
-      * @return
-      */
-    def replace(message: String): Parser[T] = parserOf{ index =>
-      this(index) match {
-        case r@Success(_, _) => r
-        case Failure(_, index) => Failure(message, index)
-        case Error(_, index) => Error(message, index)
-      }
-    }
-
     /**
       * Returns a sequential Parser consists of <code>this</code> and <code>rhs</code>.
       */
@@ -173,15 +158,11 @@ abstract class SCombinator[R] {self =>
           right(next1) match {
             case Success(value2, next2) =>
               Success(new ~(value1, value2), next2)
-            case failure@Failure(_, _) =>
+            case failure@Failure(_, _, _) =>
               failure
-            case fatal@Error(_, _) =>
-              fatal
           }
-        case failure@Failure(message, next) =>
+        case failure@Failure(_, _, _) =>
           failure
-        case fatal@Error(_, _) =>
-          fatal
       }
     }
 
@@ -191,13 +172,13 @@ abstract class SCombinator[R] {self =>
     def ? : Parser[Option[T]] = parserOf{index =>
       this(index) match {
         case Success(v, i) => Success(Some(v), i)
-        case Failure(message, i) => Success(None, index)
-        case error@Error(_, _) => error
+        case Failure(message, i, DefaultLabel) => Success(None, index)
+        case failure@Failure(_, _, _) => failure
       }
     }
 
     /**
-      * Returns a alternation Parser.
+      * Returns an alternation Parser.
       * It first trys <code>this</code>.
       * It trys <code>rhs</code> iff <code>this</code> failed.
       * @param rhs the alternation
@@ -207,8 +188,21 @@ abstract class SCombinator[R] {self =>
     def |[U >: T](rhs: Parser[U]): Parser[U] = parserOf{index =>
       this(index) match {
         case success@Success(_, _) => success
-        case Failure(_, _) => rhs(index)
-        case fatal@Error(_, _) => fatal
+        case Failure(_, _, DefaultLabel) => rhs(index)
+        case failure@Failure(_, _, _) => failure
+      }
+    }
+
+    /**
+      * Returns an alternation parser.
+      * It first trys <code>this</code>.
+      * It trys <cdde>rhs></code> iff <code>this</code> failed and parameters are appropriate catchLabels.
+      */
+    def |~[U >: T](rhs: Parser[U], catchLabels: String*): Parser[U] = parserOf{index =>
+      this(index) match {
+        case success@Success(_, _) => success
+        case Failure(_, _, label) if catchLabels.contains(label) => rhs(index)
+        case failure@Failure(_, _, _) => failure
       }
     }
 
@@ -227,9 +221,7 @@ abstract class SCombinator[R] {self =>
           s
         case (_, s@Success(_, _)) =>
           s
-        case (f@Failure(_, _), _) =>
-          f
-        case (f@Error(_, _), _) =>
+        case (f@Failure(_, _, _), _) =>
           f
       }
     }
@@ -248,38 +240,20 @@ abstract class SCombinator[R] {self =>
             Success(value, next)
           else
             Failure(message, index)
-        case failure@Failure(_, _) =>
+        case failure@Failure(_, _, _) =>
           failure
-        case fatal@Error(_, _) =>
-          fatal
       }
     }
 
-    /**
-      * Replace the failure parser with the error parser.
-      * It is used to suppress backtracks.
-      * @param message the error message
-      */
-    def withErrorMessage(message: String): Parser[T] = parserOf{ index =>
+    def labeled(newLabel: String): Parser[T] = parserOf{index =>
       this(index) match {
-        case r@Success(_, _) => r
-        case Failure(_, index) => Error(message, index)
-        case r@Error(_, _) => r
+        case success@Success(_, _) => success
+        case Failure(message, index, oldLabel) =>
+          Failure(message, index, newLabel)
       }
     }
 
-    /**
-      * This method is same as `withErrorMessage()` except for
-      * no message being specified.
-      * @return
-      */
-    def commit: Parser[T] = parserOf{index =>
-      this(index) match {
-        case r@Success(_, _) => r
-        case Failure(message, index)  => Error(message, index)
-        case r@Error(_, _) => r
-      }
-    }
+    def l(newLabel: String): Parser[T] = labeled(newLabel)
 
     /**
       * It is same as <code>filter</code>
@@ -293,8 +267,7 @@ abstract class SCombinator[R] {self =>
     def map[U](function: T => U): Parser[U] = parserOf{index =>
       this(index) match {
         case Success(value, next) => Success(function(value), next)
-        case failure@Failure(_, _) => failure
-        case fatal@Error(_, _) => fatal
+        case failure@Failure(_, _, _) => failure
       }
     }
 
@@ -317,10 +290,8 @@ abstract class SCombinator[R] {self =>
       this(index) match {
         case Success(value, next) =>
           function.apply(value).apply(next)
-        case failure@Failure(_, _) =>
+        case failure@Failure(_, _, _) =>
           failure
-        case fatal@Error(_, _) =>
-          fatal
       }
     }
   }
@@ -358,11 +329,9 @@ abstract class SCombinator[R] {self =>
   }
 
   /**
-    * A data constructor in the case parser failed. It can be recovered by <code>|</code> operator
-    * @param message the error message
-    * @param index the next index
-    */
-  case class Failure(override val message: String, override val index: Int) extends ParseNonSuccess {
+   * A data constructor in the case parser failed with catch-labels. It can be recovered by <code>|~</code> operator
+   */
+  case class Failure(override val message: String, override val index: Int, label: String) extends ParseNonSuccess {
     self.recent match {
       case None => self.recent = Some(this)
       case Some(failure) if index >= failure.index => self.recent = Some(this)
@@ -370,14 +339,8 @@ abstract class SCombinator[R] {self =>
     }
     override def value: Option[Nothing] = None
   }
-
-  /**
-    * A data constructor in the case parser failed. It must not be recovered.
-    * @param message the error message
-    * @param index the next index
-    */
-  case class Error(override val message: String, override val index: Int) extends ParseNonSuccess {
-    override def value: Option[Nothing] = None
+  object Failure {
+    def apply(message: String, index: Int): Failure = Failure(message, index, DefaultLabel)
   }
 
   /**
@@ -441,8 +404,12 @@ abstract class SCombinator[R] {self =>
     calculateLocations()
     root(0) match {
       case s@Success(_, _) => s
-      case f@Failure(_, _) => recent.get
-      case f@Error(_,  _) => f
+      case f@Failure(_, _, label) =>
+        if(label == DefaultLabel) {
+          this.recent.get
+        } else {
+          f
+        }
     }
   }
 
@@ -454,10 +421,12 @@ abstract class SCombinator[R] {self =>
         } else {
           Result.Failure(locations(i), s"unconsumed input:`${current(i)}`")
         }
-      case Failure(message, index) =>
-        Result.Failure(locations(index), message)
-      case Error(message, index) =>
-        Result.Failure(locations(index), message)
+      case Failure(message, index, label) =>
+        if(label == DefaultLabel) {
+          Result.Failure(locations(index), message)
+        } else {
+          Result.Failure(locations(index), s"${message} in <${label}>")
+        }
     }
   }
 
@@ -485,7 +454,7 @@ abstract class SCombinator[R] {self =>
       val substring = current(index)
       literal.findPrefixOf(substring) match {
         case Some(prefix) => Success(prefix, index + prefix.length)
-        case None => Failure(s"expected:`${literal}`", index)
+        case None => Failure(s"expected:`${literal}` actual: `${current(index)(0)}`", index)
       }
     }
   }
@@ -508,7 +477,7 @@ abstract class SCombinator[R] {self =>
     } else if(current(index).startsWith(literal)) {
       Success(literal, index + literal.length)
     } else {
-      Failure(s"expected:`${literal}`", index)
+      Failure(s"expected:`${literal}` actual:`${current(index)(0)}`", index)
     }
   }
 
@@ -529,8 +498,7 @@ abstract class SCombinator[R] {self =>
   final def not(parser: Parser[Any]): Parser[Any] = parserOf{index =>
     parser(index) match {
       case Success(_, _) => Failure("not expected", index)
-      case Failure(_, _) => Success("", index)
-      case f@Error(_, _) => f
+      case Failure(_, _, _) => Success("", index)
     }
   }
 
diff --git a/src/test/scala/com/github/kmizu/scomb/JsonSpec.scala b/src/test/scala/com/github/kmizu/scomb/JsonSpec.scala
index a41366a..ce72660 100644
--- a/src/test/scala/com/github/kmizu/scomb/JsonSpec.scala
+++ b/src/test/scala/com/github/kmizu/scomb/JsonSpec.scala
@@ -44,25 +44,25 @@ class JsonSpec extends FunSpec with DiagrammedAssertions {
     lazy val jobject: P[JValue] = rule{for {
       _ <- LBRACE
       properties <- pair.repeat0By(COMMA)
-      _ <- RBRACE
+      _ <- RBRACE.l("RBRACE")
     } yield JObject(properties:_*)}
 
     lazy val pair: P[(String, JValue)] = rule{for {
       key <- string
-      _ <- COLON
+      _ <- COLON.l("COLON")
       value <- jvalue
     } yield (key, value)}
 
     lazy val jarray: P[JValue] = rule{for {
       _ <- LBRACKET
       elements <- jvalue.repeat0By(COMMA)
-      _ <- RBRACKET
+      _ <- RBRACKET.l("rbracket")
     } yield JArray(elements:_*)}
 
     lazy val string: Parser[String] = rule{for {
       _ <- $("\"")
       contents <- ($("\\") ~ any ^^ { case _ ~ ch => escape(ch).toString} | except('"')).*
-      _ <- $("\"")
+      _ <- $("\"").l("double quote")
       _ <- space.*
     } yield contents.mkString}
 
@@ -139,7 +139,15 @@ class JsonSpec extends FunSpec with DiagrammedAssertions {
     it("cannot parse incorrect object") {
       val failure = parse("{").asInstanceOf[Result.Failure]
       assert(Location(1, 2) == failure.location)
-      assert("""expected:`}` actual:EOF""" == failure.message)
+      assert("""expected:`}` actual:EOF in <RBRACE>""" == failure.message)
+    }
+  }
+
+  describe("The JsonParser") {
+    it("cannot parse incorrect array") {
+      val failure = parse("[1, 2, ]").asInstanceOf[Result.Failure]
+      assert(Location(1, 6) == failure.location)
+      assert("""expected:`]` actual:`,` in <rbracket>""" == failure.message)
     }
   }
 }
diff --git a/src/test/scala/com/github/kmizu/scomb/RegularExpressionSpec.scala b/src/test/scala/com/github/kmizu/scomb/RegularExpressionSpec.scala
index 259817a..3323885 100644
--- a/src/test/scala/com/github/kmizu/scomb/RegularExpressionSpec.scala
+++ b/src/test/scala/com/github/kmizu/scomb/RegularExpressionSpec.scala
@@ -70,7 +70,7 @@ class RegularExpressionSpec extends FunSpec with DiagrammedAssertions {
       input = "(1|9)*"
       assert(parse(input) == Result.Success(Repeat(Choice(Value('1'), Value('9')))))
       input = "*"
-      assert(parse(input) == Result.Failure(Location(1, 1), "expected:`\\`"))
+      assert(parse(input) == Result.Failure(Location(1, 1), "expected:`\\` actual:`*`"))
     }
   }
 }