Lift Framework example source code file (MonadicConversions.scala)

This example Lift Framework source code file (MonadicConversions.scala) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Lift Framework tags/keywords

boolean, false, false, list, monadiccondition, monadiccondition, monadicconversions, string, string, true, true

The Lift Framework MonadicConversions.scala source code

/*
 * Copyright 2008-2011 WorldWide Conferencing, LLC
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package net.liftweb 
package util 

/**
 * Holds the implicit conversions from/to MonadicCondition
 */
object MonadicConversions {

  implicit def bool2Monadic(cond: Boolean) = cond match {
    case true => True
    case _ => False(Nil)
  }

  implicit def monadic2Bool(cond: MonadicCondition): Boolean = cond match {
    case True => true
    case _ => false
  }

}

/**
 * A MonadicCondition allows building boolean expressions of the form
 * (a(0) && a(1) && .. && a(n)), where a(k) is a boolean expression, and
 * collecting the computation failures to a list of messages.
 *
 * <pre>
 * Example:
 *
 *   val isTooYoung = true;
 *   val isTooBad = false;
 *   val isTooStupid = true;
 *
 *   val exp = (!isTooYoung ~ "too young") &&
 *             (!isTooBad ~ "too bad") &&
 *             (!isTooStupid ~ "too stupid")
 *
 *   println(exp match {
 *     case False(msgs) => msgs mkString("Test failed because it is '", "' and '", "'.")
 *     case _ => "success"
 *   })
 * </pre>
 */
trait MonadicCondition {
  def && (cond: MonadicCondition): MonadicCondition
  def ~ (msg: String): MonadicCondition
}

case object True extends MonadicCondition {
  def && (cond: MonadicCondition): MonadicCondition = cond match {
    case f @ False(m) => f
    case _ => this
  }
  def ~ (msg: String): MonadicCondition = this
}

case class False(msgs: List[String]) extends MonadicCondition {
  def && (cond: MonadicCondition): MonadicCondition = cond match {
    case False(m) => False(m ::: msgs)
    case _ => this
  }
  def ~ (msg: String): MonadicCondition = False(msg :: msgs)
}