function.scala

来自「JAVA 语言的函数式编程扩展」· SCALA 代码 · 共 148 行

/*                     __                                               *\
**     ________ ___   / /  ___     Scala API                            **
**    / __/ __// _ | / /  / _ |    (c) 2003-2007, LAMP/EPFL             **
**  __\ \/ /__/ __ |/ /__/ __ |                                         **
** /____/\___/_/ |_/____/_/ | |                                         **
**                          |/                                          **
\*                                                                      */

// $Id: Function.scala 14483 2008-04-02 14:43:16Z odersky $


package scala

/** A module defining utility methods for higher-order functional programming.
 *
 *  @author  Martin Odersky
 *  @version 1.0, 29/11/2006
 */
object Function {

  /** Given a sequence of functions <code>f<sub>1</sub></code>, ...,
   *  <code>f<sub>n</sub></code>, return the function <code>f<sub>1</sub>
   *  andThen ... andThen f<sub>n</sub></code>.
   *
   *  @param fs The given sequence of functions
   *  @return   ...
   */
  def chain[a](fs: Seq[a => a]): a => a = { x => (x /: fs) ((x, f) => f(x)) }

  /** The constant function */
  def const[T, U](x: T)(y: U): T = x

  /** Currying for functions of arity 2. This transforms a function
   *  of arity 2 into a a unary function returning another unary function.
   *
   *  @param f  ...
   *  @return   ...
   */
  def curried[a1, a2, b](f: (a1, a2) => b): a1 => a2 => b = {
    x1 => x2 => f(x1, x2)
  }

  /** Currying for functions of arity 3.
   *
   *  @param f  ...
   *  @return   ...
   */
  def curried[a1, a2, a3, b](f: (a1, a2, a3) => b): a1 => a2 => a3 => b = {
    x1 => x2 => x3 => f(x1, x2, x3)
  }

  /** Currying for functions of arity 4.
   */
  def curried[a1, a2, a3, a4, b](f: (a1, a2, a3, a4) => b): a1 => a2 => a3 => a4 => b = {
    x1 => x2 => x3 => x4 => f(x1, x2, x3, x4)
  }

  /** Currying for functions of arity 5.
   */
  def curried[a1, a2, a3, a4, a5, b](f: (a1, a2, a3, a4, a5) => b): a1 => a2 => a3 => a4 => a5 => b = {
    x1 => x2 => x3 => x4 => x5 => f(x1, x2, x3, x4, x5)
  }

  /** Uncurrying for functions of arity 2. This transforms a unary function
   *  returning another unary function into a function of arity 2.
   */
  def uncurried[a1, a2, b](f: a1 => a2 => b): (a1, a2) => b = {
    (x1, x2) => f(x1)(x2)
  }

  /** Uncurrying for functions of arity 3.
   */
  def uncurried[a1, a2, a3, b](f: a1 => a2 => a3 => b): (a1, a2, a3) => b = {
    (x1, x2, x3) => f(x1)(x2)(x3)
  }

  /** Uncurrying for functions of arity 4.
   */
  def uncurried[a1, a2, a3, a4, b](f: a1 => a2 => a3 => a4 => b): (a1, a2, a3, a4) => b = {
    (x1, x2, x3, x4) => f(x1)(x2)(x3)(x4)
  }

  /** Uncurrying for functions of arity 5.
   */
  def uncurried[a1, a2, a3, a4, a5, b](f: a1 => a2 => a3 => a4 => a5 => b): (a1, a2, a3, a4, a5) => b  =  {
    (x1, x2, x3, x4, x5) => f(x1)(x2)(x3)(x4)(x5)
  }

  /** Tupling for functions of arity 2. This transforms a function
   *  of arity 2 into a unary function that takes a pair of arguments.
   *
   *  @param f  ...
   *  @return   ...
   */
  def tupled[a1, a2, b](f: (a1, a2) => b): Tuple2[a1, a2] => b = {
    case Tuple2(x1, x2) => f(x1, x2)
  }

  /** Tupling for functions of arity 3. This transforms a function
   *  of arity 3 into a unary function that takes a triple of arguments.
   */
  def tupled[a1, a2, a3, b](f: (a1, a2, a3) => b): Tuple3[a1, a2, a3] => b = {
    case Tuple3(x1, x2, x3) => f(x1, x2, x3)
  }

  /** Tupling for functions of arity 4. This transforms a function
   *  of arity 4 into a unary function that takes a 4-tuple of arguments.
   */
  def tupled[a1, a2, a3, a4, b](f: (a1, a2, a3, a4) => b): Tuple4[a1, a2, a3, a4] => b = {
    case Tuple4(x1, x2, x3, x4) => f(x1, x2, x3, x4)
  }

  /** Tupling for functions of arity 5. This transforms a function
   *  of arity 5 into a unary function that takes a 5-tuple of arguments.
   */
  def tupled[a1, a2, a3, a4, a5, b](f: (a1, a2, a3, a4, a5) => b): Tuple5[a1, a2, a3, a4, a5] => b = {
    case Tuple5(x1, x2, x3, x4, x5) => f(x1, x2, x3, x4, x5)
  }

  /** Un-tupling for functions of arity 2. This transforms a function taking
   *  a pair of arguments into a binary function which takes each argument separately.
   */
  def untupled[a1, a2, b](f: Tuple2[a1, a2] => b): (a1, a2) => b = {
    (x1, x2) => f(Tuple2(x1, x2))
  }

  /** Un-tupling for functions of arity 3. This transforms a function taking
   *  a triple of arguments into a ternary function which takes each argument separately.
   */
  def untupled[a1, a2, a3, b](f: Tuple3[a1, a2, a3] => b): (a1, a2, a3) => b = {
    (x1, x2, x3) => f(Tuple3(x1, x2, x3))
  }

  /** Un-tupling for functions of arity 4. This transforms a function taking
   *  a 4-tuple of arguments into a function of arity 4 which takes each argument separately.
   */
  def untupled[a1, a2, a3, a4, b](f: Tuple4[a1, a2, a3, a4] => b): (a1, a2, a3, a4) => b = {
    (x1, x2, x3, x4) => f(Tuple4(x1, x2, x3, x4))
  }

  /** Un-tupling for functions of arity 5. This transforms a function taking
   *  a 5-tuple of arguments into a function of arity 5 which takes each argument separately.
   */
  def untupled[a1, a2, a3, a4, a5, b](f: Tuple5[a1, a2, a3, a4, a5] => b): (a1, a2, a3, a4, a5) => b = {
    (x1, x2, x3, x4, x5) => f(Tuple5(x1, x2, x3, x4, x5))
  }
}