Nice/stdlib/nice/functional higher-order.nice,NONE,1.1

Update of /cvsroot/nice/Nice/stdlib/nice/functional
In directory sc8-pr-cvs1.sourceforge.net:/tmp/cvs-serv28672/stdlib/nice/functional

Added Files:
	higher-order.nice 
Log Message:
Some useful odds and ends

--- NEW FILE: higher-order.nice ---
/****************************************************************************
 *                                 N I C E                                  *
 *              A high-level object-oriented research language              *
 *                         (c) Daniel Bonniot 2003                          *
 *                                                                          *
 *  This package is free software; you can redistribute it and/or modify    *
 *  it under the terms of the GNU General Public License as published by    *
 *  Free Software Foundation; either version 2 of the License, or (at your  *
 *  option) any later version.                                              *
 *                                                                          *
 *  As a special exception, the copyright holders of this library give you  *
 *  permission to link this library with independent modules to produce an  *
 *  executable, regardless of the license terms of these independent        *
 *  modules, and to copy and distribute the resulting executable under      *
 *  terms of your choice.                                                   *
 ****************************************************************************/

/**
 * Higher-order functions - that is, functions which take other
 * functions as arguments, or which return functions.
 *
 * @author Bryn Keller <[email protected]>
 */
package nice.functional;

/**
 * Returns a function which returns the opposite of what
 * the original function would return.
 */
<T> T->boolean not(T->boolean func) = T t => !func(t);

/** 
 * Returns a function which always returns the same result,
 * no matter what argument it's called with.
 */
<T,U> U->T always(T constant) = U u => constant;

/**
 * Does nothing, simply returns the object it's passed.
 */
<T> T id(T thing) = thing;




//Tests 

void _testNot() {
  let f = int i => i > 1;
  assert f(2) == true && not(f)(2) == false;
}

void _testAlways() {
  let f = always(2);
  assert f(1) == 2 && f(3) == 2;
}

void _testID() {
  let o = new Object();
  assert id(o) == o;
}



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