UnaryFunctor.java :  » Development » jga-Generic-Algorithms » net » sf » jga » fn » Java Open Source

// ============================================================================
// $Id: UnaryFunctor.java,v 1.16 2006/11/30 05:03:42 davidahall Exp $
// Copyright (c) 2002-2005  David A. Hall
// ============================================================================
// The contents of this file are subject to the Common Development and
// Distribution License (CDDL), Version 1.0 (the License); you may not use this 
// file except in compliance with the License.  You should have received a copy
// of the the License along with this file: if not, a copy of the License is 
// available from Sun Microsystems, Inc.
//
// http://www.sun.com/cddl/cddl.html
//
// From time to time, the license steward (initially Sun Microsystems, Inc.) may
// publish revised and/or new versions of the License.  You may not use,  
// distribute, or otherwise make this file available under subsequent versions 
// of the License.
// 
// Alternatively, the contents of this file may be used under the terms of the 
// GNU Lesser General Public License Version 2.1 or later (the "LGPL"), in which
// case the provisions of the LGPL are applicable instead of those above. If you 
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package net.sf.jga.fn;

import java.io.Serializable;
import net.sf.jga.fn.adaptor.Bind;
import net.sf.jga.fn.adaptor.ChainBinary;
import net.sf.jga.fn.adaptor.ChainUnary;
import net.sf.jga.fn.adaptor.Generate;
import net.sf.jga.fn.adaptor.Identity;

/**
 * A Function Object that takes one argument and returns a result.  The
 * argument is of type <code>T</code>, and the result is of type <code>R</code>.
 * <p>
 * Copyright &copy; 2002-2005  David A. Hall
 *
 * @author <a href="mailto:davidahall@users.sourceforge.net">David A. Hall</a>
 **/

abstract public class UnaryFunctor<T, R> extends Functor<R> implements Serializable, Visitable {
    /**
     * Executes the function and returns the result.
     */
    abstract public R fn(T arg);

    /**
     * FactoryMethod that creates a UnaryFunctor that passes its argument to
     * the given functor, and uses the result as the argument to this
     * function. Given argument <b>x</b>, the new functor will return
     * <code>fn<sub>this</sub>(f(x)))</code>
     */
    public <F> UnaryFunctor<F,R> compose(UnaryFunctor<F,T> f) {
        return new ChainUnary<F,T,R>(this,f);
    }

    /**
     * FactoryMethod that creates a BinaryFunctor that passes its arguments to
     * the given functor, and uses the result as the argument to this
     * function. Given arguments <b>x</b> and <b>y</b>, the new functor will
     * return <code>fn<sub>this</sub>(f(x,y)))</code>
     */
    public <F1,F2> BinaryFunctor<F1,F2,R> compose(BinaryFunctor<F1,F2,T> f) {
        return new ChainBinary<F1,F2,T,R>(this, f);
    }

    /**
     * FactoryMethod that creates a Generator to create the argument to this
     * function.  The new functor will return
     * <code>fn<sub>this</sub>(gen())</code>.
     */

    public Generator<R> generate(Generator<T> gen) {
        return new Generate<T,R>(this, gen);
    }
    
    /**
     * FactoryMethod that binds the argument arguments to this function to a specific
     * value.  The new functor will return
     * <code>fn<sub>this</sub>(val)</code>.
     */

    public Generator<R> bind(T val) {
        return new Bind<T,R>(val, this);
    }
    
    // -----------------
    // Functor interface
    // -----------------
    
    /**
     * Executes the function and returns the result.
     */
    public R eval(Object... args) {
        // @SuppressWarnings
        // This generates an unchecked cast warning: we're crossing the line from
        // unsafe rawform code to typesafe generic code.  This interface is known
        // to be unsafe, and documented to the user as such.        
        return fn((T) args[0]);
    }

    // -------------------
    // Visitable interface
    // -------------------
    
    /**
     * No-op implementation of Visitable interface.
     */
    public void accept(Visitor v) {}
}