identity_monad.java

package com.ryangantt.monad;

/**
 * Implementation of the identity monad
 */
public class Identity<T> {
    public T value;
    
    public T getValue() {
        return value;
    }
    
    public void setValue(final T value) {
        this.value = value;
    }
    
    public String toString() {
        return String.valueOf(value);
    }
    
    public Identity(final T value) {
        setValue(value);
    }
    
    /**
     * Factories
     */
    
    private static interface Func<K, U> {
        public U apply(final K value);
    }
    
    public static <T, U> Identity<U> bind(final Identity<T> id, final Func<T, Identity<U>> k) {
        return k.apply(id.getValue());
    }
    
    public static <T> Identity<T> unit(final T value) {
        return new Identity<T>(value);
    }
    
    /**
     * Test
     */
    
    public static void main(final String[] args) {
        final Identity<Integer> result = Identity.bind(unit(5), new Func<Integer, Identity<Integer>>() {
            @Override
            public Identity<Integer> apply(final Integer x) {
                return bind(unit(6), new Func<Integer, Identity<Integer>>() {
                    @Override
                    public Identity<Integer> apply(final Integer y) {
                        return unit(x + y);
                    }
                });
            }
        });
        System.out.println("Result: " + result);
    }
}