Fn2.java

package org.enumerable.lambda;

/**
 * A function that takes two arguments.
 */
@SuppressWarnings("serial")
public abstract class Fn2<A1, A2, R> extends Fn1<A1, R> {

    public abstract R call(A1 a1, A2 a2);

    public R call(A1 a1) {
        return call(a1, default$2());
    }

    protected A2 default$2() {
        return null;
    }

    @SuppressWarnings("unchecked")
    public R apply(Object... args) {
        if (args.length >= 2)
            return call((A1) args[0], (A2) args[1]);
        return super.apply(args);
    }

    /**
     * Partial application, returns a {@link Fn1} which calls this function with
     * a1 as the first argument.
     */
    public Fn1<A2, R> partial(final A1 a1) {
        return new Fn1<A2, R>() {
            public R call(A2 a2) {
                return Fn2.this.call(a1, a2);
            }
        };
    }

    /**
     * Currying, returns a {@link Fn1} which takes a1 as its argument and
     * returns another Fn1 which takes a2, which invokes this function with a1
     * and a2 when called.
     */
    public Fn1<A1, Fn1<A2, R>> curry2() {
        return new Fn1<A1, Fn1<A2, R>>() {
            public Fn1<A2, R> call(final A1 a1) {
                return new Fn1<A2, R>() {
                    public R call(A2 a2) {
                        return Fn2.this.call(a1, a2);
                    }
                };
            }
        };
    }

    public Fn2<A1, A2, Boolean> complement() {
        return new Fn2<A1, A2, Boolean>() {
            public Boolean call(A1 a1, A2 a2) {
                return isFalseOrNull(Fn2.this.call(a1, a2));
            }
        };
    }

    public int arity() {
        return 2;
    }
}