@Override

public Class<? super Functor<?, F>> type() {

return Functor.class;

}

@Override

public void test(Equivalence<Functor<?, F>> equivalence) {

Present.<String>present((x, y) -> x + "\n\t - " + y)

.<Fn1<Equivalence<Functor<?, F>>, Maybe<String>>>foldMap(

fn -> fn.apply(equivalence),

asList(this::testIdentity,

this::testComposition))

.match(IO::io,

s -> throwing(new AssertionError("The following Functor laws did not hold for instance of " +

equivalence + ": \n\t - " + s)))

.unsafePerformIO();

}

private Maybe<String> testIdentity(Equivalence<Functor<?, F>> equivalence) {

return equivalence.invMap(f -> f.fmap(id())).equals(equivalence)

? nothing()

: just("identity (f.fmap(identity()).equals(f))");

}

private Maybe<String> testComposition(Equivalence<Functor<?, F>> equivalence) {

Fn1<Integer, Integer> g = x -> x * 3;

Fn1<Integer, Integer> h = x -> x - 2;

return equivalence.invMap(f -> f.fmap(constantly(1)).fmap(g).fmap(h))

.equals(equivalence.invMap(f -> f.fmap(constantly(1)).fmap(g.fmap(h))))

? nothing()

: just("composition (functor.fmap(f.contraMap(g)).equals(functor.fmap(g).fmap(f)))");

}