3 ms·
> I wonder why auto-curried function syntax has become so ubiquitous in explaining this. I think it's primarily because this is the form you use them in in a l
by Twisol 5y ago
> I wonder why auto-curried function syntax has become so ubiquitous in explaining this.
I think it's primarily because this is the form you use them in in a language like Haskell. Most explanations are exported from Haskell in one way or another, so they're deeply colored by Haskellisms.
It's the same reason why `ap` and `bind` are generally preferred over `times` and `join` -- in Haskell you can even use `f <$> a <*> b`, which is a deeply clever use of infix `fmap` and `ap` that drives a syntactic analogy with regular function application, `f a b`. Try doing that in another language and you'll barf. And do-notation desugars most cleanly into >>=, so that's where Haskell-oriented explanations start from.
If you implement these in Java (which you can, you just can't abstract over T), it looks like this:
class List<A> {
<B> List<A> map(Function<A, B> f) { ... }
<B, C> List<C> map2(List<B> other, BiFunction<A, B, C> f) { ... }
<B> List<B> flatMap(Function<A, List<B>> f) { ... }
// bonus; note that these make more sense static
static <A, B> List<Pair<A, B>> times(List<A> as, List<B> bs) { ... }
// in fact, this one has to be static
static <A> List<A> join(List<List<A>> aas) { ... }
}
That is, the second argument `T a` in the top poster's comment becomes the implicit `this` parameter for instance methods. I find the `static` alternatives often make more syntactic sense in context; just goes to show that one language's norms don't always transfer.
- dunefox 5y agoThat version is extremely noisy, imo.
- marcosdumay 5y agoI once had to add logging to a large set of methods in C#, so I thought, well, let's make a function decorator like Python or Haskell, there's no reason it wouldn't work on C#. Well, it indeed worked perfectly well. But the amount of noise added to satisfy the type checker was larger than reimplementing the log procedure at each place.
- Twisol 5y agoThe version in Java? Yes, because it's Java.
- tel 5y agoYou can also look at the Scala implementations if you like. Scala has HKTs so you can write it all directly. trait Functor[F[_]] { def map[A, B](f: A => B)(x: F[A]): F[B] } trait Applicative[F[_]] extends Functor[F] { def pure[A](a: A): F[A] def apply[A, B](f: F[A => B])(x: F[A]): F[B] def product[A, B](xa: F[A], xb: F[B]): F[(A, B)] } trait Monad[F[_]] extends Applicative[F] { def bind[A, B](f: A => F[B])(x: F[A]): F[B] def join[A](x: F[F[A]]): F[A] }