What's the next step to learning Haskell after monads?

Question

I\'ve been gradually learning Haskell, and even feel like I\'ve got a hang of monads. However, there\'s still a lot of more exotic stuff that I barely understand, like Arrows, A

Answer 1

You know all you need to go forth and write code. But if you're looking for more Haskell-y things to learn about, may I suggest:

• Type families. Very handy feature. It basically gives you a way to write functions on the level of types, which is handy when you're trying to write a function whose parameters are polymorphic in a very precise way. One such example:

data TTrue = TTrue
data FFalse = FFalse


class TypeLevelIf tf a b where
  type If tf a b
  weirdIfStatement :: tf -> a -> b -> tf a b

instance TypeLevelIf TTrue a b where
  type If TTrue a b = a
  weirdIfStatement TTrue a b = a

instance TypeLevelIf FFalse a b where
  type If FFalse a b = b
  weirdIfStatement FFalse a b = a

This gives you a function that behaves like an if statement, but is able to return different types based on the truth value it is given.

If you're curious about type-level programming, type families provide one avenue into this topic.

• Template Haskell. This is a huge subject. It gives you a power similar to macros in C, but with much more type safety.

• Learn about some of the leading Haskell libraries. I can't count how many times parsec has enabled me to write an insanely useful utility quickly. dons periodically publishes a list of popular libraries on hackage; check it out.