2018-08-21_tricky-haskell-questions.md

Tricky Haskell questions

These questions have insightful answers about some deep detail of Haskell.

let vs λ

Why do we have »let« syntax when we also have lambdas? What’s the difference between these two expressions?

(\x -> <expr>) y
let x = y in <expr>

newtype vs strict data

What is the difference between these two types?

data Data a = Data !a
newtype Newtype a = Newtype a

(Note: Bangs in data definitions are standard Haskell.)

Overflowing with foldl'

foldl' (+) (0 :: Int) [1..100000] – in what way can a sufficiently stupid compiler overflow here?

Pest or Cholera?

Does foldr (+) (0 :: Int) overflow the heap or the stack? What about foldl (+) (0 :: Int)?