On Mon, Mar 01, 2021 at 05:45:07PM +0100, Johannes Waldmann wrote:
I've developed a horror of reading and writing "length something :: Int".
If you're willing to tolerate the small overhead of Natural: $ ghci λ> import Data.Foldable (Foldable, foldl') λ> import GHC.Natural λ> len :: Foldable t => t a -> Natural; len = foldl' (\a _ -> a + 1) 0 λ> let x = len [1,2,3] λ> :t x x :: Natural λ> x 3 otherwise, note that `succ`, unlike (+), does bounds checks: λ> let x = maxBound :: Int λ> succ x *** Exception: Prelude.Enum.succ{Int}: tried to take `succ' of maxBound and so: λ> import Data.Foldable (Foldable, foldl') λ> len :: Foldable t => t a -> Int; len = foldl' (\a _ -> succ a) 0 λ> let x = len [1,2,3] λ> :t x x :: Int λ> x 3 on a 64-bit machine, testing to make sure the bounds check actually works would take too long, but we can cheat: λ> len :: Foldable t => t a -> Int; len = foldl' (\a _ -> succ a) (maxBound :: Int) λ> len [] 9223372036854775807 λ> len [1] *** Exception: Prelude.Enum.succ{Int}: tried to take `succ' of maxBound -- Viktor.