Job Vranish
Its main advantages are: Very easy to use. Almost entirely Haskell98 (the non Haskell98 pieces are not critical, just nice) The datatype is a member of Foldable, Traverable, Applicative, Monad, etc... Then length of the list is encoded in the type in a natural way.
Unfortunately, it's very easy to get a context reduction stack overflow from GHC this way, which makes using such datatypes awkward for anything but very short lists. Explicit type annotations will often make things work, but at that point the type class isn't helping you anyway. For example, assuming the default stack size: import Data.FixedList fixed18 :: FixedList18 Int fixed18 = fromFoldable' [1..] -- this works fixed20 = 20 :. 20 :. fixed18 -- this works fixed22 :: FixedList22 Int fixed22 = 22 :. 22 :. fixed20 -- this only works with a type annotation show18 = show fixed18 -- this works -- this doesn't work: -- show20 = show fixed20 show20' :: FixedList20 Int -> String show20' list20 = show list20 show20 = show20' fixed20 -- this does work Using head and tail on longer lists fails likewise. I expect there's some way to make it work without simply increasing the stack depth, but I'm not sure how. Any thoughts? - C.