haskell - Why does ghci desugar type lists and type families? Can this be selectively disabled? -

i'm trying make types ghci displays libraries intuitive possible, i'm running lot of difficulties when using more advanced type features.

let's have code in file:

{-# language typefamilies #-} {-# language datakinds #-} {-# language typeoperators #-}  import ghc.typelits  data container (xs::[*]) = container 

i load in ghci, type following command:

ghci> :t undefined :: container '[string,string,string,string,string] 

unfortunately, ghci gives me rather ugly looking:

:: container        ((':)           *           string           ((':)              * string ((':) * string ((':) * string ((':) * string ('[] *)))))) 

ghci has removed sugar type level strings. there way prevent ghci doing , giving me pretty version?

---

on related note, lets create type level replicate function

data nat1 = 0 | succ nat1  type family replicate (n::nat1) x :: [*] type instance replicate 0 x = '[] type instance replicate (succ n) x = x ': (replicate n x)  type lotsofstrings = replicate (succ (succ (succ (succ (succ zero))))) string 

now, when ask ghci type using lotsofstrings:

ghci> :t undefined :: container lotsofstrings 

ghci nice , gives me pretty result:

undefined :: container lotsofstrings 

but if ask replicated version,

ghci> :t undefined :: container (replicate (succ (succ (succ (succ (succ zero))))) string) 

ghci substitutes in type family when didn't type synonym:

:: container        ((':)           *           [char]           ((':)              * [char] ((':) * [char] ((':) * [char] ((':) * [char] ('[] *)))))) 

why ghci doing substitution type family, not type synonym? there way control when ghci substitution?

the workaround know of using :kind. instance,

ghci> :kind (container '[string,string,string,string,string])

gives:

( container '[string,string,string,string,string]) :: *

while

ghci> :kind! (container '[string,string,string,string,string])

will print this:

container

((':)

  *   [char]   ((':)      * [char] ((':) * [char] ((':) * [char] ((':) * [char] ('[] *)))))) 

officially, of course, you're asking ghci different question kind, works. using undefined :: sort of workaround anyhow, thought might suffice.