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List of polymorphic functions in haskell?

Consider the code below:

t1 :: [Int] -> (Int,String)
t1 xs = (sum xs,show $ length xs)

t2 :: [Int] -> (Int,String)
t2 xs = (length xs, (\x -> '?') <$> xs)

t3 :: [Int] -> (Char,String)
t3 (x:xs) = ('Y',"1+" ++ (show $ length xs))
t3  []     = ('N',"empty")

These three functions are of a type that only partially changes — they are fully usable without the need to know the type of the first component of the tuple that they produce. This means that I can work with them without having to refer to this type:

fnListToStrs vs fs = (\x -> snd $ x vs) <$> fs

Loading these definitions into GHCi, all three functions work independently as an argument fnListToStrs, and indeed I can pass a list containing both t1 and t2, because they are of the same type:

*Imprec> fnListToStrs [1,2] [t1,t2]
["2","??"]
*Imprec> fnListToStrs [1,2] [t3]
["1+1"]

But I can not pass all 3 at the same time, although the type discrepancy is actually not related to the calculations performed:

*Imprec> fnListToStrs [1,2] [t1,t2]
["2","??"]
*Imprec> fnListToStrs [1,2] [t3]
["1+1"]

, - , , , fnListToStrs , :

fnListToStrs :: [Int] -> [forall a.[Int]->(a,String)] -> [String]

?

+4
2

- , . Haskell , ...

{-# LANGUAGE GADTs #-}

data SomeFstRes x z where
  SFR :: (x -> (y,z)) -> SomeFstRes x z

> fmap (\(SFR f) -> snd $ f [1,2]) [SFR t1, SFR t2, SFR t3]
["2","??","1+1"]

. , :

> fmap ($[1,2]) [snd . t1, snd . t2, snd . t3]
["2","??","1+1"]
+3

"" . -

wrap :: (a -> (b, c)) -> a -> c
wrap f = snd . f

( ), , , , .

, - . ,

data Blob a b = Blob [a -> b] [a]

, Blob a b, b, a. ,

data WrapBlob b where
  WrapBlob :: Blob a b -> WrapBlob b

, (), .

+3

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