Function to output function name

Question

Is it possible in Haskell to implement a function which returns its own function name?

A possible type could be (a -> b) -> String.

Answer 1

I don't know what you need it for, but maybe a simplistic solution suffices? Like so:

data NamedFunction a b = NamedFunction { 
    name :: String,
    apply :: a -> b
}

timesTwo :: NamedFunction Int Int
timesTwo = NamedFunction "timesTwo" (\x -> 2 * x)

which you can use as follows:

ghci> timesTwo `apply` 7
14
ghci> name timesTwo
"timesTwo"

You can then write your own version of (.):

-- contrast (.)  ::    (b -> c) ->          (a -> b) ->         (a -> c)
compose :: NamedFunction b c -> NamedFunction a b -> NamedFunction a c
compose (NamedFunction n1 f1) (NamedFunction n2 f2) = 
     NamedFunction (n1++ " . " ++ n2) (f1 . f2)

In ghci:

ghci> let f = timesTwo `compose` timesTwo in (f `apply` 7, name f) 
(28,"timesTwo . timesTwo")

You'll have to reimplement your own versions of map, filter and so on, and you're bound to run into other problems later, but maybe this is all you need...