Question

I want to do something like this in Haskell, but the compiler is not letting me.

Is there any way to accomplish this task?

-- both modules export function named "hello"
-- and I want to run it in every module
import qualified MyMod as M1
import qualified MyAnotherMod as M2

runmodules = map (\m -> m.hello) [M1, M2]

Answer 1

I don’t think you can quote a qualified name prefix like that in template haskell, and the hello identifier isn’t in scope, so you might have to fall back to programming with strings.

module ModuleParamsTH where
import Language.Haskell.TH

getAll :: String -> [String] -> ExpQ
getAll valueName moduleNames = 
  listE $ map (varE . mkName . (++ suffix)) moduleNames
  where suffix = "." ++ valueName

which can then be used like so,

{-# LANGUAGE TemplateHaskell #-}
import ModuleParamsTH
import qualified ModuleParamsM1 as M1
import qualified ModuleParamsM2 as M2

runmodules = $(getAll "hello" ["M1", "M2"])

However, I would not do all this. You could just write [M1.hello, M2.hello] or use a type class to abstract over implementations.