How to iterate over record fields?

Question

I have following datatype defined as record

data Config = Config
  { field1 :: String
  , field2 :: String
  , field3 :: String
  }

I want to iterate over each field of Config, apply some function String -> String, for example tail and get in return new Config.

What is idiomatic way to do this? Preferably, without heavy 3rd party libraries.

Answer 1

Well, the best way to do it would probably be

{-# LANGUAGE DeriveFunctor #-}

type Config = Config' String
data Config' a = Config
  { field1 :: a
  , field2 :: a
  , field3 :: a
  } deriving (Functor)

configHeads :: Config -> Config' Char
configHeads = fmap head