Show Both in Haskell (cf. https://gist.github.com/Qqwy/e092a68d508268f0f25cb5d1ffb3ad72)

ShowBoth.hs

{-# LANGUAGE TypeFamilies          #-}
{-# LANGUAGE DataKinds             #-}
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE FlexibleInstances     #-}
{-# LANGUAGE FlexibleContexts      #-}
{-# LANGUAGE ScopedTypeVariables   #-}

module ShowBoth where

import Data.Proxy

type family IsTuple (a :: *) :: Bool where
  IsTuple (a, b) = 'True
  IsTuple a      = 'False

class ShowBoth (a :: *) (b :: Bool) where
  showBoth :: Proxy b -> a -> String

instance (Show a, Show b) => ShowBoth (a, b) 'False where
  showBoth _ (a, b) = concat
    [ "The first element is: `"
    , show a
    , "` and the second element is: `"
    , show b
    , "`"
    ]

instance (Show a, Show b) => ShowBoth (a, (b, c)) 'True where
  showBoth _ (a, (b, _)) = concat
    [ "The first element is: `"
    , show a
    , "` and the second element is: `"
    , show b
    , "`"
    ]

showBoth' :: forall a b. ShowBoth (a, b) (IsTuple b) => (a, b) -> String
showBoth' = showBoth (Proxy :: Proxy (IsTuple b))