If ∷ Bool → ReadP α → ReadP α
readParensIf p x = if p then mandatory
              else (x +++ mandatory)
    where mandatory = between (char '(') (char ')') x

showParensIf ∷ B
readParensIf ∷ Bool → ReadP α → ReadP α
readParensIf p x = if p then mandatory
              else (x +++ mandatory)
    where mandatory = between (char '(') (char ')') x
readParensIf p x = if p then mandatory
              else (x +++ mandatory)
    where mandatory = between (char '(') (char ')') x