substituteChar :: Char -> Char
substituteChar c =
  case c of 
    'e' -> '3'
    'o' -> '0'
    'a' -> '4'
    't' -> '7'
    _ -> c
substituteChar :: Char -> Char
substituteChar c =
  case c of 
    'e' -> '3'
    'o' -> '0'
    'a' -> '4'
    't' -> '7'
    _ -> c
substituteChar c =
  case c of 
    'e' -> '3'
    'o' -> '0'
    'a' -> '4'
    't' -> '7'
    _ -> c