ShowFn.hs

instance (Num a, Show a) => Show (FnShow a) where
  show (FnShow1 fnStr fn) =
    concat (map showFn [0, 1, 2, 3, 4, 5, 6, 7, 8, 9])
    where showFn n = fnStr ++ " " ++ show n ++ " = " ++ show (fn n) ++ "\n"
  show (FnShow2 fnStr fn) =
    concat (map showOp [0, 1, 2, 3])
    where showOp n = show (FnShow1 (fnStr ++ " " ++ show n) (fn n))
  show (FnShow3 fnStr fn) =
    concat (map showOp [0, 1, 2, 3])
    where showOp n = show (FnShow2 (fnStr ++ " " ++ show n) (fn n))
  show (OpShow1 fnStr fn) =
    concat (map showOp [0, 1, 2, 3, 4, 5, 6, 7, 8, 9])
    where showOp n = show n ++ " " ++ fnStr ++ " = " ++ show (fn n) ++ "\n"
  show (OpShow2 fnStr fn) =
    concat (map showOp [0, 1, 2, 3])
    where showOp n = show (FnShow1 (show n ++ " " ++ fnStr) (fn n))

data FnShow a = FnShow1 String (a -> a)
              | FnShow2 String (a -> a -> a)
              | FnShow3 String (a -> a -> a -> a)
              | OpShow1 String (a -> a)
              | OpShow2 String (a -> a -> a)

sqr x = x * x

abc a b c = a * b - c

main = do
  print $ FnShow3 "abc"  abc
  print $ OpShow2 "+"    (+)
  print $ FnShow2 "mul"  (*)
  print $ FnShow1 "sqrt" sqrt
  print $ OpShow1 "+ 2"  (+2)
  print $ FnShow1 "sqr"  sqr