Haskell, multiplying Int and Float within a function

Question

Why is it that in ghci I can enter:

5.0 * (3 - 1)
> 10.0

But if I try and create a function in a .hs file and load it in:

Answer 1

Your test function was more general, before you add a signature:

> let test a b c = a * (b - c)
> :t test
  test :: Num a => a -> a -> a -> a

You could restrict it, but all types must be the same:

test :: Fractional a => a -> a -> a -> a   -- some real types
test :: Integral   a => a -> a -> a -> a   -- all integer types
test :: Float -> Float -> Float -> Float  
test :: Int   -> Int   -> Int   -> Int   

test :: Int   -> Float -> Float -> Float  --wrong

By the way, 2 isn't Int and 0.2 isn't Float, let ask gchi:

> :t 2
 2 :: Num a => a
> :t 0.2
 0.2 :: Fractional a => a