Re: [Haskell-beginners] how to feel free of the Implementation of Data structure

On Thu, Mar 24, 2011 at 06:34:57PM +0800, 吴兴博 wrote:

2. f1 :: (Integral a) => a -> String f2 :: (Integral a) => String -> a

pipe = f1 . f2 It is clear that pipe is String -> String,

Actually, this code will give an "ambiguous type" error, since the compiler cannot figure out what type 'a' should be. And the type that is chosen may make a difference for the behavior.

but.(1)How can I know what instance that 'a' is. (2)How can I determine what instance of 'a' is.

If you know what type you want to use for 'a' you can specify it with a type annotation, like this: pipe = f1 . (f2 :: String -> Int) -Brent