On Sep 2, 2010, at 11:30 AM, michael rice wrote:

In each case, what does the notation

show:: ...

and

undefined:: ...

accomplish?

They're type annotations. show is a function in "many" types:

Prelude> :t show

show :: (Show a) => a -> String

If you want to see the type of a "specific" show function, you need to find a way to "determine" its type. This is a slightly different function, but it's equivalent in types and semantics:

Prelude> :t \x -> show x

\x -> show x :: (Show a) => a -> String

Now we have a named argument, and we can constraint its type with an annotation:

Prelude> :t \x -> show (x :: Int)

\x -> show (x :: Int) :: Int -> String