On Mon, May 12, 2014 at 11:44 AM, Venu Chakravorty <c.venu@aol.com> wrote:
Prelude> :t (+)
(+) :: (Num a) => a -> a -> a
What I understand from the above is that "+" is a function that takes two args
which are types of anything that IS-AN instance of "Num" (Int, Integer, Float, Double)
and returns an instance of "Num".
Not exactly. It says that, given some type a that is an instance of Num, it will add two values of that type and produce a new value of that same type. You cannot mix and match types; it always works on some specific type, although those types may change between uses of (+).
This is somewhat hidden by the way numeric literals are handled: a literal without a decimal point is handled as if you had wrapped it in fromIntegral, and one with a decimal point is handled as if you had wrapped it in fromRational.