Tomáš Janoušek
Hello,
On Thu, Mar 19, 2009 at 05:49:34PM -0600, Duane Johnson wrote:
I'm not sure I understand what is going on here, but it seems to me that the following assignment of "mult = (*)" causes "mult" to lose out on some of the polymorphic behavior of (*). Is that right? If so, why?
This is the monomorphism restriction kicking in.
See http://www.haskell.org/haskellwiki/Monomorphism_restriction.
Prelude> let (...) = (*) Prelude> :t (...) (...) :: Integer -> Integer -> Integer
Prelude> :set -fno-monomorphism-restriction Prelude> let (...) = (*) Prelude> :t (...) (...) :: (Num a) => a -> a -> a
I believe it is a good practice to always write the function type.
Prelude> let mult :: Num a => a -> a -> a ; mult = (*) Prelude> :i mult mult :: (Num a) => a -> a -> a -- Defined at <interactive>:1:35-38 -- c/* __o/* <\ * (__ */\ <