Alex Ferguson:
>Kevin Atkinson:
>> I take it that you are happy with names such as: [long list]
>
>Yes. Certainly I'm more than happy that types with completely different
>signatures have different names.
I also prefer to keep the names distinct when the meanings are distinct. I
got to thinking about zip and unzip, zip2 and unzip2, etc. which gave a
feeling of not being so distinct. Turns out, it's currying which prevents
their signatures from being combined. Non-curried versions can be defined
on general tuples, with just one pair of names:
class Zippable tOfLists tsInList
where
zip' :: tOfLists -> [tsInList]
unzip' :: [tsInList] -> tOfLists
instance Zippable () ()
where
zip' () = repeat ()
unzip' _ = ()
instance Zippable ([t],[u],[v]) (t,u,v)
where
zip' (x:xs, y:ys, z:zs) = (x,y,z): (zap (xs, ys, zs))
zip' _ = []
unzip' ((x,y,z):more) = (x:xs, y:ys, z:zs)
where
(xs, ys, zs) = unzip' more
instance Zippable ([t]) (t)
instance Zippable ([t],[u]) (t,u)
instance Zippable ([t],[u],[v],[w]) (t,u,v,w)
etc. left as an exercise.
Thus, the uglier cases on Kevin Atkinson's list can be addressed within
Haskell's current overloading system.
--
Scott Turner
[EMAIL PROTECTED] http://www.ma.ultranet.com/~pkturner
