[Haskell-cafe] why are implicit types different? (cleanup)
S. Alexander Jacobson
alex at alexjacobson.com
Mon Nov 27 11:21:51 EST 2006
Ok, I'm not sure I understand the answer here, but how about a
workaround. My current code looks like this:
tt = let ?withPassNet=wpn
in passNet "passnet" ["user"] regImpl b
The type of wpn is:
wpn :: Ev PassNet ev a -> Ev State ev a
The individual implicit parameters end up arriving with concrete
values for a. If I pass wpn to passNet explicitly, it also appears to
get converted to a monotype on arrival at the inside of passNet.
So I guess the real question is, how do I pass a polytype* wpn?
* I would have thought the word was polymorphic, but you obvoiusly
S. Alexander Jacobson tel:917-770-6565 http://alexjacobson.com
On Mon, 27 Nov 2006, Simon Peyton-Jones wrote:
> Implicit parameters have monotypes, not polytypes. So ?f in g gets
> type (Char->Char). I rather doubt that something more general
> (implicit parameters get polytypes) would work, given the implicit
> "improvement" rules that implicit parameters require.
> | -----Original Message-----
> | From: haskell-cafe-bounces at haskell.org [mailto:haskell-cafe-bounces at haskell.org] On Behalf Of S.
> | Alexander Jacobson
> | Sent: 21 November 2006 19:28
> | To: haskell-cafe at haskell.org
> | Subject: [Haskell-cafe] why are implicit types different? (cleanup)
> | Why do g and g' have different types?
> | g x y = let ?f = \x-> x in ?f x ++ (show (?f y))
> | g :: [Char] -> [Char] -> [Char]
> | g' :: (Show t) => [Char] -> t -> [Char]
> | g' x y = let f = \x-> x in f x ++ (show (f y))
> | Is there a way I can use implicit types and let g be as general as g'?
> | -Alex-
> | ______________________________________________________________
> | S. Alexander Jacobson tel:917-770-6565 http://alexjacobson.com
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