[Haskell-cafe] why are implicit types different? (cleanup)

Simon Peyton-Jones simonpj at microsoft.com
Mon Nov 27 06:43:55 EST 2006


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.

Simon

| -----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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