[Haskell-cafe] Where does ~> come from?
David Menendez
dave at zednenem.com
Wed Feb 20 00:34:24 EST 2008
On Feb 19, 2008 4:15 PM, Wolfgang Jeltsch <g9ks157k at acme.softbase.org> wrote:
> Am Dienstag, 19. Februar 2008 18:26 schrieben Sie:
> > […]
>
> > However, I was told this: ~> a b is a ~> b, but if I write c a b and
> > wish the effect of a `c` b. This would not work. ~> as an infix operator
> > has a special place in GHC. It is not "just a type variable".
>
> Sorry, but I don't understand fully what you mean. :-( But nevertheless,
> a ~> b is not the same as ~> a b but as (~>) a b. It's just like with
> ordinary operators where a + b is the same as (+) a b.
Note that some (all?) versions of GHC will incorrectly print "a ~> b"
as "~> a b".
<http://hackage.haskell.org/trac/ghc/ticket/1930>
Prelude> :t undefined :: a + b
undefined :: a + b :: forall (+ :: * -> * -> *) a b. + a b
It mostly gets infix type constructors right, although there are
apparently problems with precedence and associativity.
--
Dave Menendez <dave at zednenem.com>
<http://www.eyrie.org/~zednenem/>
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