Re: [Haskell-cafe] Where does ~> come from?

If ~> does not have any special meaning and it could be ### or xyz, then how does GHC know to print a ~> b, but not ~> a b a ### b, but not ### a b xyz a b, but not a `xyz` b Simply because xyz is alphanumeric? On Wed, Feb 20, 2008 at 12:34 AM, David Menendez wrote:

On Feb 19, 2008 4:15 PM, Wolfgang Jeltsch wrote:

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Am Dienstag, 19. Februar 2008 18:26 schrieben Sie:

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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 http://www.eyrie.org/~zednenem/

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