[Haskell-cafe] Polymorphic (typeclass) values in a list?

[Brandon S. Allbery KF8NH]

On Oct 19, 2007, at 12:11 , Sebastian Sylvan wrote:

> On 19/10/2007, Kalman Noel <kalman.noel at bluebottle.com> wrote:
>>
>>    data ExistsNumber = forall a. Num a => Number a
>
> I'm without a Haskell compiler, but shouldn't that be "exists a."?

The problem is that "exists" is not valid in either Haskell 98 or any  
current extension, whereas "forall" is a very common extension.  But  
you can simulate "exists" via "forall", which is the thrust of these  
approaches.

-- 
brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allbery at kf8nh.com
system administrator [openafs,heimdal,too many hats] allbery at ece.cmu.edu
electrical and computer engineering, carnegie mellon university    KF8NH