At 5:24 PM +0200 7/31/98, Christian Sievers wrote:
>Hello,
>
>I'd like to see example uses of hugs 1.3c's rank 2 polymorphism that
>are a bit more usefull than the amazing functions amazed and twice
>from the WhatsNew file. I am also interested in functions that one
>would like to define, but can't because of the restrictions in hugs
>1.3c. Why are they there? Are there implementations of languages with
>more general type systems? Finally, I'd like to get references to the
>theory behind rank 2 polymorphism and existential types.
>
>Thank you,
>Christian Sievers
In my error correcting parser combinators I use the type:
newtype RealParser s a = P (forall b d
. (b -> Errs s -> [s] -> Steps d)
-> (a -> b)
-> Errs s
-> [s] -> Steps d
)
, which is interesting in the sense that it is quantified over more than
one variable.
For an explanation of the type you may read:
http:/www.cs.uu.nl/groups/ST/Software/Parse/Sofsem99.pdf
Such a type typically arises when you write programs in a continuation
based style.
Doaitse Swierstra
__________________________________________________________________________
S. Doaitse Swierstra, Department of Computer Science, Utrecht University
P.O.Box 80.089, 3508 TB UTRECHT, the Netherlands
Mail: mailto:[EMAIL PROTECTED]
WWW: http://www.cs.uu.nl/
PGP Public Key: http://www.cs.uu.nl/people/doaitse/
tel: +31 (30) 253 3962, fax: +31 (30) 2513791
__________________________________________________________________________
