give equal rights to types and classes! :)

Philippa Cowderoy flippa at
Thu Feb 2 16:11:35 EST 2006

On Thu, 2 Feb 2006, Taral wrote:

> On 2/2/06, Philippa Cowderoy <flippa at> wrote:
> > Not in the context of a predicative type system. Also, if we treat it
> > simply as an annotation (exists a . a), we end up throwing away the
> > additional information inferred.
> There's that word again. Can someone explain what "predicative" means,
> in detail?

For historical reasons that's hard work. The short version is "type 
variables can only be instantiated to monotypes", whereas in an 
impredicative system type variables can be instantiated to types including 

flippa at

'In Ankh-Morpork even the shit have a street to itself...
 Truly this is a land of opportunity.' - Detritus, Men at Arms

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