In article <[EMAIL PROTECTED] ft.com>, "Simon Marlow" <[EMAIL PROTECTED]> wrote:
> I don't think we need more extensions to do a reasonable job of > extensible exceptions: > > http://www.haskell.org/~simonmar/papers/ext-exceptions.pdf You write: > Compared to our approach, theirs requires new extensions to the language > (although not deep), "Typeable" is an extension to Haskell, and a rather ugly one at that. The open datatypes extension is both cleaner and more general. > and has difficulties with separate compilation. They claim to solve this I think, though I haven't examined it really carefully. You may know better, of course. > Arguably the open data types approach is more direct and more accessible, Yes, > as is often the case with extensions designed to solve a particular problem. That's not fair. Open datatypes have other applications. A general "file interpreter" for instance, that given a MIME type string and a list of bytes yields an object. Or a collection of variable "resources" of various types that could be passed to a program. Or a hierarchy of UI widgets. Or anything that Typeable and Dynamic are currently used for, but more cleanly. Hs-plugins, for instance. It's the missing piece. > Still, the argument for adding open data types to the language is weakened by > the fact that they are subsumed by type classes: in fact the authors give an > encoding of open data types into type classes, Well not really. The "encoding" involves lifting everything from values to types, which means a function still can't return a value of an open type determined at run-time. -- Ashley Yakeley Seattle WA _______________________________________________ Haskell-prime mailing list Haskell-prime@haskell.org http://www.haskell.org/mailman/listinfo/haskell-prime
