On Mon, Nov 3, 2008 at 4:58 PM, minh thu <[EMAIL PROTECTED]> wrote: > Hi, > > Given a TypeRep and a Dynamic value with type corresponding to the > TypeRep, I'd like to be able to use fromDyn *without* specifying a type > (given as an additional 'default' argument) (since it is somewhat known > from the TypeRep). > > That is, I'd like an undefinedOf that can be used in > > extract :: Typeable a => TypeRep -> Dynamic -> a > extract typerep dyn = fromDyn (undefinedOf typerep) dyn > > For instance, if TypeRep is Int, > extract Int dyn = fromDyn (undefined::Int) dyn > > Is it possible to write "extract" ? >
Yep! It's already written: fromDynamic :: Typable a => Dynamic -> Maybe a It returns Nothing if the Dynamic value was of the wrong type. See: http://haskell.org/ghc/docs/latest/html/libraries/base/Data-Dynamic.html#v:fromDynamic -Antoine _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
