2008/11/4, Antoine Latter <[EMAIL PROTECTED]>: > 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
Well, it seems you can't really write (fromJust . fromDynamic) someDynamic without giving the type of what you expect. fromDynamic whould achieve the same thing I wrote in the previous mail if I did not write the ::Int on the right of undefined. (I would still have to write ::Int later in the code; that's what I'd like to avoid) Thanks, Thu _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
