Alright, updated it to extract EData from the Event type and make it separate. Basically, now all type signatures
Event a Widget a Behaviour a should read Event [EData a] Widget [EData a] Behaviour [EData a] for backward compatibility. On Thu, Apr 2, 2009 at 11:53 AM, Jeff Heard <jefferson.r.he...@gmail.com> wrote: > On Thu, Apr 2, 2009 at 11:22 AM, Jules Bean <ju...@jellybean.co.uk> wrote: >> >> Maybe I wasn't clear, and probably I'm being dense. I understand what you've >> done - I looked at the type declarations before commenting - but I don't >> understand why. >> >> Why is it useful to be able to use basic types without locking down 'a'? >> >> Why is it useful to have a value of type "Event FooBar" which, in apparent >> defiance of the FooBar parameter, actually contains a value of type Double? >> >> Jules >> > > I'm assuming everyone won't want to start from scratch in creating all > their widgets and behaviours. A bus contains only events of type 'a', > therefore all widgets and behaviours on that bus must use events of > type 'a'. It is possible to run multiple buses at the same time in > the same program, and even possible to have them communicate between > each other (forkIO-ing the buses and attaching some arbitrary > behaviour that takes events from bus0, translates their types and then > puts them on bus1), and so that way you could use multiple types, but > I don't see a problem with a user having to read the documentation and > understand that an Event of type a contains data that is a variant > including type a. How is it useful? Consider the following widgets: > > commandLineArgsWidget :: Widget a > commandLineArgsWidget = getArgs >>= > \args -> produce' "Environment" > "CommandLineArgsWidget" > "argv" > Persistent > [EStringL args] > > environmentWidget :: Widget a > environmentWidget b = getEnvironment >>= > mapM_ (\(k,v) -> produce' "Environment" "EnvironmentWidget" k > Persistent [EString v] b) > > progNameWidget :: Widget a > progNameWidget b = getProgName >>= > \v -> produce' "Environment" "ProgramNameWidget" "ProgramName" > Persistent [EString v] b > > As the library stands right now, I can take these widgets and put them > in a module and include them as part of the Buster library, and they > can be used pretty arbitrarily. I can see being more semantically > pure and changing Event a to contain data of type a instead of data of > type [EData a], in which case the type signatures would look like > this: > > progNameWidget :: WIdget [EData a] > > and so forth to be compatible with Bus [EData a], but I think that in > the end so many widgets will reuse the EData type that it's just as > well to make it part of the Event rather than force the user to be > explicit about it every time. But if I'm generally disagreed with > about this, I can change it -- I'm pretty neutral about it, to be > honest. > > -- Jeff > _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
