It compiles fine :-) If you want, you can take a look at this [1] version of the code (or the tarball [2]).
Load Main.hs in GHCi and run `test`, it will evaluate to `True`. Then, in the source code, switch the type of `test` from `P.Bool` to `Js JsBool` (in the comments) and run `test` again, now it will evaluate to a JavaScript expression. The code is still very immature (basically only that one example works), but it demonstrates our intend. - Tom [1]: http://github.com/tomlokhorst/AwesomePrelude/tree/master [2]: http://github.com/tomlokhorst/AwesomePrelude/tarball/master On Tue, Jun 30, 2009 at 8:21 PM, Conal Elliott<co...@conal.net> wrote: > Does this code compile? I'd expect that > > instance Bool (Js JsBool) (Js r) where > > violates the fundep, since it applies for *all* values of r, not just to > one. > > - Conal > > On Tue, Jun 30, 2009 at 8:53 AM, Sebastiaan Visser <sfvis...@cs.uu.nl> > wrote: >> >> On Jun 30, 2009, at 5:24 PM, Conal Elliott wrote: >>> >>> Hi Sebastiaan, >>> >>> I like your extensions of generalized booleans to other common Haskell >>> types! >>> >>> I also prefer using type families to fundeps. In this case I didn't >>> because of some awkwardness with vector operations, but I'm going to try >>> again. >>> >>> I'm confused about your particular fundep choice. For instance, >>> >>> class Bool f r | f -> r where >>> bool :: r -> r -> f -> r >>> false :: f >>> true :: f >>> >>> Do you *really* mean that the boolean type f determines the value type r? >> >> Yes, that is really what I mean. This can be used to enforce that the >> return value of elimination can be restricted by the boolean type. This is >> especially useful when using GADTs to encode your domain language. >> >> For example, take this simple JavaScript language: >> data Js a where >> Prim :: String -> Js a -- Primitive embedding. >> App :: Js (a -> b) -> Js a -> Js b -- Function application. >> >> data JsBool >> >> Now the functional dependencies can be used to enforce that eliminating >> booleans in the Js domain always returns a value in the Js domain: >> instance Bool (Js JsBool) (Js r) where >> bool f t c = Prim "(function ifthenelse (f, t, c) c ? t : f)" `App` f >> `App` t `App` c >> true = Prim "true" >> false = Prim "false" >> Getting rid of this fundep and using type families will probably be a lot >> more intuitive. >> >> Any suggestions on how to enforce elimination to be able to go from `Js >> JsBool -> Js r' using other techniques? >>> >>> Regards, - Conal >>> >>> ... >> >> -- >> Sebastiaan Visser >> >> >> > > > [] > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe@haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > > _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
