Re: [Haskell-cafe] uniplate (was: code review?)
Hi Neil, thanks for the response. On Mon, May 30, 2011 at 8:48 PM, Neil Mitchell wrote: > Hi John, > > >> > While I'm on the topic, I recently wrote a tool that wanted to > >> > traverse deep data structures as produced by haskell-src-exts. ?I > >> > wound up with about 50 lines of case expressions and around the time > >> > my hands were literally beginning to hurt decided that enough was > >> > enough and I should try a generic approach. ?I heard uniplate was > >> > pretty easy to use, and was pretty pleased to turn the entire thing > >> > into a single line. ?It took me a little longer to figure out I needed > >> > to use universeBi since all the examples were monotyped, but once I > >> > did it Just Worked. ?Amazing. ?So thanks again! ?And maybe you could > >> > mention universeBi in the instant introduction? > >> > >> Yes, I probably should - I'll try and get to that. Of course, I'd also > >> happily accept a patch against > >> http://community.haskell.org/~ndm/darcs/uniplate > >> > >> I use Uniplate inside HLint, and it's invaluable - there are a lot of > >> times when List Comp + universeBi really hits the spot. > > > > Does Uniplate include an instance for: > >> instance Uniplate a => Biplate [a] a > > No, it only includes: > > instance Biplate [Char] Char where >biplate (x:xs) = plate (:) |* x ||* xs >biplate x = plate x > > I am slightly curious why I didn't include the more general a instead > of Char version, but perhaps it doesn't quite work - polymorphic > versions of the Direct instances can have problems if you pick weird > types. I'll have a think, and if it does always work, I'll include it. > > Note that if you use the Typeable or Data versions this instance is > automatically available. In practice I almost always end up using the > Data versions of Uniplate, they require no instance definitions are > are good to get started with - you can switch to Direct only if you > need the additional performance. > I started with Data, but writing the Direct instance was so simple that I didn't see a reason not to do it. My type doesn't have many constructors yet though, and several of them aren't recursive, so maybe it was easier than normal. John ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] uniplate (was: code review?)
Hi John, >> > While I'm on the topic, I recently wrote a tool that wanted to >> > traverse deep data structures as produced by haskell-src-exts. ?I >> > wound up with about 50 lines of case expressions and around the time >> > my hands were literally beginning to hurt decided that enough was >> > enough and I should try a generic approach. ?I heard uniplate was >> > pretty easy to use, and was pretty pleased to turn the entire thing >> > into a single line. ?It took me a little longer to figure out I needed >> > to use universeBi since all the examples were monotyped, but once I >> > did it Just Worked. ?Amazing. ?So thanks again! ?And maybe you could >> > mention universeBi in the instant introduction? >> >> Yes, I probably should - I'll try and get to that. Of course, I'd also >> happily accept a patch against >> http://community.haskell.org/~ndm/darcs/uniplate >> >> I use Uniplate inside HLint, and it's invaluable - there are a lot of >> times when List Comp + universeBi really hits the spot. > > Does Uniplate include an instance for: >> instance Uniplate a => Biplate [a] a No, it only includes: instance Biplate [Char] Char where biplate (x:xs) = plate (:) |* x ||* xs biplate x = plate x I am slightly curious why I didn't include the more general a instead of Char version, but perhaps it doesn't quite work - polymorphic versions of the Direct instances can have problems if you pick weird types. I'll have a think, and if it does always work, I'll include it. Note that if you use the Typeable or Data versions this instance is automatically available. In practice I almost always end up using the Data versions of Uniplate, they require no instance definitions are are good to get started with - you can switch to Direct only if you need the additional performance. Thanks, Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] uniplate (was: code review?)
> > From: Neil Mitchell > > > While I'm on the topic, I recently wrote a tool that wanted to > > traverse deep data structures as produced by haskell-src-exts. ?I > > wound up with about 50 lines of case expressions and around the time > > my hands were literally beginning to hurt decided that enough was > > enough and I should try a generic approach. ?I heard uniplate was > > pretty easy to use, and was pretty pleased to turn the entire thing > > into a single line. ?It took me a little longer to figure out I needed > > to use universeBi since all the examples were monotyped, but once I > > did it Just Worked. ?Amazing. ?So thanks again! ?And maybe you could > > mention universeBi in the instant introduction? > > Yes, I probably should - I'll try and get to that. Of course, I'd also > happily accept a patch against > http://community.haskell.org/~ndm/darcs/uniplate > > I use Uniplate inside HLint, and it's invaluable - there are a lot of > times when List Comp + universeBi really hits the spot. > Does Uniplate include an instance for: > instance Uniplate a => Biplate [a] a ? Since lists are a common case, I was surprised that this instance wasn't included. Is there a reason it shouldn't exist? I was importing Data.Generics.Uniplate.Direct FWIW. Thanks, John Lato ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
