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?)
Hi Neil, thanks for the response. On Mon, May 30, 2011 at 8:48 PM, Neil Mitchell ndmitch...@gmail.com 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?)
From: Neil Mitchell ndmitch...@gmail.com 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
