To be honest I have totally paged that code out. I cvs log doesn't show the "massive perf bug" entry for either of the modules we specify, though I do vaguely remember something. My memory is that it shouldn't matter which way round you associate <> and <+>, but I could well be wrong about that. If anyone wants to dive in, please go ahead! (I don't think I'm likely to.) I do have somewhere a half-written paper about the internals of the HughesPJ library. Adding the 'empty' document and <+> were entirely non-trivial, and made my head hurt badly. Alas, I never finished the paper, but I'll hunt if someone wants it. Simon | -----Original Message----- | From: libraries-bounces@haskell.org [mailto:libraries-bounces@haskell.org] On Behalf Of Ian Lynagh | Sent: 04 March 2004 00:46 | To: libraries@haskell.org | Subject: Text.PrettyPrint.HughesPJ fixities | | | Hi, | | Text.PrettyPrint.HughesPJ (the same applies to | ghc/compiler/utils/Pretty.lhs) contains | | infixl 6 <> | infixl 6 <+> | infixl 5 $$, $+$ | | whereas my intuition says that infixr will give more efficient | implementation. Is my intuition wrong? It seems to be supported by the | definitions of hcat, hsep, vcat being defined in terms of foldr. | | | We on #haskell are also confused by the changelog entry starting | "Cured massive performance bug." and ending | "I'm not satisfied that I've done the best possible job. I'll send you | the code if you are interested.". | It looks to me like the change was made and the original mail about the | problem appended without being reread? | | | Thanks | Ian | | _______________________________________________ | Libraries mailing list | Libraries@haskell.org | http://www.haskell.org/mailman/listinfo/libraries