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July 2010

54 participants
42 discussions

Containers and strictness
by Milan Straka 01 Jul '10

01 Jul '10

Hi, I am working on improving containers performance and have written a draft paper about it http://fox.ucw.cz/papers/containers/containers.pdf I wanted to start a new thread in response to strictness issues brought up by Claus Reinke. > - IntMap and Map expose different APIs wrt strictness > http://www.haskell.org/pipermail/libraries/2009-March/011399.html > http://www.mail-archive.com/haskell-cafe@haskell.org/msg48925.html > > - to work around the non-strict Map fold, users have to > resort to nested folds (non-strict fold to convert to list, > then strict foldl' over list) and other tricks: > http://www.haskell.org/pipermail/haskell-cafe/2010-June/079098.html > > similarly non-trivial thinking is required to work around other > no-control-over-strictness issues in the APIs, bypassing the obvious > functions and using non-obvious ones based on > knowledge about their implementation > > - strictness is used inconsistently: > http://hackage.haskell.org/trac/ghc/ticket/4109 > > - strictness is not documented: !!! > search for "strict" in the Data.Map/IntMap documentation.. > > this is really bad - the only way for users to become aware > of strictness problems is by running into them, and the only way to fix > strictness-related performance issues is by referring > to the implementation (in theory, an implementation change > could invalidate lots of performance fixes in production code) I need some opinion: - Do you think methods like insert/lookup/delete/etc should be strict in key/element? As Claus wrote, right now it is undocumented and inconsistent (both in the methods of one container and also in the same methods of different container). The problem is the following: a lookup on an empty container does not really have to evaluate the key. Should we honour it or should we sacrifice it to be faster and consistent with other methods (eg., insert has to be strict in the key). - The Set/Map, IntSet/IntMap do not currently have a strict fold. Do you think it should be added to the API? Cheers, Milan

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dirs in Emacs/Vim in Cabal
by Chris BROWN 01 Jul '10

01 Jul '10

Dear Haskellers, I am in the process of creating a cabal HaRe and I have run into a minor problem. I have an emacs and a vim script that HaRe uses to invoke the refactorer from the two editors. In those scripts, I point HaRe to a directory containing some libraries it needs to chase the imports of the modules. Cabal installs these libraries as data files into whatever prefix the user requests at install time. However, the problem I have is that it then requires a manual user intervention to manually configure emacs/vim to point to this new directory in the 'customizable' panel of HaRe. My question is: Is it possible to allow the emacs/vim scripts that I have know where this directory is automatically? I hope someone can help, Kindest regards, Chris Brown.

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