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glasgow-haskell-users@haskell.org

July 2009

41 participants
32 discussions

How to save a haskell data structure in C?
by Shu Wu 03 Jul '09

03 Jul '09

Hey, folks. I've got a problem which I've thought about for days. I need to write a program that mixes C and haskell code. And the C code controls the procedure. In C code, I want to save a complex data strcuture defined in haskell and pass it back to a haskell function at certain time. Like the following: in haskell: data A = A {...} -- very very complex data structure initA :: A initA = A {...} func :: A -> A func a = ... -- return a new 'A' in C: main { a = initA ... take some actions a = func a; ... take some other actions a = func a; ... ... } Different from most cross-language programs, this C program doesn't alter the data in haskell, just saves it and passes it on. So I'm wondering if there's some convienent way other than marshalling the data in haskell? BTW, mashalling data requires all work done in IO monad, which will change the program stucture. So I really don't want to mashal it. Thank you!

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better generation of vi ctags in ghci
by Peter Hercek 02 Jul '09

02 Jul '09

Hi GHC and VI users, I got frustrated with vi tags not working after some unrelated code is edited in a source file. Moreover non-exported top level declarations were not available in vi tags file. Here is an attempt to fix it: http://www.hck.sk/users/peter/pub/ghc/betterCTags.patch Why would you want the new implementation of :ctags ghci command? * Tags are searched based on the line content. This is what Exuberant Ctags do for other languages and it is the other posix way to do it. This makes the positioning to work well even when the source code was edited (on places unrelated to the tag location). More complicated Ex statements can be used to improve it even more but then it does not work well with :tselect (it screws up tag kinds, at least with my version of vim 7.2.65). * All top level symbols defined in a module are added to the tags file. Even the non-exported ones. These are marked as static (file:) so the default tag selection (Ctrl-]) works fine based on the file you started the search from. * Tags get kinds added so you can select whether you want to get to a type constructor or a data constructor (that is if you share names between the two). * In general it is a nice addition to vim haskellmode. If you search for help on symbols in libraries then opening haddock is cool. If you search for help on a symbol in your project then opening the tag in a preview window (Ctrl-W} or ptselect) is cool. Problems: * It needs somebody to check that emacs tags were not broken. I'm not an emacs user but some tag generation code is shared for vim and emacs. I tried to keep emacs tags exactly the way they were (only the exported symbols, original file format). * If your code happens to have definitions on lines which happen to exist more times in one source file then it may put you at an incorrect location. I doubt it will ever happen but if anybody thinks it is really bad we can keep the original format of vim tags too. Then e.g. :ctags would generate tags with line numbers and :ctags! would generate tags with search expressions. If there is any support for this and ghc team decides to merge it I can provide darcs patch. I can do changes needed to get it merged. Peter.

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