Static library to redefine entrypoint
Dear GHCers, I am trying to write a wrapper library for lab work to give to students. My problem is, that the libraries I use require initialization that I really want to hide from our students. The wrapper I'm writing is compiled to a static library and installed with cabal, so students can just "ghc --make" or "ghci" their sources. Here comes the problem: I want to define main and let students just define labMain as an entry point to their program. How can I have my library use "labMain" without a definition? Keep in mind that I want to give them a cabalized library that they can just link to, so I can't give them a template file that they fill and compile together with my code. Is it at all possible to have "external" functions and letting the linker sort stuff out? Regards, Philip
Why not just tell them to import your library and do something like
main = withSomeInit labMain where "withSomeInit" is the function you provide? This approach is present in some other libs that require initialization.
Best regards
Christopher Skrzętnicki
On Fri, Apr 24, 2009 at 12:56, Philip K.F.
Dear GHCers,
I am trying to write a wrapper library for lab work to give to students. My problem is, that the libraries I use require initialization that I really want to hide from our students. The wrapper I'm writing is compiled to a static library and installed with cabal, so students can just "ghc --make" or "ghci" their sources. Here comes the problem: I want to define main and let students just define labMain as an entry point to their program.
How can I have my library use "labMain" without a definition? Keep in mind that I want to give them a cabalized library that they can just link to, so I can't give them a template file that they fill and compile together with my code. Is it at all possible to have "external" functions and letting the linker sort stuff out?
Regards, Philip
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On Fri, 2009-04-24 at 13:06 +0200, Krzysztof Skrzętnicki wrote:
main = withSomeInit labMain where "withSomeInit" is the function you provide? This approach is
Why not just tell them to import your library and do something like present in some other libs that require initialization.
Dear Christopher, I know there are alternatives and I know some people use them. A particular problem I have now, though, is SDL. On OS X, the SDL library defines an alternative entry-point to the application, called SDL_main, where the libSDL.a provides a main (insert long story about Cocoa frameworks and Objective-C linking here). I don't particularly like this method, but it's the world I have to work with. Also, many alternatives to SDL don't play nice with GHCi, which is particularly useful for lab teaching. If I can somehow introduce my own new entry point, I could also wrap GHCi in something else quite easily (I know I could wrap GHCi as it is, but it would be even nicer if I could just link to the binary). I figured this level of detail would distract form the question, though and I would run the risk that people would try to solve my SDL linking woes, which is not the point of the question. Regards, Philip
On Fri, 2009-04-24 at 12:56 +0200, Philip K.F. Hölzenspies wrote:
Dear GHCers,
I am trying to write a wrapper library for lab work to give to students. My problem is, that the libraries I use require initialization that I really want to hide from our students. The wrapper I'm writing is compiled to a static library and installed with cabal, so students can just "ghc --make" or "ghci" their sources. Here comes the problem: I want to define main and let students just define labMain as an entry point to their program.
How can I have my library use "labMain" without a definition? Keep in mind that I want to give them a cabalized library that they can just link to, so I can't give them a template file that they fill and compile together with my code. Is it at all possible to have "external" functions and letting the linker sort stuff out?
When I've set practicals like this I've just provided them with a 3 line Main module that imports functions exported by the module(s) that the students write. Eg I have them fill in Draw.lhs but tell them to compile the thing using ghc --make Main.hs. I never found that this confused any of them (indeed some were interested in looking at the code). Duncan
participants (3)
-
Duncan Coutts -
Krzysztof Skrzętnicki -
Philip K.F. Hölzenspies