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• GHC 6.12 and MacPorts

  - by absz

  I recently installed GHC 6.12 and the Haskell Platform 2010.1.0.1 on my Intel MacBook running OS X 10.5.8, and initially, everything worked fine. However, I discovered that if I use cabal install to install a package which depends on a MacPorts library (e.g., cabal install --extra-lib-dirs=/opt/local/lib --extra-include-dirs=/opt/local/include gd), things work fine in GHCi, but if I try to compile, I get the error Linking test ... Undefined symbols: "_iconv_close", referenced from: _hs_iconv_close in libHSbase-4.2.0.0.a(iconv.o) "_iconv", referenced from: _hs_iconv in libHSbase-4.2.0.0.a(iconv.o) "_iconv_open", referenced from: _hs_iconv_open in libHSbase-4.2.0.0.a(iconv.o) ld: symbol(s) not found collect2: ld returned 1 exit status After some Googling, I found a long Haskell-cafe thread discussing this problem. The upshot seems to be that MacPorts installs an updated version of libiconv, and the binary interface is slightly different from the version included with the system. Consequently, if you try to link with any MacPorts library, the MacPorts libiconv gets linked in too; and since the base library was built to link against a different version of libiconv, things break. I've tried setting LD_LIBRARY_PATH and DYLD_LIBRARY_PATH and adding more flags to try to get it to look at /usr/lib again (e.g. cabal install --extra-lib-dirs=/opt/local/lib --extra-include-dirs=/opt/local/include --extra-lib-dirs=/usr/lib --extra-include-dirs=/usr/include gd), but neither worked. Uninstalling the MacPorts libiconv isn't really an option, since I have a bunch of ports installed which depend on it---including some ports I want Haskell to link to, like gd2. From what I've seen online, the upshot really seems to be "you're boned": you cannot link against any MacPorts library while compiling with GHC, and there doesn't seem to be a solution. However, that thread was from the end of 2009, so I figure there's a chance that someone has a solution, workaround, ridiculous hack… anything, really. So: does anybody know how to get GHC 6.12 to link against the system libiconv at the same time as it links to libraries from MacPorts? Or, failing that, a way to make linking not break in some other clever way?

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• Image drawing library for Haskell?

  - by absz

  I'm working on a Haskell program for playing spatial games: I have a graph of a bunch of "individuals" playing the Prisoner's Dilemma, but only with their immediate neighbors, and copying the strategies of the people who do best. I've reached a point where I need to draw an image of the world, and this is where I've hit problems. Two of the possible geometries are easy: if people have four or eight neighbors each, then I represent each one as a filled square (with color corresponding to strategy) and tile the plane with these. However, I also have a situation where people have six neighbors (hexagons) or three neighbors (triangles). My question, then, is: what's a good Haskell library for creating images and drawing shapes on them? I'd prefer that it create PNGs, but I'm not incredibly picky. I was originally using Graphics.GD, but it only exports bindings to functions for drawing points, lines, arcs, ellipses, and non-rotated rectangles, which is not sufficient for my purposes (unless I want to draw hexagons pixel by pixel*). I looked into using foreign import, but it's proving a bit of a hassle (partly because the polygon-drawing function requires an array of gdPoint structs), and given that my requirements may grow, it would be nice to use an in-Haskell solution and not have to muck about with the FFI (though if push comes to shove, I'm willing to do that). Any suggestions? * That is also an option, actually; any tips on how to do that would also be appreciated, though I think a library would be easier.

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