I have a haskell lib X having the following file-structure:
X/src/libxfiles.hs
X/default.nix
X/shell.nix
X/libx.nix
X/libx.cabal
X/cabal.project
and
X/example/lib/exampleCommon.hs
X/example/ex1/main.hs
X/example/ex2/main.hs
X/example/example.cabal
cabal.project points to libx.cabal and to example/example.cabal and cabal new-build all works inside nix-shell. The required haskell packages for libx library and example-programs are introduced in the libx.nix -file.
Why this structure? Since the example programs have 99% common code and only a couple of lines that are ui-dependend (webkit2gtk and such). Earlier version had flags and CPP inside the main of example and nix-build produced the lib and example prg in result-directory. On this new setup, the cabal new-build works ok when the compiler is ghc and my aim is to produce programs with ghc.
Earlier nix-build build the lib and one of its example programs with ghcjs.
At the moment, nix-build makes only the lib. Is it somehow possible to tell in the libx.nix or in the default.nix to also build one of the example-programs, say ex1? That is, to tell for the build process to cabal new-build ex1 and then install the result just like it installs the lib.
To use ghcjs, to build the ex1 that is targeted to ghcjs, it is possible to nix-shell --argstr "compiler" "ghcjs" and then cabal new-configure --ghcjs etc. (So, outside nix-shell, the nix-build -command is not doing all I'd like it do.)
Is it required to make a nix-files into the example-directory? Somehow this does not sound that appealing as the required modules are already given in libx.nix. That is, should I do something like in the answer to how to get cabal and nix work together?
Or is there a haskell package in github having similar structure that could work as an example?
Ideal solution would be that nix-build would build the lib and all its example programs. That would require the use of different building tools (ghc and ghcjs). Thus, maybe the question is, how to make a nix-setup for a multipackage cabal-project where individual packages need different environments including the compilation tools. On ideal world, the default nix-build would build all, and user could parameterize the nix-build to build the chosen example or examples etc.
It appears that the discussions in cabal issue 4646 and in cabal2nix issue 286 are possibly related.
