Hi Peti,

Thanks for chiming in on this, was not aware cabal2nix's ghcjs functionality. This is great. There are some packages in haskellPackages (ghcjs-dom-jsffi) that are really only meant to be used with ghcjs. In this case would it be appropriate to somehow detect this, and use the "--compiler-ghcjs" flag during generation? Or is it better for us to resort to overriding all ghcjs specific packages on hackage in "pkgs/development/haskell-modules/configuration-ghcjs.nix" ? 

The derivation below is pretty much useless for anyone using GHC (not a library nor executable, 0 deps specified). I imagine as GHCJS continues to grow, and hackage contains more 'ghcjs-only' packages, it will become onerous to continally override in configuration-ghcjs.nix (ghcjs-dom is also a good example of needing to do this).

```
"ghcjs-dom-jsffi" = callPackage ({ mkDerivation }:                                           mkDerivation {                                                                                                    pname = "ghcjs-dom-jsffi";                                                                            version = "0.5.0.2";                                                                                        sha256 = "... some hash ...";                                         
       isLibrary = false;                                                                                            isExecutable = false;                                                                                      description = "DOM library using JSFFI and GHCJS";                           
       license = stdenv.lib.licenses.mit;                                                                    hydraPlatforms = stdenv.lib.platforms.none;                                                }) {}; 

```  

Peti, is there a way we could generate two derivations (w/ and w/o the --ghcjs flag) and conditionally select the one we want based on the compiler (meaning ghcjs vs. latest ghc)? 

Regards,

David

On Tue, Nov 1, 2016 at 2:43 AM, Peter Simons <simons@nospf.cryp.to> wrote:
Hi David,

 > cabal2nix doesn't generate nix expressions that are sensitive to ghcjs.

the expressions in Nixpkgs target GHC 8.0.x, not GHCJS. If you want
cabal2nix to generate expressions for GHCJS instead, then you'll just
have to run it with the flag "--compiler=ghcjs". Builds generated by the
Nix function haskell.packages.ghcjs.callHackage do this automatically.

Best regards,
Peter

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