[Haskell-cafe] GHCJS Bad first impression

David Johnson djohnson.m at gmail.com
Tue Nov 1 23:47:03 UTC 2016

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 =
                   version = "";
                                                   sha256 = "... some hash
       isLibrary = false;
                                         isExecutable = false;

 description = "DOM library using JSFFI and GHCJS";

       license = stdenv.lib.licenses.mit;
                                 hydraPlatforms =
 }) {};


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)?


On Tue, Nov 1, 2016 at 2:43 AM, Peter Simons <simons at 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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