Timothy Emiola

@alpmestan just checking in - this is approved, so I assume a maintainer will merge it ?

Turning on --show-trace gives: ``` error: while evaluating the attribute 'buildInputs' of the derivation 'rokubanme-no-purojekuto-1.0.0' at /nix/store/ispccm8khhpmz10d8nf9mlnjd1mjlwpv-nixpkgs-18.09pre134915.0288f77c300/nixpkgs/pkgs/stdenv/generic/make-derivation.nix:148:11: while evaluating the attribute 'propagatedBuildInputs' of the derivation 'foldl-1.3.7' at /nix/store/ispccm8khhpmz10d8nf9mlnjd1mjlwpv-nixpkgs-18.09pre134915.0288f77c300/nixpkgs/pkgs/stdenv/generic/make-derivation.nix:148:11: while evaluating...

This points to the fact that there is an issue building optparse-applicative from the json file. > while evaluating the attribute > 'nativeBuildInputs' of the derivation > 'cabal2nix-optparse-applicative' at /nix/store/ispccm8khhpmz10d8nf9mlnjd1mjlwpv-nixpkgs-18.09pre134915.0288f$7c300/nixpkgs/pkgs/stdenv/generic/make-derivation.nix:148:11:...

During the implementation #35, it became clear that this problem affects the foldl package as well.

@fujimura, I'm happy to take a look at this it sounds like a very useful feature. If I send a PR with it, do you have time to review it?

Thank you for the quick response! I have just tried this out, and I get a different error, which I think may also be related to type family instances. ```haskell...

Thanks! I also had to an `AddSetCookies` instance for `Functor Application`, which works because servant-auth already provides an instance for `Application`. ```haskell -- Type instance for RawM for SetCookie API...