[Nix-dev] nix-shell for a custom haskell library

[Peter Simons]

Hi Dmitry,

 >> The "env" attribute of engine-io (which is what nix-shell enters
 >> here) gives you an environment in which engine-io can be compiled.
 >
 > If I remember correctly, old `haskellPackages.mkDerivation` was
 > producing an environment with compiled sources and installed
 > libraries.

I'm not sure what you mean. Pre-Haskell-NG packages had no support for
nix-shell at all, and the behavior in Haskell NG has never been different
from what it is now. mkDerivation builds and installs the library, of
course, but the while point of nix-shell is that the code which does this
is not executed automatically so that you can run your own commands
instead.


 > How to configure `shell.nix` to get `cabal configure && cabal build`
 > done after entering the nix-shell?

nix-shell --command "cabal configure && cabal build".


 > What was the reason to move this step out of nix-shell routine?

No such code ever existed in the nix-shell environment for Haskell
packages.

Best regards,
Peter