“Styx: there is no looking back.”

Styx is a convenient wrapper around cabal2nix, nix-shell and cabal new-<command>.

• get nix: https://nixos.org/nix/
• install the prerequisites (cabal2nix and cabal)

  nix-env -f "<nixpkgs>" -iA haskellPackages.cabal2nix
  nix-env -f "<nixpkgs>" -iA haskellPackages.cabal-install
      

• install styx:

  nix-env -f "<nixpkgs>" -iA haskellPackages.styx
      

In a directory of your choice, create a styx.yaml file like so:

# List the packages that you edit locally and want compiled "all the time", by cabal:
local-packages:
  my-main-package: # package name
    location: main # location on your disk (directory)
  my-local-dep:    # package name
    location: dep  # location on your disk (directory)

# Optionally, list patched or cutting edge packages that you depend on.
# These will be compiled only once, by nix.
source-deps:
  mtl:
    location: https://github.com/mrawesome/awsm-patched-version-of-mtl.git
    # revision: cc9a31305421f6bc72cc1f107f1270bd178c78a1 # optional

# Optionally, add other haskell nix packages to depend on.
# Normally this is not necessary, because nix will track the dependencies on its own.
# Thus this section is mostly useful for throw-away projects which do not have a well-formed cabal file.
nix-deps:
    - criterion
    - gasp
    - lens
    - statistics

# In case you depend on other non-haskell tools or libs.
non-haskell-deps:
    - z3

# Optionally, one can ask for a specific version of nixpkgs:
nixpkgs:
  commit: 8ef3eaeb4e531929ec29a880cb4c67f790e5eb70
  sha256: 4d2fae900d2d99ea294f4f412289af77152ac21d7b2e9ff23581ef11ea00831f
  # or like this: url: https://github.com/NixOS/nixpkgs-channels/archive/nixos-14.12.tar.gz

# Optionally, one can ask for a specific version of ghc, as known by nixpkgs
default-compiler: ghc801

Then, the command

styx configure

will create one nix file for each external package, a suitable shell.nix, and a cabal.project file.

You can then access the sandbox, inside the nix shell, like so:

nix-shell .styx/shell.nix --run "cabal ..."

Styx provides a couple of convenience commands:

$ styx build # runs cabal new-build in the shell
$ styx repl # runs cabal new-repl in the shell
$ styx exec <cmd> # runs cabal exec in the sandbox
$ styx cabal <cmd> # runs cabal <cmd> in the sandbox