Install Cabal, GHC, or GHCJS with one Nix command

minimal_ghc_ghcjs_nix.sh

# install nix (5.5 mins)
curl https://nixos.org/nix/install | sh

# open a new shell to source nix
bash

# query available haskell compilers
nix-env -qaP -A nixpkgs.haskell.compiler [QUERY]

# install ghc (2.5 mins, cached binary)
nix-env -iA nixpkgs.haskell.compiler.ghc865

# ghc is now in your PATH
ghc --version

# query cabal install version
nix-env -qaP -A nixpkgs.haskellPackages.cabal-install

# install cabal install (0.5 mins, cached binary)
nix-env -iA nixpkgs.haskellPackages.cabal-install

# cabal is now in your PATH
cabal --version

# Install ghcjs (take one sleep, build from source, with `-j1`)
# https://github.com/NixOS/nixpkgs/blob/67e07308236bb7a9fa11f3b599838384db650ecb/pkgs/development/compilers/ghcjs-ng/default.nix#L96
# It will appear to hang at places like 'Preprocessing library for unix-2.7.2.2..'
# Use `ps -ef | grep nix` to check it is still doing work.
nix-env -iA nixpkgs.haskell.compiler.ghcjs

# ghcjc is now in your PATH
ghcjs --version

# cleanup disk space from unused nix stuff
nix-collect-garbage -d

# uninstall everything
sudo rm -rf /nix