This is a WIP do not expect it to work yet, please. Also I intend to use it more for an integration approach nix-wise than to actually enhance the program sources themselves in any way. The latter which seemingly natural as it is just kind of a tutorial according to the original author's expressed intent.
cd ~/shorturls
cabal2nix . > shorturls.nix
default.nix and shell.nix are simple copies of the default templates given in the haskell section of nix' manual, noteworthy is setting compiler version string to "ghc7102" according to WJWH/shorturls/stack.yaml. Consequently nixpkgs=.../nixos-17.09.tar.gz is chosen as the compiler version fixed seems available just there.
The first build (nix-build -I nixpkgs=https://github.com/NixOS/nixpkgs-channels/archive/nixos-17.09.tar.gz) attempt triggered a package missing error, added transformers to cabal file plus repeated cabal2nix call above to reflect dependencies change. Also in subsequent builds a symbol undefined error (<>) was thrown, added the import to both src/Example.hs and test/Spec.hs.
nix-shell -p which nano git haskellPackages.ghc haskellPackages.cabal-install cabal2nix redis -I nixpkgs=https://github.com/NixOS/nixpkgs-channels/archive/nixos-17.09.tar.gz
redis-server &
nix-build -I nixpkgs=https://github.com/NixOS/nixpkgs-channels/archive/nixos-17.09.tar.gz
integrate manual work listed above for local building to haskell.yml as a first step.