Default environments for various languages under nix and nixpkgs

To open an environment with R available, use nix-shell with the appropriate shell.nix.LANG:

$ nix-shell shell.nix.R

I assume copying the shell.nix into each project directory will be the best workflow:

$ mkdir new_project && cd new_project
$ cp <prefix>/shell.nix.R shell.nix
$ nix-shell

A custom set of nixpkgs can be specified. For example, if NIX_PATH is set, `nixpkgs=...:custom-nixpkgs=...', then:

$ nix-shell shell.nix.R --arg nixpkgs '<custom-nixpkgs>'

Can drop immeidately into a command/shell of choice. For example,

$ nix-shell shell.nix.R --arg nixpkgs '<custom-nixpkgs>' --command zsh
$ nix-shell shell.nix.R --arg nixpkgs '<custom-nixpkgs>' --command R