How to install a latest / unstable Haskell package executable in Nixos?

Question

I'm trying to get the latest version of ghcid installed.

I've installed ghcid via adding haskellPackages.ghcid in my nix config like so:

{ config, pkgs, ... }:

let
  unstable = import <unstable> {};
in
{
   environment.systemPackages = with pkgs; [
     haskellPackages.ghcid
   ];
}

---

I thought possibly it would be available as a specific package but I can't seem to find anything:

nix-env -v -qaP haskellPackages.ghcid

And

nix-env -v -qaP ghcid

Return ...matches no derivations

Answer 1

Surprisingly simple:

 unstable.haskellPackages.ghcid