$ nix-env -iA nixos.altcoins.mist
error: attribute 'mist' in selection path 'nixos.altcoins.mist' not found

$ git clone --depth 1 https://github.com/NixOS/nixpkgs.git ~/nixpkgs-unstable
$ nix-env -iA nixos.altcoins.mist -f ~/nixpkgs-unstable

error: the expression selected by the selection path 'nixos.altcoins.mist' should be a set but is a function