Simplest possible Haskell flake

[sternenseemann]

You are importing <nixpkgs> (which does a lookup in NIX_PATH and is completely independent from the nixpkgs variable in scope) instead of plain nixpkgs.

There seems to have been a recent thread on the topic of legacyPackages/import:

Using nixpkgs.legacyPackages.${system} vs import

I experimented the following flake.nix and both cowsay and ponysay work well with direnv. { description = "cowsay ponysay"; inputs = { nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable"; stable.url = "github:NixOS/nixpkgs/nixos-21.11"; flake-utils.url = "github:numtide/flake-utils"; }; }; outputs = { self, nixpkgs, stable, flake-utils, ... }: flake-utils.lib.eachDefaultSystem (system: let pkgs = nixpkgs.legacyPackages.${system}; stablepkgs = import …