# This defines a function taking `pkgs` as parameter, and uses
# `nixpkgs` by default if no argument is passed to it.
{ pkgs ? import <nixpkgs> {} }:
# This avoids typing `pkgs.` before each package name.
with pkgs;
# Defines a shell.
mkShell {
  # Sets the build inputs, i.e. what will be available in our
  # local environment.
  buildInputs = [ haskell.compiler.ghc863 zlib ];
}