I have the following `shell.nix` (to setup my development environment, no NixOS):

```
with import <nixpkgs> {};

stdenv.mkDerivation {
    name = "my-shiny-project";
    buildInputs = [
        jq
        nodejs-6_x
        #postgis {version="2.3.1";}
        #postgis ("2.3.1")
        #postgis "2.3.1"
        postgresql96
        zsh
    ];
    shellHook = ''
        export SHELL=zsh
        export PATH="$PWD/node_modules/.bin/:$PATH"
    '';
}

```

PostGIS expects a version parameter. I'm not sure how to pass that parameter along. Whether I use `postgis{version="2.3.1";}`, `postgis("2.3.1")` or `postgis "2.3.1"`, I receive the following error:

> 
> error: cannot coerce a set to a string, at /nix/store/0rj9y7gvzzahp93cvdmrwc2v2aznh61p-nixpkgs-18.03pre118061.69607d7662/nixpkgs/pkgs/stdenv/generic/make-derivation.nix:98:11
> 
> 
> 

In the [Nameless and single parameter section of functions and imports Nix pill](https://nixos.org/nixos/nix-pills/functions-and-imports.html#idm140737316567856), I see the syntax for calling a function is simply `NAME PARAM`.

What do I have to add to `buildInputs` to get PostGIS installed for that specific version of PostgreSQL?