diff --git a/psDeriver.nix b/psDeriver.nix
index b830b26..80d655a 100644
--- a/psDeriver.nix
+++ b/psDeriver.nix
@@ -2,6 +2,8 @@
 #
 # nodejs?: node derivation to use for running executables
 #
+# purescript?: purescript derivation to use for compilation
+#
 # deps:
 # {
 #   name
@@ -28,12 +30,13 @@
     
 
 { pkgs
+, purescript ? pkgs.purescript
 , nodejs ? pkgs.nodejs
 , deps
 , out }:
-with pkgs; with builtins;
+with builtins;
 let inputs =
-      map (d: stdenv.mkDerivation {
+      map (d: pkgs.stdenv.mkDerivation {
           name = d.name;
           version = d.version;
           src = d.src or fetchGit {
@@ -43,7 +46,7 @@ let inputs =
           installPhase = ''cp -r "$src" "$out"'';
         })
         deps;
-in stdenv.mkDerivation {
+in pkgs.stdenv.mkDerivation {
   pname = out.name;
   version = out.version;
   src = out.src;
diff --git a/readme.md b/readme.md
index 89d00fe..de265d1 100644
--- a/readme.md
+++ b/readme.md
@@ -12,7 +12,10 @@ Import `psDeriver.nix` and pass the following arguments:
 The usual nixpkgs
 
 ### `nodejs` (optional)
-Nodejs derivation to use for running executables. If not specified then `pkgs.nodejs` will be used.
+Nodejs derivation to use for running executables. If not specified then `pkgs.nodejs` will be used. Will not be used if no executable is specified.
+
+### `purescript` (optional)
+Purescript derivation to use for compilation. If not specified then `pkgs.purescript` will be used.
 
 ### `deps`
 A list of dependencies in one of the following formats: