ocamlPackages.ocaml_mysql: set pname instead of name

pkgs/development/ocaml-modules/mysql/default.nix

@@ -12,16 +12,13 @@
 # qualche cambiamento negli header .h
 # TODO: compilazione di moduli dipendenti da zip, ssl, tcl, gtk, gtk2
 
-let
+stdenv.mkDerivation (finalAttrs: {
+  name = "ocaml${ocaml.version}-${finalAttrs.pname}-${finalAttrs.version}";
   pname = "ocaml-mysql";
-in
-
-stdenv.mkDerivation rec {
-  name = "${pname}-${version}";
   version = "1.2.1";
 
   src = fetchurl {
-    url = "http://ygrek.org.ua/p/release/ocaml-mysql/${name}.tar.gz";
+    url = "http://ygrek.org.ua/p/release/ocaml-mysql/ocaml-mysql-${finalAttrs.version}.tar.gz";
     sha256 = "06mb2bq7v37wn0lza61917zqgb4bsg1xxb73myjyn88p6khl6yl2";
   };
 
@@ -54,4 +51,4 @@ stdenv.mkDerivation rec {
     license = lib.licenses.lgpl21Plus;
     maintainers = [ lib.maintainers.roconnor ];
   };
-}
+})