default.nix: allow passing compiler argstr

Author: sorki

default.nix

@@ -1,4 +1,5 @@
 { pkgs ? import <nixpkgs> {}
+, compiler ? null
 }:
 let
   overlay = import ./overlay.nix pkgs pkgs.haskell.lib;
@@ -9,8 +10,13 @@ let
       then pkgs.lib.composeExtensions orig.overrides overlay
       else overlay;
   };
-  haskellPackages =
-    pkgs.haskellPackages.override overrideHaskellPackages;
+
+  packageSet =
+    if compiler == null
+    then pkgs.haskellPackages
+    else pkgs.haskell.packages.${compiler};
+
+  haskellPackages = packageSet.override overrideHaskellPackages;
 in {
   inherit (haskellPackages) hnix-store-core hnix-store-remote;
   inherit haskellPackages;