yammat: build for all available ghc versions

yammat.nix

@@ -2,8 +2,16 @@
 }:
 with pkgs;
 let
-  yammat = haskellPackages.callPackage <yammat> {};
-  jobs = {
-    inherit yammat;
-  };
-in builtins.mapAttrs (name: lib.hydraJob) jobs
+  yammat = haskellPackages:
+    haskellPackages.callPackage <yammat> {};
+  ghcVersions =
+    builtins.filter (p:
+      p == "ghcHEAD" || builtins.match "ghc[[:digit:]]+" p != null
+    ) (builtins.attrNames haskell.packages);
+in
+
+builtins.listToAttrs
+  (map (ghcVersion: {
+    name = "yammat-${ghcVersion}";
+    value = lib.hydraJob (yammat (builtins.getAttr ghcVersion haskell.packages));
+  }) ghcVersions)