with builtins; let fold = op: nul: list: if list == [ ] then nul else op (head list) (fold op nul (tail list)); concat = fold (x: y: x + y) ""; asi = name: value: { inherit name value; }; list = [ (asi "a" "A") (asi "b" "B") ]; a = builtins.listToAttrs list; b = builtins.listToAttrs (list ++ list); r = builtins.listToAttrs [ (asi "result" [ a b ]) (asi "throw" (throw "this should not be thrown")) ]; x = builtins.listToAttrs [ (asi "foo" "bar") (asi "foo" "bla") ]; in concat (map (x: x.a) r.result) + x.foo