{ callPackage, from-elisp }: {
  org-tangle = block-predicate: text: let
    blocks = (callPackage from-elisp { }).parseOrgModeBabel text;
    block-to-str = block:
      if block-predicate { inherit (block) language flags; } then
        block.body
      else
        "";
  in
    builtins.concatStringsSep "\n" (map block-to-str blocks); 
}