you forgot the !. Without it those functions return an ok-tuple, with they raise.

ye it tried to move the decode above the random actually but then got:

** (ArgumentError) errors were found at the given arguments:

  * 1st argument: not an iodata term

    :erlang.iolist_to_binary(%File.Stream{line_or_bytes: :line, modes: [:raw, :read_ahead, :binary], path: "names.json", raw: true})

If you have a huge JSON file then you may consider using jaxon library instead.

Take a look at example from it’s readme file:

"large_file.json"
|> File.stream!()
|> Jaxon.Stream.from_enumerable()
|> Jaxon.Stream.query([:root, "users", :all, "metadata"])
|> Stream.map(&(&1["username"],",",&1["email"],"\n"))
|> Stream.into(File.stream!("large_file.csv"))
|> Stream.run()