Use typespec in the correct way

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The output you got from dialyzer uses erlang syntax, so you need to know, how to translate it to elixir syntax, to actually make sense from it.

  • Erlang does not have nested modules, so elixir modules are prepended by Elixir. and then used as modulename completely.
  • Erlang does separate module and function name by a colon, not a dot.
  • Atoms are just written as they are, but for some special cases the are enclosed in singlequotes. Dialyzer output does use singlewquotes unconditionally.
  • Typenames in erlang have to use parens.

Knowing this, we can read the output line (which was Invalid type specification for function 'Elixir.Pdf.Inspector':validate/1. The success typing is (binary()) -> {'error'} | {'ok'}) as Invalid type specification for function Pdf.Inspector.validate/1. The success typing is (String.t) -> {:error} | {:ok}.

So dialyzer complains, that you are returning either {:ok} or {:error}, while you are specifying to return ONLY {:atom}. So dialyzer does tell you which was the correct type of your function.

If you want to specify any atom you have to use {atom} instead of {:atom}.

Additionally to your question which is related to dialyzer, I do see some problems as well, which I want to address here only in short:

  • Instead of using an unary tuple, in most cases it would be better to use the value directly
  • gs will probably always fail, for a further axplanation why, see your other thread about System.cmd/2 (https://elixirforum.com/t/double-quotes-in-string/1489?u=nobbz)
  • gs does not only exit with 0 or 1 but with any integer, 0 meaning “no error” and any other value signals an error. Which value is for what kind of error is written somewhere in the gs manual.
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