defgaurd is a macro and as such it expects to receive Elixir AST as its arguments and it will return Elixir AST as its result. So the type of defguard is really something similar to:
@spec is_pos_integer(Macro.t) :: Macro.t
Which, as you are probably already saying, isn’t very illuminating and partially why adding specs to a defguard isn’t particularly useful.
I typically just add a @doc block to defguarda to document the underlying semantics.
