[dub_gui]

To clarify, the type-checker does not modify compilation to the beam at all. Instead, it takes into account the predicted runtime checks to inject more static types into its analysis.

For instance, without even introducing annotations, if a function head has a guard `is_boolean(x)`, using the + operator on x within that function would lead to a type error.

[throwawaymaths]

exactly. The potential performance regression of guards is exactly why the elixir typechecker doesn't insert them. I guess I hadn't made that point clear in my comment. IIRC The elixir guides talks about excessive typechecking being a code smell.