Why Typing Erlang is Hard: Standard Erlang

Re:Why Typing Erlang is Hard: Standard Erlang by dnautics on Friday November 06, 2020 @11:09AM (#25008650)

Yeah, I mean that it will properly identify that the only time you can do that is when you have an empty list. The final spec will be (in elixir syntax):

    (nonempty_list, number -> number) | ([], any -> any)

It should also be able to correctly infer that the count/1 function must be

    (nonempty_list -> pos_integer) | ([] -> 0)

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Re:Why Typing Erlang is Hard: Standard Erlang by Joker_vD on Friday November 06, 2020 @11:33AM (#25008859)

I am using an old version of erlang, so typer infers the following types:

    -spec count([any()],_) -> any().
    -spec count([any(),...]) -> any().

If I unexport count/2, it infers

    -spec count([any(),...]) -> non_neg_integer().
    -spec count([any()],non_neg_integer()) -> non_neg_integer().

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Re:Why Typing Erlang is Hard: Standard Erlang by dnautics on Friday November 06, 2020 @11:57AM (#25009073)

I did say "should be able to" without regard to any of the existing type inference engines =D I'll be sure to make this as explicit test in Mavis Inference, which is the one I'm working on. https://github.com/ityonemo/mavis_inference/issues/47

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