Why do type specs in OTP repeat parameter names?

Question

In type specs for the Erlang standard library, there are almost never any types in the spec until the when clause. For example, the spec for lists:member/2 is like this:

-spec member(Elem, List) -> boolean() when
      Elem :: T,
      List :: [T],
      T :: term().

instead of:

-spec member(Elem :: T, List :: [T]) -> boolean() when
      T :: term().

Is there a reason for this? Are these two styles equivalent from the dialyzer's point of view?

score 3 · Accepted Answer · answered May 31 '20 at 14:46

3

It is done that way because the documentation that is generated from the specs looks better if done like that.

answered May 31 '20 at 14:46

Lukas

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17

Thanks, Lukas. Are the two styles equivalent from the dialyzer's point of view? – Max Heiber May 31 '20 at 15:16
1

Yes, they should be. You made a typo in your example though, so in the question the specs are not the same. – Lukas May 31 '20 at 17:08

Why do type specs in OTP repeat parameter names?

1 Answers1