gradualizer

-module(erlang).

%% This module contains specs to replace incorrect or inexact specs in OTP.

%% The commented-out specs are the original specs from OTP 21 (erts-10.2.4) with
%% type variebles unfolded if they occur only once in the spec.

%% -spec hd([term(), ...]) -> term().
-spec hd([A, ...]) -> A.

%% -spec min(term(), term()) -> term().
%% -spec max(term(), term()) -> term().
-spec max(A, B) -> A | B.
-spec min(A, B) -> A | B.

%% -spec tl([term(), ...]) -> [term()].
-spec tl([A, ...]) -> [A].

-spec erlang:'--'(list(), list()) -> list().

%% The original spec is:
%%
%% -spec erlang:'++'(list(), term()) -> term().
%%
%% Now, this is funny:
%%
%%   > [] ++ b.
%%   b
%%   > [a] ++ b.
%%   [a|b]
%%   > [a, b] ++ c.
%%   [a,b|c]
%%   > [a|b] ++ c.
%%   ** exception error: bad argument
%%     in operator  ++/2
%%        called as [a|b] ++ c
%%   > [] ++ [a].
%%   [a]
%%   > [a,b] ++ [c].
%%   [a,b,c]
%%   > [a|b] ++ [c].
%%   ** exception error: bad argument
%%        in operator  ++/2
%%           called as [a|b] ++ [c]
%%
-spec erlang:'++'([], T)                                     -> T;
                 ([T1, ...], [T2])                           -> [T1 | T2, ...];
                 ([T1], [T2])                                -> [T1 | T2];
                 ([T1, ...], nonempty_improper_list(T2, T3)) -> nonempty_improper_list(T1 | T2, T3);
                 ([T1], nonempty_improper_list(T2, T3))      -> nonempty_improper_list(T1 | T2, T3);
                 ([T1, ...], T2)                             -> nonempty_improper_list(T1, T2).


%% Prior to OTP 24.1 the spec does not list `none' as valid `Args',
%% but the function accepts it and works properly.
-spec erlang:error(Reason, Args) -> no_return() when
      Reason :: term(),
      Args :: [term()] | none.

%% `erlang:error/3' was introduced in OTP 24, but it's spec is also fixed only since OTP 24.1.
-spec erlang:error(Reason, Args, Options) -> no_return() when
      Reason :: term(),
      Args :: [term()] | none,
      Options :: [Option],
      Option :: {'error_info', ErrorInfoMap},
      ErrorInfoMap :: #{'cause' => term(),
                        'module' => module(),
                        'function' => atom()}.