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Edit summary for version 12 :

Version 11

Version 12

Idiom #3 Create a procedure

Like a function which doesn't return any value, thus has only side effects (e.g. Print to standard output)

Idiom #3 Create a procedure

Like a function which doesn't return any value, thus has only side effects (e.g. Print to standard output)

Code
-spec procedure() -> _.
procedure() -> io:format("#YOLO!~n").
Comments bubble
There is no way to avoid returning a value here. This function returns ok. But you can add -spec to say that you should not care about the result.