New EEP draft: Pinning operator ^ in patterns

Nicolas Martyanoff khaelin@REDACTED
Thu Jan 14 15:32:17 CET 2021

On 2021-01-14 14:13, Richard Carlsson wrote:
> The way I planned it is:
>   1. Even from the start, pinning will always be allowed, without requiring
> any flag to opt in. This does not tell you about existing uses of
> already-bound variables, but you can start using pinning right away for
> readability and for avoiding bugs when refactoring. The compiler will
> always tell you if a pinned variable doesn't exist, so you don't
> accidentally accept any value in that position.
>   2. You can enable warnings at your own pace in order to start cleaning up
> your code.
>   3. In a following major release, the warnings will be on by default, but
> you can disable them to compile old code.
>   4. In a distant future, it might become an error to not use ^ to mark
> already-bound variables.

After reading this thread, I must say this proposal makes me uneasy. One of
the things I always liked with Erlang is the simplicity and clarity of its
syntax. Matching variables by name is perfectly readable to me, and I never
had any problem of the sort refactoring code. Adding a new operator adds 
noise and transforms something simple (using the same name to refer to the
same value) into something cryptic.

The fact that you envision a future where not using the operator would signal 
an error is even more worrisome. I have nothing against improving the core
parts of the language (maps were a life changer for example), but this kind of
change feels really foreign to the simplicity of the Erlang syntax.

And at the risk of sounding too harsh, I would add that while I do not mind the
existence of Elixir (quite the opposite, it brought a lot of fresh air to the
entire BEAM ecosystem), I would really like Erlang to remain Erlang; in that 
spirit, I see a new operator to "annotate" a perfectly clear and working 
syntax as useless.


Nicolas Martyanoff

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