[Proposal] range pattern matching in case without when

[Igor Silva]

Current behavior

case ?a do

  x when x in ?a..?z -> # code

  x when x in ?A..?Z -> # code

  _ -> # code

end

Desired behavior

case ?a do

  ?a..?z -> # code

  ?A..?Z -> # code

  _ -> # code

end

#GoiásouVilaNova

[Amos King]

Would this match on an element in a range and on an equivalent range? ?a or ?a..?z would both match with ?a..?z

The proposed code looks nice and I thought was simpler at first. Considering it further made me think of the situation above. I want the explicitness of the current behavior to reduce the ambiguity.

Amos King

CEO

Binary Noggin

On Mar 13, 2021, at 06:26, Igor Silva <computador...@gmail.com> wrote:

Current behavior

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[José Valim]

Thanks for the proposal,

However, ?a..?z in a pattern should match on a range from ?a..?z. Similarly, x..y can be used to match on any range and extract its values.

Those are all valid and correct today, and introducing this proposal would break said semantics.

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[eksperimental]

You can covert the case
case ?a do
x when x in ?a..?z -> :lower_case
x when x in ?A..?Z -> :upper_case
_ -> :unknown
end


into a cond:

cond do
?a in ?a..?z -> :lower_case
?a in ?A..?Z -> :upper_case
true -> :unknown
end

[Igor Silva]

I understand, how about it?

case ?a do

  in ?a..?z -> # code

  in ?A..?Z -> # code

  _ -> # code

end

Goiás ou Vila Nova?

[Ben Wilson]

I think eksperimental was dead on when he said what you really want is `cond`.

```

cond do

val in ?a..?z

val in ?A..?Z

```

Changing `case` to have an implicit `where` in certain special cases is going to make it behave inconsistently compared to other places that take patterns. Optimizing the characters for this specific case isn't worth the implicit magic ImHO.

[Wiebe-Marten Wijnja]

As addendum to this:

`cond` is often treated as if it were slower than `case`, and I've seen people try to rewrite readable `cond`-clauses to harder-to-read `case`-clauses to reap extra performance benefits.
(I'll admit: In the past I've been guilty of doing this as well.)

Benchmarking will however show you that in many cases this does not matter.
The BEAM compiler is clever enough to optimize repeated conditionals also outside `case`-clauses.

~Marten/Qqwy

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