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Date: Sat, 27 Mar 2021 16:14:45 +0100
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To: Rowan Tommins <rowan.collins@gmail.com>
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Subject: Re: [PHP-DEV] Making "match" catch exceptions
From: olleharstedt@gmail.com (=?UTF-8?Q?Olle_H=C3=A4rstedt?=)

2021-03-27 15:30 GMT+01:00, Rowan Tommins <rowan.collins@gmail.com>:
> On 26/03/2021 22:58, Olle H=C3=A4rstedt wrote:
>> You can't catch the value of $temp in the match-case?
>>
>>      $foo =3D $bar + match (doSomething()) {
>>        $temp =3D> $temp,
>>        exception SomeException =3D> 0
>>      };
>
>
> $temp doesn't have an outside value, it was an inline assignment to
> capture the value of doSomething(); essentially, I wanted this, but
> without executing doSomething() twice:
>
> $foo =3D $bar + match (doSomething()) {
>        default =3D> doSomething(),
>        exception SomeException =3D> 0
> };

Yeah, I got it. Maybe I didn't read enough about the match-expression
implementation in PHP, but in OCaml it's possible to capture whatever
value the match evaluated to, like:

    let number_as_string =3D match number with
    | 1 -> "one"
    | v -> "number is " ^ string_of_int v

("^" is string concatenation.)

The point of using a variable name like "v" (could be anything)
instead of "default" is that like in your example, you don't have to
execute the method twice. You can also add guard clauses, like "v when
v > 10 -> ...". If you don't plan to use the value, you can use
underscore, "_", which I guess would be the corresponding
functionality to "default" in the PHP implementation.

Olle