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Date: Sun, 25 Apr 2021 18:34:05 +0200
Message-ID: <CAJpLVh3DaQ1qgddHuccTr=4DQp03rEcJGavx1J-7nseVnBFUcw@mail.gmail.com>
To: Larry Garfield <larry@garfieldtech.com>
Cc: php internals <internals@lists.php.net>
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Subject: Re: [PHP-DEV] [RFC][Draft] Sealed Classes
From: olleharstedt@gmail.com (=?UTF-8?Q?Olle_H=C3=A4rstedt?=)

2021-04-25 18:27 GMT+02:00, Larry Garfield <larry@garfieldtech.com>:
> On Sun, Apr 25, 2021, at 2:04 AM, Olle H=C3=A4rstedt wrote:
>> > A total function is a function that is defined over the entire domain =
of
>> > its
>> > inputs.  For example, addition is a total function over integers,
>> > because
>> > for every possible pair of integers you pass to it there is a logical
>> > return
>> > value.  However, square root is not a total function over integers
>> > because
>> > there are some integers you pass it for which there is not
>> > representable
>> > return value.  (Negative numbers, unless you get into imaginary number=
s
>> > which PHP doesn't support.)  In those cases, you have to throw an
>> > exception
>> > or return an error code or similar.
>>
>> Maybe nitpicking, but PHP-land shouldn't make up their own
>> definitions: "A total function is a function that is defined for all
>> possible values of its input. That is, it terminates and returns a
>> value."
>> https://softwareengineering.stackexchange.com/questions/334874/in-the-co=
ntext-of-functional-programming-what-are-total-functions-and-partia
>>
>> Which means a total function is guaranteed to not have any errors,
>> like exceptions or division by zero. Compare with languages F* or Koka
>> which support this notation.
>
> That... is literally what I said.  There was no making up definitions.  I
> was using the actual mathematical definition.  PHP is quite capable of
> having total functions, they're a good thing, and we should try to encour=
age
> them where feasible.

What's the point of encouraging total functions if you can't express
the totality in the type system?

Olle