Re: Re: [RFC] Arrow functions / short closures

On Thu, March 14, 2019 10:41 AM Nikita Popov <nikita.ppv@gmail.com> wrote: > On Wed, Mar 13, 2019 at 4:56 PM Nikita Popov <nikita.ppv@gmail.com> wrote: > > > Hi internals, > > > > Motivated by the recent list comprehensions RFC, I think it's time we took > > another look at short closures: > > > > https://wiki.php.net/rfc/arrow_functions_v2 > > As a small update, I've implemented a proof of concept that uses the ($x) > ==> $x * $multiplier syntax (or $x ==> $x * $multiplier for short) in > https://github.com/php/php-src/pull/3945. As mentioned in the > RFC, this > requires scanahead in the lexer. > > This syntax is in principle still on the table, though personally I prefer > fn($x, $y) => $x * $y over ($x, $y) ==> $x * $y. The main redeeming quality > of ==> is that it supports the paren-less variant $x ==> $x. Taking into > account the lexer hackery it requires (and which will also be required in > any 3rd party tooling), this would not be my preferred choice. > I agree that the nicest thing about this syntax is the ability to save an additional 3 characters of boilerplate for the common use case of single-parameter arrow functions. However, I'm also not a fan of adding complex code hacks to make the syntax work. One alternative that doesn't seem to have had much discussion on list is the \($x) => $x * $y lambda syntax. This would also allow parentheses to be omitted for single parameters, making it just as terse as the ==> syntax without the need for any lexer hackery. Here's how the examples from the RFC would look: ```php function array_values_from_keys($arr, $keys) { return array_map(\$x => $arr[$x], $keys); } $extended = \$c => $callable($factory($c), $c); $this->existingSchemaPaths = array_filter($paths, \$v => in_array($v, $names)); function complement(callable $f) { return \(...$args) => !$f(...$args); } $result = Collection::from([1, 2]) ->map(\$v => $v * 2) ->reduce(\($tmp, $v) => $tmp + $v, 0); ``` One argument against this shorter syntax is that it wouldn't be as easy to google as fn. However, long term I think everyone would still get used to it, and I'm personally willing to add an answer to the top Stack Overflow search result for "php backslash keyword". The backslash syntax has precedent from Haskell, and also wouldn't introduce any BC break (who knows how many private codebases might already have functions named fn).