Implement partial function application

[thekid]

Examples

This code:

class Person {
publicfunction__construct(publicint$id, publicstring$name) { }
}
// Returns an array of three Handle instances$handles= array_map(fn($_) => newHandle($_), [STDIN, STDOUT, STDERR]);
// Use time() function in production, specialized testing clock for unit tests$time= $test ? newTestingClock() : 'time';
// Executes HTTP request, then returns a function to read the given input stream$in= $http->get()->in();
$read= fn() => Streams::readAll($in);
// Creates instances from database records and writes them to the console
Sequence::of($conn->query('select * from person'))
->map(fn($_) => newPerson(...$_))
->each(fn($_) => Console::writeLine('> ', $_))
;

...can be rewritten to:

class Person {
publicfunction__construct(publicint$id, publicstring$name) { }
publicstaticfunctionfrom($record) { returnnewself(...$record); }
}
// Returns an array of three Handle instances$handles= array_map(newHandle(?), [STDIN, STDOUT, STDERR]);
// Use time() function in production, specialized testing clock for unit tests$time= $test ? newTestingClock() : time(...);
// Executes HTTP request, then returns a function to read the given input stream$read= Streams::readAll($http->get()->in(), ...);
// Creates instances from database records and writes them to the console
Sequence::of($conn->query('select * from person'))
->map(Person::from(?))
->each(Console::writeLine('> ', ?))
;

See also

• https://wiki.php.net/rfc/partial_function_application
• [RFC] Partial Function Application php/php-src#6898
• https://github.com/tc39/proposal-partial-application
• https://babeljs.io/docs/en/babel-plugin-proposal-partial-application

Depends on xp-framework/ast#26

[thekid]

If we allowed unpacking of placeholders via ...?, we could further simplify the sequence example:

class Person {
publicfunction__construct(publicint$id, publicstring$name) { }
}
// Creates instances from database records and writes them to the console
Sequence::of($conn->query('select * from person'))
->map(new Person(...?))
->each(Console::writeLine('> ', ?))
;

[thekid]

When we pass around objects as parameters, the placeholder would have to be able to replace the object in something like the following:

$filtered= Sequence::of(...)->filter(fn($user) => $user->isActive());
$filtered= Sequence::of(...)->filter(?->isActive());

Hrm...

[thekid]

RFC was declined, closing

[faizanakram99]

RFC was declined, closing

it would have been still a nice feature