<?php

declare(strict_types=1);

use Fp4\PHP\Option as O;

use function Fp4\PHP\Combinator\pipe;

/** @var string|int */
$stringOrNumber = 'str';

// current type is: Option<Bindable<object{a:int|string}>>
// should be is: Option<Bindable<object{a:string}>>
$_ = pipe(
    O\bindable(),
    O\let(a: fn() => $stringOrNumber),
    O\filter(fn($i) => is_string($i->a)),
);