sealed.php

<?php

sealed abstract class Maybe for Some, None {
  const None = new None();
  
  public static function Some(public readonly $val) {
    return new Some($val);
  }
}

class Some extends Maybe {
  protected function __construct(public readonly $value) {}
  
  public function bind(callable $c) {
    return $c($this->value);
  }
}

class None extends Maybe {
  public function bind(callable $c) { return $this; }  
}

function stuff(string $bla) {
  return $blah == '' ? Maybe::None : strlen($blah);
}

// vs

sealed abstract class Maybe for Some, None {
  protected static None $none;
  
  public function None() {
    return static::None ??= new None();
  }
  
  public static function Some(public readonly $val) {
    return new Some($val);
  }
}

function stuff(string $bla) {
  return $blah == '' ? Maybe::None() : strlen($blah);
}