<?php
/**
 * A Maybe Monad class, encapsulates null checking
 */
class Maybe {

  private $value;

  public function __construct($value=null) {
    $this->value = $value;
  }

  public function isEmpty() {
    return is_null($this->value);
  }

  public function nonEmpty() {
    return !$this->isEmpty();
  }

  public function map($fn) {
    if ($this->isEmpty()) {
      return $this;
    } else {
      return new Maybe($fn($this->value));
    }
  }

  public function getOrElse($default) {
    if ($this->isEmpty()) {
      return $default;
    }
    return $this->value;
  }

}