Functional data structures experiments in php

functional-php-data.php

<?php

interface øList {
  function getHead();
  function getTail();
}

class øSimpleList implements øList {

  function __construct($head, øList $tail)
  {
    $this->requireType($head, $tail);
    $this->head = $head;
    $this->tail = $tail;
  }

  function getHead()
  {
    return $this->head;
  }

  function getTail()
  {
    return $this->tail;
  }

  private function requireType($x, øList $xs)
  {
    if(null == $xs->getHead())
      return true;

    $class = get_class($xs->getHead());
    if(! $x instanceOf $class )
      throw new Exception('Type Error');
  }

} function øList($head, øList $tail) {return new øSimpleList($head, $tail);}

class øNullList implements øList {
  function getHead() {return null;}
  function getTail() {return null;}
} function øNullList() {return new øNullList();}

class øInt { 
  function __construct($value)
  { 
    if(!is_int($value))
      throw new Exception('Type Error');
    $this->value = $value;
  } 
} function øInt ($value) { return new øInt($value);}

function toList(array $a)
{
  $list = øNullList();
  foreach($a as $n)
  {
    $list = øList(øInt(2),$list);
  }
  return $list;
}

var_dump(toList(range(1,10)));

exit;