source: liblaziness/test/fib.h @ 24

#ifndef __FIB_H__
#define __FIB_H__
#include "../list.h"
#include "../lazy_op.h"

class FibBase : List<Int>
{
        public:
                virtual ~FibBase() { }

                virtual Lazy<Int> getHead() { return head; }
                virtual LazyList<Int> getTail() { return tail; }
                virtual bool isEmpty() { return false; }

                friend LazyList<Int> mkFib();
                friend R<FibBase> Ref::mk<FibBase>();
        private:
                FibBase() : List<Int>(), head(suspend((Int)0L)), tail() { }
                Lazy<Int> head;
                LazyList<Int> tail;
};

LazyList<Int> mkFib()
{
        static auto init = []
        {
                R<FibBase> fib  = Ref::mk<FibBase>();
                LazyList<Int> l = suspendP<List<Int>, FibBase>(fib);
                fib->tail       = zipWith(LazyOp<Int>::add, l, suspend((Int)1L) <<= l);
                return l;
        };
        static LazyList<Int> l = init();
        return l;
}


typedef R<FibBase> Fib;

#endif