CL and iterators - a newbie question

sirola_at_fisica.unige.it
Date: 05/23/04 

Date: Sun, 23 May 2004 18:36:51 GMT

Hello,
I'm learning lisp and, as an exercise, trying to implement iterators
with CL. I implemented a simple as follows, using a closure:

(defun sarray-iterator (v &key (start 0))
  (declare (type (simple-array double-float) v)
           (type fixnum start))
  (let ((next-position start))
    (declare (type fixnum next-position)
             (type double-float result))
    #'(lambda ()
        (let ((result 0d0))
          (setq result (aref v next-position))
          (incf next-position)
          result))))

I tried to profile it a bit using the following code:

(setf (symbol-function 'try2) (sarray-iterator
                               (make-array 500000
                                           :element-type 'double-float
                                           :initial-element 1.0d0)
                               :start 0))
(profile:profile try2)
(try2)
(profile:report-time)

the profiler (cmucl) reported

  Consed | Calls | Secs | Sec/Call | Bytes/C. | Name:
-----------------------------------------------------------------------
         16 | 1 | 0.000 | 0.00000 | 16 | TRY2

so it seems the iterator conses 16 bytes per call (2 double
floats?), am I right? Where does the cons happen? Is it possible to
write a non-consing iterator?
Thanks in advance,
e. 

-- 
Enrico Sirola

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