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This page is part of the web mail archives of SRFI 41 from before July 7th, 2015. The new archives for SRFI 41 contain all messages, not just those from before July 7th, 2015.

stream-car and stream-cdr can be speeded up by writing stream-cons as follows:
(define-syntax stream-cons
    (syntax-rules ()
      ((stream-cons obj strm)
        (stream-eager (make-stream-pare (stream-delay obj) (stream-lazy strm))))))
Immediate construction of the stream-pare does not consume more memory than the preparation of a promise, saves two cycles in procedure stream-force and does not force anything that should not yet be forced. I checked this with the unit-test. In my own streams-library, the equivalent of the above stream-cons passes all leak-tests (even the times3 test in a Scheme implementation (not to be mentioned here) that is rather susceptible to leaks in procedure stream-force)
Jos Koot

((((lambda(x)((((((x x)x)x)x)x)x))
   (lambda(x)(lambda(y)(x(x y)))))
  (lambda(x)(write x)x))