[racket] Y-combinator perfomance

If I understand you correctly, it is possible to see such an optimization in Racket? It would be awesome to use this style to control the loops.

28.06.10, 23:47, "Matthias Felleisen" <matthias at ccs.neu.edu>:

> 
>  I pointed out Jinx's paper to Matthew last week.
>  
>  Not surprisingly, reality and theory never match with the MIT Scheme  
>  compiler.
>  
>  
>  On Jun 28, 2010, at 3:04 PM, Joe Marshall wrote:
>  
>  > On Fri, Jun 25, 2010 at 11:50 AM, Matthew Flatt   
>  > wrote:
>  >>
>  >> Compilers can't easily see through a Y combinator, and a factor of  
>  >> 8 or
>  >> so difference is probably typical for Lisp compilers. (I tried Ikarus
>  >> and Gambit to double check, and performance was about the same as  
>  >> with
>  >> Racket.)
>  >
>  > See
>  > @INPROCEEDINGS{Juan92tamingthe,
>  >    author = {Guillermo Juan and Guillermo Juan Rozas},
>  >    title = {Taming the Y operator},
>  >    booktitle = {In ACM Conference on LISP and Functional Programming},
>  >    year = {1992},
>  >    pages = {226--234},
>  >    publisher = {ACM Press}
>  > }
>  >  ``In this paper I present a set of conceptually simple but involved
>  > techniques used by Liar 1 , the MIT Scheme compiler, to generate good
>  > code when recursive procedures are specified in terms of suitable
>  > versions of the Y operator. The techniques presented are
>  > general-purpose analysis and optimization tools, similar to well-known
>  > techniques used in the analysis and optimization of applicative
>  > languages, that combine synergistically to enable Liar to generate
>  > identical machine code for ordinary recursive definitions written
>  > using letrec and those written using suitable forms of Y.''
>  >
>  > ;; Allow compiler to inline standard procedures.
>  > (declare (usual-integrations))
>  >
>  > (define-syntax U
>  > (syntax-rules ()
>  >   ((_ f) (f f))))
>  >
>  > (define-syntax define/comb
>  > (syntax-rules ()
>  >   ((_ comb name (arg1 arg2) body)
>  >    (define name
>  >      (comb (lambda (name) (lambda (arg1 arg2) body)))))))
>  >
>  > ;; Allow compiler to inline Z
>  > (define-integrable (Z f)
>  > (U (lambda (g) (lambda (x y) ((f (U g)) x y)))))
>  >
>  > (define/comb Z comb-sum (l t)
>  > (if (null? l) t (comb-sum (cdr l) (+ t (car l)))))
>  >
>  > (define (sum l t)
>  > (if (null? l) t (sum (cdr l) (+ t (car l)))))
>  >
>  > (define (test1)
>  >  (let ((start-time (runtime))
>  > 	(l (make-list 10000000 1)))
>  >    (let ((answer (comb-sum l 0)))
>  >      (- (runtime) start-time))))
>  >
>  > (define (test2)
>  >  (let ((start-time (runtime))
>  > 	(l (make-list 10000000 1)))
>  >    (let ((answer (sum l 0)))
>  >      (- (runtime) start-time))))
>  >
>  > (test1) => .11 seconds
>  > (test2) => .11 seconds
>  >
>  >
>  > -- 
>  > ~jrm
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