From: <dsmich@roadrunner.com>
To: guile-devel <guile-devel@gnu.org>, Hans Aberg <haberg-1@telia.com>
Subject: Re: Difference letrec & environment binding
Date: Wed, 13 Apr 2011 7:51:58 -0400 [thread overview]
Message-ID: <20110413115158.C5DYL.47361.root@cdptpa-web28-z01> (raw)
In-Reply-To: <DC011612-232F-47F3-A8AE-126FB2EDA02A@telia.com>
---- Hans Aberg <haberg-1@telia.com> wrote:
> What is the practical difference between the two ways of doing the same thing (letrec or an environment). Is letrec more efficient in the implementation of Guile?
>
> Hans
>
>
> (letrec (
> (even? (lambda (n)
> (if (zero? n) #t (odd? (- n 1)))))
> (odd? (lambda (n)
> (if (zero? n) #f (even? (- n 1))))))
> (even? 1000))
>
> ((lambda ()
> (define even? (lambda (n)
> (if (zero? n) #t (odd? (- n 1)))))
> (define odd? (lambda (n)
> (if (zero? n) #f (even? (- n 1)))))
> (even? 1000)))
>
No difference at all. Those generate identical code. I believe the second form is transformed into the first during compilation.
scheme@(guile-user)> ,x a
Disassembly of #<procedure a ()>:
0 (assert-nargs-ee/locals 8)
2 (br :L204) ;; -> 25 at (unknown file):15:9
6 (local-ref 0) ;; `n'
8 (make-int8:0) ;; 0 at (unknown file):16:8
9 (ee?)
10 (br-if-not :L205) ;; -> 16 at (unknown file):16:4
14 (make-true) ;; #t
15 (return)
16 (local-ref 0) ;; `n'
18 (sub1) at (unknown file):16:27
19 (local-set 0) ;; `n'
21 (br :L206) ;; -> 29 at (unknown file):16:21
25 (br :L207) ;; -> 48 at (unknown file):17:8
29 (local-ref 0) ;; `n'
31 (make-int8:0) ;; 0 at (unknown file):18:8
32 (ee?)
33 (br-if-not :L208) ;; -> 39 at (unknown file):18:4
37 (make-false)
38 (return)
39 (local-ref 0) ;; `n'
41 (sub1) at (unknown file):18:28
42 (local-set 0) ;; `n'
44 (br :L209) ;; -> 6 at (unknown file):18:21
48 (make-int16 3 232) ;; 1000
51 (local-set 0)
53 (br :L209) ;; -> 6 at (unknown file):19:2
scheme@(guile-user)> ,x b
Disassembly of #<procedure b ()>:
0 (assert-nargs-ee/locals 8)
2 (br :L216) ;; -> 25 at (unknown file):23:16
6 (local-ref 0) ;; `n'
8 (make-int8:0) ;; 0 at (unknown file):24:8
9 (ee?)
10 (br-if-not :L217) ;; -> 16 at (unknown file):24:4
14 (make-true) ;; #t
15 (return)
16 (local-ref 0) ;; `n'
18 (sub1) at (unknown file):24:27
19 (local-set 0) ;; `n'
21 (br :L218) ;; -> 29 at (unknown file):24:21
25 (br :L219) ;; -> 48 at (unknown file):25:15
29 (local-ref 0) ;; `n'
31 (make-int8:0) ;; 0 at (unknown file):26:8
32 (ee?)
33 (br-if-not :L220) ;; -> 39 at (unknown file):26:4
37 (make-false)
38 (return)
39 (local-ref 0) ;; `n'
41 (sub1) at (unknown file):26:28
42 (local-set 0) ;; `n'
44 (br :L221) ;; -> 6 at (unknown file):26:21
48 (make-int16 3 232) ;; 1000
51 (local-set 0)
53 (br :L221) ;; -> 6 at (unknown file):27:2
-Dale
prev parent reply other threads:[~2011-04-13 11:51 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-04-13 10:38 Difference letrec & environment binding Hans Aberg
2011-04-13 11:51 ` dsmich [this message]
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