This page is part of the web mail archives of SRFI 71 from before July 7th, 2015. The new archives for SRFI 71 contain all messages, not just those from before July 7th, 2015.
Here is another stupid but easy example.
> (define x 10)
>
(srfi-let ((a (begin (display "first") (newline) (set! x (+ x 1)) x))
(b c (values (begin (display "second") (newline) (set! x 1)
x)
(begin (display "third") (newline) (set! x 1000)
x)))
(d (begin (display "end") (newline) (set! x (+ x 11)) x)))
(set! x 10)
(list a b c d))
second
third
first
end
(1001 1 1000 1012) ---------------> different result
>
(let ((a (begin (display "first") (newline) (set! x (+ x 1)) x))
(b (begin (display "second") (newline) (set! x 1) x))
(c (begin (display "third") (newline) (set! x 1000) x))
(d (begin (display "end") (newline) (set! x (+ x 11)) x)))
(set! x 10)
(list a b c d))
first
second
third
end
(11 1 1000 1011) ---------------> different result
The SRFI-71 implementaion is too difficult for me to understand.
So I will show the followings.
(define-syntax alet
(syntax-rules ()
((alet (clause ...) body1 body2 ...)
(conversion () (clause ...) body1 body2 ...))
((alet name ((a b) ...) body1 body2 ...)
((letrec ((name (lambda (a ...) body1 body2 ...)))
name)
b ...))))
(define-syntax conversion
(syntax-rules ()
((conversion ((n v) ...) (((a) c) clause ...) body ...)
;; This is a bug site. --- ((values a) c) in srfi-71
;; (conversion ((n v) ... (a c)) (clause ...) body ...)
((lambda (a)
(conversion ((n v) ... (a a)) (clause ...) body ...)) c))
((conversion ((n v) ...) (((a . b) c) clause ...) body ...)
(dot-values ((n v) ...) ((((a) b) c) clause ...) body ...))
((conversion ((n v) ...) (((a . b) c d ...) clause ...) body ...)
(dot-simple ((n v) ...) ((((a) b) c d ...) clause ...) body ...))
((conversion ((n v) ...) ((a b) clause ...) body ...)
;; This is a bug site.
;; (conversion ((n v) ... (a b)) (clause ...) body ...)
((lambda (a)
(conversion ((n v) ... (a a)) (clause ...) body ...)) b))
((conversion ((n v) ...) ((a b c ...) clause ...) body ...)
(new-values ((n v) ...) (((a) (b c ...)) clause ...) body ...))
((conversion ((n v) ...) (a b clause ...) body ...)
(call-with-values (lambda () b)
(lambda a
(conversion ((n v) ... (a a)) (clause ...) body ...))))
((conversion ((n v) ...) () body ...)
((lambda (n ...) body ...) v ...))))
(define-syntax new-values
(syntax-rules ()
((new-values ((n v) ...) (((a ...) (a1 a2 a3 ...)) clause ...) body
...)
(new-values ((n v) ...) (((a ... a1) (a2 a3 ...)) clause ...) body
...))
((new-values ((n v) ...) (((a a1 ...) (b)) clause ...) body ...)
(call-with-values (lambda () b)
(lambda (a a1 ...)
(conversion ((n v) ... (a a) (a1 a1) ...) (clause ...) body
...))))))
(define-syntax dot-values
(syntax-rules ()
((dot-values ((n v) ...) ((((a1 ...) (a . b)) c) clause ...) body
...)
(dot-values ((n v) ...) ((((a1 ... a) b) c) clause ...) body ...))
((dot-values ((n v) ...) ((((a1 ...) ()) c) clause ...) body ...)
(call-with-values (lambda () c)
(lambda (a1 ...)
(conversion ((n v) ... (a1 a1) ...) (clause ...) body ...))))
((dot-values ((n v) ...) ((((a1 ...) b) c) clause ...) body ...)
(call-with-values (lambda () c)
(lambda (a1 ... . b)
(conversion ((n v) ... (a1 a1) ... (b b)) (clause ...) body
...))))))
(define-syntax dot-simple
(syntax-rules ()
((dot-simple ((n v) ...) ((((a1 ...) (a . b)) c d ...) clause ...)
body ...)
(dot-simple ((n v) ...) ((((a1 ... a) b) c d ...) clause ...) body
...))
((dot-simple ((n v) ...) ((((a1 ...) ()) c d ...) clause ...) body
...)
((lambda (a1 ...)
(conversion ((n v) ... (a1 a1) ...) (clause ...) body ...))
c d ...))
((dot-simple ((n v) ...) ((((a1 ...) b) c d ...) clause ...) body
...)
((lambda (a1 ... . b)
(conversion ((n v) ... (a1 a1) ... (b b)) (clause ...) body
...))
c d ...))))
--
Joo ChurlSoo