((( [logo]Racket )))Need Help?
AboutDownloadDocumentationPLaneTCommunityLearning

[racket] "variadic"nested for?

From: J. Ian Johnson (ianj at ccs.neu.edu)
Date: Tue Mar 13 20:00:37 EDT 2012		 
What, like this?

(define-syntax-rule (myfor bindings (arity rhs) body)
  (let ([bindings (make-vector arity)])
    (let theloop ([i arity])
      (cond [(zero? i) body]
            [else
             (for ([a rhs])
               (vector-set! bindings (- arity i) a)
               (theloop (sub1 i)))]))))

>(myfor blah (3 '(0 1)) 
       (printf "~a" blah))
#(0 0 0)#(0 0 1)#(0 1 0)#(0 1 1)#(1 0 0)#(1 0 1)#(1 1 0)#(1 1 1)

----- Original Message -----
From: "rob cook" <heycarnut at gmail.com>
To: users at racket-lang.org
Sent: Tuesday, March 13, 2012 7:19:25 PM GMT -05:00 US/Canada Eastern
Subject: [racket] "variadic"nested for?


I'd like to be able to create a nested for where the depth of nesting is determined dynamically. 

For example, instead of 

(for* ((a '(0 1)) (b '(0 1))) (printf "~v~v " a b)) 

I could just say 

(myfor (2 '(0 1)) <body with some means of extracting nested values>). 

such that the above as (myfor (3 '(0 1)) <body with some means of extracting nested values>). would allow me to effect the result: 

((for* ((a '(0 1)) (b '(0 1)) (c '(0 1))) (printf "~v~v~v " a b c)) 

Thanks! 
Rob 


____________________
  Racket Users list:
  http://lists.racket-lang.org/users
Posted on the users mailing list.