[plt-scheme] can't run SICP "generic operations" code in PLT Scheme 4.1

From: Fred G. Martin (fredm at cs.uml.edu)
Date: Wed Oct 15 00:33:06 EDT 2008

Mmm OK, I modified the make-table procedure to use mutable-pairs and
lists, and it works now.

I also found the nice blog entry about why mutable pairs (at least the
default ones) are bad --

Is this code really the right way to go?  Or is there a much simpler
(built-in?) version of this? (code below).


(define (make-table)
  (let ((local-table (mlist '*table*)))
    (define (lookup key-1 key-2)
      (let ((subtable (massoc key-1 (mcdr local-table))))
        (if subtable
            (let ((record (massoc key-2 (mcdr subtable))))
              (if record
                  (mcdr record)
    (define (insert! key-1 key-2 value)
      (let ((subtable (massoc key-1 (mcdr local-table))))
        (if subtable
            (let ((record (massoc key-2 (mcdr subtable))))
              (if record
                  (set-mcdr! record value)
                  (set-mcdr! subtable
                            (mcons (mcons key-2 value)
                                  (mcdr subtable)))))
            (set-mcdr! local-table
                      (mcons (mlist key-1
                                  (mcons key-2 value))
                            (mcdr local-table)))))
    (define (dispatch m)
      (cond ((eq? m 'lookup-proc) lookup)
            ((eq? m 'insert-proc!) insert!)
            (else (error "Unknown operation -- TABLE" m))))

(define operation-table (make-table))
(define get (operation-table 'lookup-proc))
(define put (operation-table 'insert-proc!))

On Tue, Oct 14, 2008 at 11:19 PM, Woodhouse Gregory
<gregory.woodhouse at gmail.com> wrote:
> Since pairs are no longer mutable in PLT Scheme, you can't use set-cdr! You
> probably want to use mutable pairs instead.
> "The art of asking the right questions in mathematics is more important than
> the art of solving them."
> --Georg Cantor
> http://www.gwoodhouse.com
> http://GregWoodhouse.ImageKind.com
> On Oct 14, 2008, at 7:59 PM, Fred G. Martin wrote:
> Hey all,
> I can't figure out which language pack/ include statement / other
> setting is necessary to run the generic operations package from SICP.
> Here are two samples of the code I'm trying to run:
> http://www.cs.uml.edu/~holly/91.301/ps6-code.ss
> http://rlai.cs.ualberta.ca/325assignment5.html
> The code works fine in PLT-Scheme 3.72 (setting "Textual (MzScheme,
> includes R5RS)" but I am stumped trying to get it to run in 4.1.
> In general 4.1 seems to not like redefining stuff... I must admit I am
> mystified by all the language choices.
> Thanks for your help,
> Fred
> _________________________________________________
>   For list-related administrative tasks:
>   http://list.cs.brown.edu/mailman/listinfo/plt-scheme

Posted on the users mailing list.