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

Did you consider make-hash, hash-get, and hash-set! and friends?

Robby

On Tue, Oct 14, 2008 at 11:33 PM, Fred G. Martin <fredm at cs.uml.edu> wrote:
> 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 --
> http://blog.plt-scheme.org/2007/11/getting-rid-of-set-car-and-set-cdr.html.
>
> Is this code really the right way to go?  Or is there a much simpler
> (built-in?) version of this? (code below).
>
> Fred
>
>
> (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)
>                  #f))
>            #f)))
>    (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)))))
>      'ok)
>    (define (dispatch m)
>      (cond ((eq? m 'lookup-proc) lookup)
>            ((eq? m 'insert-proc!) insert!)
>            (else (error "Unknown operation -- TABLE" m))))
>    dispatch))
>
> (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
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