[racket] Help with phases

Yes that is my understanding.

On 01/17/2012 01:43 AM, Veer Singh wrote:
> Thanks , I think I understand it now  , so roughly following steps happens(apology for incorrect terminology) :
>
> 1. bind the identifier 'phases' to some val(a syntax transformer) in phase 1
>
>     i)  during the above step id 'phase2' is bound to some val i.e syntax transformer in phase 2 
>
>     ii) (phase2) is expanded i.e it is looked up in phase 2 and it's syntax transformer applied , which returns the syntax object which is basically #'0 
>          since cnt was 0 at the time of application of transformer.
>
>    iii)  step 1 done.
>
>
>
> 2. encounters macro call (set-compile) and expansion takes place and set cnt=1(phase 1) , cnt=2(phase 2).
>
> 3. encounters macro call (phases) looks up in phase 1 and its transformer is applied and we get (list 1 0) , since
>    (p1 cnt=1) and (p2 0).
>  
>
>
> On Tue, Jan 17, 2012 at 12:51 PM, Jon Rafkind <rafkind at cs.utah.edu <mailto:rafkind at cs.utah.edu>> wrote:
>
>     I'm guessing a little bit but I think its because the `phases' macro is expanded at phase 2 before `set-compile' is called. If you put (set-compile) before the definition of `phases' then you get '(1 2).
>
>
>     On 01/17/2012 12:06 AM, Veer Singh wrote:
>>
>>     Why macro call (phases) produces '(1 0) and not '(1 2) ?
>>
>>
>>     (module mod1 racket
>>     (require (for-syntax syntax/parse))
>>                          ;"mod-compile.rkt"))
>>     (require (for-syntax 
>>               (for-syntax syntax/parse racket )))
>>                           ;"mod-compile.rkt")))
>>     (provide set-compile phases)
>>
>>       ;For phase 1
>>       (begin-for-syntax
>>         (define cnt 0)
>>         
>>       (define (store! v)
>>         (set! cnt v)))
>>       
>>       ;For phase 2
>>       (begin-for-syntax (begin-for-syntax
>>         (define cnt 0)
>>         
>>       (define (store! v)
>>         (set! cnt v))))
>>       
>>       ;;set the value of "cnt" in phase1 and phase2
>>       (define-syntax (set-compile stx)
>>         (syntax-parse stx
>>           [(_) #'(begin
>>                    
>>                    (begin-for-syntax
>>                      ; in "cnt" in phase 1 cnt=1
>>                      (store! 1) 
>>                      (begin-for-syntax
>>                        ; in "cnt" in phase 2 cnt=2
>>                        (store! 2)))
>>                    'done)]))
>>       
>>
>>       ;;return the value of cnt in phase1 and phase2
>>       (define-syntax (phases stx)
>>         
>>         ;phase2 ???
>>         (define-syntax (phase2 stx)              
>>           (syntax-parse stx
>>             [(_) (with-syntax ([p cnt])
>>                    #'p)]))
>>                      
>>                      
>>         ;phase1    
>>         (syntax-parse stx
>>           [(_) (with-syntax ([p1 cnt]
>>                              [p2 (phase2)])
>>                  #'(list p1 p2))]))
>>       
>>       (set-compile)
>>       (phases)
>>       ;produces (list 1 0), but why not (list 1 2) 
>>       
>>     )
>>
>>
>>     Thanks
>>
>>
>>
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