[racket] Compile-time evaluation

Try evcase 

On Jul 29, 2013, at 8:48 PM, Roman Klochkov wrote:

> 
> #. calcuclates its argument and place it in the program code.
> Now I have to write something like 
> 
> (case state-number
>   ((0 1) ; state in init, stage1
>      (initialize))
>    ((2) ; state = process
>        (function1)
>    ((3) ; state = abort
>        (function2)))
> 
> I want to have
> 
> (define (state x)
>   (let rec ([states '(init stage1 process fail)]
>             [pos 0])
>     (cond
>       [(null? states) #f]
>       [(eq? (car states) x) pos]
>       [else (rec (cdr states) (add1 pos))])))
> 
> (case state-number
>   ((#.(state 'init) #.(state 'stage1))
>      (initialize))
>    ((#.(state 'process))
>        (function1)
>    ((#.(state 'fail))
>        (function2)))
> 
> So the code becomes self-documenting. Like using enum values in C or Pascal.
> 
> Понедельник, 29 июля 2013, 13:32 -04:00 от Asumu Takikawa <asumu at ccs.neu.edu>:
> On 2013-07-29 06:25:21 +0400, Roman Klochkov wrote:
> > Is there simple way to calculate during compilation. Something like #.
> > in Common Lisp.
> 
> Can you tell us what #. means in Common Lisp?
> 
> I am guessing that you want to do something like the following:
> 
>   #lang racket
>   (require (for-syntax syntax/parse))
> 
>   ;; functions to compute costly constants
>   ;; at compile-time
>   (begin-for-syntax
>     (define (compute-x) ...)
>     (define (compute-y) ...)
>     (define (compute-z) ...))
> 
>   ;; macro that defines x, y, z assuming
>   ;; suitable definitions of compute-x, etc.
>   (define-syntax (define-constants stx)
>     (syntax-parse stx
>       [(_ x:id y:id z:id)
>        #`(begin (define x #,(compute-x))
>                 (define y #,(compute-y))
>                 (define z #,(compute-z)))]))
> 
>   (define-constants my-x my-y my-z)
> 
> This will work if the `compute-` functions produce flat data that can be
> embedded in syntax, like numbers.
> 
> Cheers,
> Asumu
> 
> 
> -- 
> Roman Klochkov
> 
> 
> -- 
> Roman Klochkov
> ____________________
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>  http://lists.racket-lang.org/users

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