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 <[email protected]>: > 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 > ____________________ > Racket Users list: > http://lists.racket-lang.org/users
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