#. 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
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