Hi all, I've found that when using racket/class, one syntactic pain point I keep encountering is that the instantiation is clumsy. This is especially true if I want to mix different styles of instantiation (keyword and positional).
Is there any reason to not make the instantiation syntax of `new` more flexible? I most prefer `new` since it's the shortest and also most familiar of the three (the others being `make-object` and `instantiate`). In particular, I'm imagining the following syntax: (new c% 1 2 3) => (instantiate c% (1 2 3)) (new c% [x 1] [y 2]) => (instantiate c% [x 1] [y 2]) (new c% [z 3] 1 2) => (instantiate c% (1 2) [z 3]) (new c% 1 [z 3] 2) => (instantiate c% (1 2) [z 3]) and so on. Attached is a patch that implements this (modulo tests & docs). Any thoughts? Cheers, Asumu
>From cb0bfa789dc9d0a1c59f8090e9b967bb56f9ff9d Mon Sep 17 00:00:00 2001 From: Asumu Takikawa <[email protected]> Date: Fri, 1 Feb 2013 15:09:51 -0500 Subject: [PATCH] Add more flexible instantiation syntax for `new` --- collects/racket/private/class-internal.rkt | 41 ++++++++++++++++------------ 1 file changed, 24 insertions(+), 17 deletions(-) diff --git a/collects/racket/private/class-internal.rkt b/collects/racket/private/class-internal.rkt index 2c03780..57d08e7 100644 --- a/collects/racket/private/class-internal.rkt +++ b/collects/racket/private/class-internal.rkt @@ -3808,24 +3808,31 @@ An example ;; instantiation ;;-------------------------------------------------------------------- +;; class instantiation syntax, allows mixed keywords and positionals (define-syntax (new stx) - (syntax-case stx () - [(_ cls (id arg) ...) - (andmap identifier? (syntax->list (syntax (id ...)))) - (quasisyntax/loc stx - (instantiate cls () (id arg) ...))] - [(_ cls (id arg) ...) - (for-each (lambda (id) - (unless (identifier? id) - (raise-syntax-error 'new "expected identifier" stx id))) - (syntax->list (syntax (id ...))))] - [(_ cls pr ...) - (for-each - (lambda (pr) - (syntax-case pr () - [(x y) (void)] - [else (raise-syntax-error 'new "expected name and value binding" stx pr)])) - (syntax->list (syntax (pr ...))))])) + (syntax-parse stx + [(_ cls arg ...) + (define-values (kw-args pos-args) + (parse-init-args #'(arg ...))) + (with-syntax ([(kw ...) kw-args] + [(pos ...) pos-args]) + (quasisyntax/loc stx + (instantiate cls (pos ...) kw ...)))])) + +(begin-for-syntax + ;; listof<syntax> -> (values listof<syntax> listof<syntax>) + ;; parses arguments for `new` and collects them into two lists + (define (parse-init-args stx) + (define stxs (syntax->list stx)) + (define-values (kw-args pos-args) + (for/fold ([kw-args '()] + [pos-args '()]) + ([stx stxs]) + (syntax-parse stx + [(kw:id arg) + (values (cons stx kw-args) pos-args)] + [arg (values kw-args (cons stx pos-args))]))) + (values kw-args (reverse pos-args)))) (define ((make-object/proc blame) class . args) (do-make-object blame class args null)) -- 1.7.10.4
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