Thank you!
Sat, 28 Jun 2014 09:41:38 +0200 от "Jos Koot" <jos.k...@gmail.com>: >#lang racket > >(define-syntax (set!-values* stx) > (syntax-case stx () > ((_ (var ...) values-expr) > (with-syntax (((local-var ...) (generate-temporaries #'(var ...)))) > #'(let-values (((local-var ...) values-expr)) > (set!* var local-var) ...))))) > >(define-syntax (set!* stx) > (syntax-case stx () > ((_ var val) (free-identifier=? #'var #'_) #'foid) > ((_ var val) #'(set! var val)))) > >(define foid (void)) > >(define-values (a b c) (values 1 2 3)) >(set!-values* (_ _ c) (values 4 5 6)) >(list a b c) > >Jos > > >________________________________ > >From: users [mailto:users-boun...@racket-lang.org] On Behalf Of >Roman Klochkov >Sent: sábado, 28 de junio de 2014 8:43 >To: Racket Users List >Subject: [racket] Please help with syntax > > >I need to define syntax set!-values*, that will ignore _ in value >place. > >Such as >(define a #f) >(set!-values* (_ _ a) (values 1 2 3)) ; should set a to 3. > >But I have two problems: >1. _ don't want to pattern match in syntax case. If I make it >literal, I can't match "anything else". >2. How to omit extra values. It seems that in any case I have to >assign them to something... > >Can you help me? I hope, that my problem in fact not hard, but I >have not enough experience to solve it. > >-- >Roman Klochkov > > -- Roman Klochkov
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