#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:[email protected]] 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
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