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#lang racket/base
(require (for-syntax racket/base
racket/syntax
syntax/parse
racket/list)
racket/list)
(provide define-parameter-group parameterize/group parameterize*/group)
(begin-for-syntax
(struct parameter-group (ids) #:transparent
#:property prop:procedure
(λ (g stx)
(syntax-case stx ()
[(_)
(with-syntax ([(ids ...) (parameter-group-ids g)])
(syntax/loc stx
(list (ids) ...)))]))))
(define-syntax (define-parameter-group stx)
(syntax-parse stx
[(_ name:id (param:id ...))
(syntax/loc stx
(define-syntax name (parameter-group (list #'param ...))))]))
(define-for-syntax (make-list-ref val i)
(cond [(= i 0) #`(car #,val)]
[else (make-list-ref #`(cdr #,val) (- i 1))]))
(define-for-syntax (expand-parameter-groups id val)
(define group (syntax-local-value id (λ () #f)))
(if (and group (parameter-group? group))
(let ([ids (parameter-group-ids group)])
(append*
(map (λ (id i) (expand-parameter-groups id (make-list-ref val i)))
ids
(build-list (length ids) values))))
(list #`[#,id #,val])))
;; Corresponds to parameterize
(define-syntax (parameterize/group stx)
(syntax-parse stx
[(_ ([p:id v] ...) . body)
(with-syntax* ([(v-name ...) (generate-temporaries #'(v ...))]
[([p new-v] ...) (append* (map expand-parameter-groups
(syntax->list #'(p ...))
(syntax->list #'(v-name ...))))])
(syntax/loc stx
(let ([v-name v] ...)
(parameterize ([p new-v] ...) . body))))]))
;; Corresponds to parameterize*
(define-syntax parameterize*/group
(syntax-rules ()
[(_ () . body)
(let () . body)]
[(_ ([lhs1 rhs1] [lhs rhs] ...) . body)
(parameterize/group ([lhs1 rhs1]) (parameterize*/group ([lhs rhs] ...) . body))]))
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