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;; Copyright (c) 2009 Derick Eddington. All rights reserved.
;; Licensed under an MIT-style license. My license is in the file
;; named LICENSE from the original collection this file is distributed
;; with. If this file is redistributed with some other collection, my
;; license must also be included.
;; Fall-back library in case the host Scheme system does not provide SRFI-39.
(library (surfage s39 parameters)
(define make-parameter
[(val) (make-parameter val values)]
[(val guard)
(unless (procedure? guard)
(assertion-violation 'make-parameter "not a procedure" guard))
(let ([p (case-lambda
[() val]
[(x) (set! val (guard x))])])
(p val)
(define-syntax parameterize
;; Derived from Ikarus's implementation of parameterize.
(lambda (stx)
(syntax-case stx ()
[(_ () b0 b ...)
#'(let () b0 b ...)]
[(_ ([p e] ...) b0 b ...)
(with-syntax ([(tp ...) (generate-temporaries #'(p ...))]
[(te ...) (generate-temporaries #'(e ...))])
#'(let ([tp p] ...
[te e] ...)
(let ([swap (lambda ()
(let ([t (tp)])
(tp te)
(set! te t))
(lambda () b0 b ...)
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