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; "fluidlet.scm", FLUID-LET for Scheme
; Copyright (c) 1998 Aubrey Jaffer
;
;Permission to copy this software, to modify it, to redistribute it,
;to distribute modified versions, and to use it for any purpose is
;granted, subject to the following restrictions and understandings.
;
;1. Any copy made of this software must include this copyright notice
;in full.
;
;2. I have made no warranty or representation that the operation of
;this software will be error-free, and I am under no obligation to
;provide any services, by way of maintenance, update, or otherwise.
;
;3. In conjunction with products arising from the use of this
;material, there shall be no use of my name in any advertising,
;promotional, or sales literature without prior written consent in
;each case.
(require 'dynamic-wind)
;@
(defmacro fluid-let (clauses . body)
(let ((ids (map car clauses))
(new-tmps (map (lambda (x) (gentemp)) clauses))
(old-tmps (map (lambda (x) (gentemp)) clauses)))
`(let (,@(map list new-tmps (map cadr clauses))
,@(map list old-tmps (map (lambda (x) #f) clauses)))
(dynamic-wind
(lambda ()
,@(map (lambda (ot id) `(set! ,ot ,id))
old-tmps ids)
,@(map (lambda (id nt) `(set! ,id ,nt))
ids new-tmps))
(lambda () ,@body)
(lambda ()
,@(map (lambda (nt id) `(set! ,nt ,id))
new-tmps ids)
,@(map (lambda (id ot) `(set! ,id ,ot))
ids old-tmps))))))
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