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