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Date: Mon, 23 May 88 22:55:49 edt
From: jinx at CHAMARTIN.AI.MIT.EDU (Guillermo J. Rozas)
MIT Scheme has a procedure (rather than a special form) called
DYNAMIC-WIND, which is a generalization of UNWIND-PROTECT.
(lambda () <entry>)
(lambda () <body>)
(lambda () <exit>))
is similar to
(let ((val <body>))
except that <exit> is executed whenever <body> is "escaped", and
<entry> is executed whenever <body> is (re)entered.
T has this too; it's called BIND-HANDLER, and behaves the same way.
(UNWIND-PROTECT body . exit) is sugar for (BIND-HANDLER FALSE (LAMBDA ()
body) (LAMBDA () . exit)). The BIND macro is also sugar for a use of
BIND-HANDLER, thus the name.