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From: charest@ai-cyclops.jpl.nasa.gov (Len Charest)
Newsgroups: comp.lang.lisp
Subject: shadowing defstruct print-function
Message-ID: <1991May31.183953.29579@jpl-devvax.jpl.nasa.gov>
Date: 31 May 91 18:39:53 GMT
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Is it possible to shadow the print-function used to print a structure during a call to FORMAT? For example, suppose we have a structure FOO that prints using the print-function PRINT-FOO, i.e.,:
(format t "~a" foo)
=> #<FOO>
Now I want to locally redefine PRINT-FOO as in:
(flet ((print-foo (foo stream depth)
         (declare (ignore foo depth))
         (format stream "{Foo}")))
  (format t "~a" foo))
=> {Foo}
execpt that FLET only has lexical scope and the ~a FORMAT directive calls PRINT-FOO at a nested level where the global definition is active. So #<FOO> will really be printed. Any pointers?

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Len Charest, Jr.                                       charest@ai-cyclops.jpl.nasa.gov
JPL Artificial Intelligence Group
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