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## def-fwrapper

Arguments: name arglist &body body

Produces a form which returns name and defines an fwrapper as a side effect. This fwrapper is suitable for use as the fwrap-function in a call to fwrap.

name can be any function spec.

arglist is an ordinary lambda list. All ordinary lambda list keywords may be used, including &allow-other-keys, &aux, &key, &optional, and &rest. If either &key or &rest are present, then the arglist is automatically forced to be a list. (Note: the current implementation also forces a list when optional arguments are specified, because of some potential problems when a not-given optional argument is setq'd).

Argument accesses are provided for by means of symbol-macrolets, in a manner that is mostly intuitive. The arguments can simply be accessed by name, and they can be setq'd under most circumstances, with exceptions given below. The values of these setq'd arguments become part of the argument list that is sent to the next more inner fwrapper.

Exceptions:

- If the &rest arg is setq'd, the change only takes place for the current fwrapper, and is not passed inward. However, any changes made to the structure of the rest arg (via (setf car) or (setf cdr) or similar functions) will result in a change that will be passed inward.
- Any &key value that is setq'd will not replace or add the key value to the arglist that is passed inward, although the change will be in effect for the duration of the fwrapper.

#### def-fwrapper is a defining macro like defun

def-fwrapper is a additional defining macro in Allegro CL, joining the standard defining macros like defun. Among other things, this means that the resulting code is wrapped in a block named by the wrapper name which can be returned from. As with any defining macro, one can use macroexpand and pprint to see what is actually happening (you may see a different macroexpansion -- this is shown only to see how to get a macroexpansion):

    CL-USER(1): (pprint (macroexpand '(def-fwrapper foo (a b) nil)))

    (PROGN (EVAL-WHEN (COMPILE)
             (EXCL::CHECK-LOCK-DEFINITIONS-COMPILE-TIME 'FOO 'FUNCTION
               'DEF-FWRAPPER (FBOUNDP 'FOO)))
           (SETF (FDEFINITION 'FOO)
                 (NAMED-FUNCTION FOO
                   (LAMBDA (EXCL::NEXT-FWRAPPERS EXCL::FWRAP-ENV
                            EXCL::PRIMARY-FUNCTION ARGLIST EXCL::NARGS)
                     (DECLARE
                      (IGNORABLE EXCL::NEXT-FWRAPPERS EXCL::FWRAP-ENV
                       EXCL::PRIMARY-FUNCTION))
                     (EXCL::FWRAPPER-ARGUMENT-CHECK 'FOO 2 2 ARGLIST
                       EXCL::NARGS)
                     (BLOCK FOO
                       (SYMBOL-MACROLET ((A
                                          (EXCL::GET-FWRAPPER-ARG
                                           EXCL::NARGS
                                           0
                                           ARGLIST))
                                         (B
                                          (EXCL::GET-FWRAPPER-ARG
                                           EXCL::NARGS
                                           1
                                           ARGLIST)))
                         (LET* ()
                           (LET* ((#:G4 NIL))
                             (DECLARE (IGNORABLE #:G4))
                             NIL)))))))
           (REMPROP 'FOO 'EXCL::%FUN-DOCUMENTATION)
           (RECORD-SOURCE-FILE 'FOO) 'FOO)
    CL-USER(2):

See fwrappers-and-advice.htm for information of fwrapping functions (and on the older, deprecated advice facility).

Copyright (c) 1998-2019, Franz Inc. Oakland, CA., USA. All rights reserved.
This page was not revised from the 8.2 page.
Created 2012.5.30.

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