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## defun-c-callable

Arguments: name arglist &rest body

This macro is obsolete and has been replaced by defun-foreign-callable. Please use that macro in all new code. This macro is maintained for backward compatibility only.

This macro defines a function in Lisp that can be called from foreign (traditionally C) code.

The argument list can be restated as:

> > >     lisp-function-name ({arg | (arg type)}*) body-form+

Thus arglist (the second argument in the argument list) is a list of arguments each of which is either a symbol (as in the usual function definition), or it is a list of length two, a symbol and its type. If a symbol only is present, then it has the default type (`:signed-natural`). Each is an argument which C passes to Lisp. This macro does not allow &rest or &optional arguments in the argument list. The type corresponds to a memref type (see memref and memref-int) and is limited to be one of the following:

> > >     :signed-byte 8 bits
> > >     :unsigned-byte 8 bits
> > >     :signed-word 16 bits
> > >     :unsigned-word 16 bits
> > >     :fixnum 30 bits
> > >     :signed-long 32 bits
> > >     :unsigned-long 32 bits
> > >     :signed-natural (the default)
> > >     :unsigned-natural
> > >     :single-float, single-float 32 bits
> > >     :double-float, double-float 64 bits
> > >     :lisp (Assumes that C passes an actual Lisp value)

Warning for users of 64-bit Lisps: `:signed-long` and `:unsigned-long` are treated as 32-bit values, even on a 64-bit port. Contrast this to defun-foreign-callable, where `:long` and `:unsigned-long` match the precise meaning in C on the architecture in question. But note further that that does not mean they follow the 32/64-bit nature of the Lisp; for example, a `:long` foreign type on Compaq Alphas is always 64-bits, even for a 32-bit lisp. But this is consistent with C.

Warning about backward compatibility with release 5.0.1 and earlier: The default argument type is changed from `:signed-long` to `:signed-natural`. If a user has pre-6.0 code that explicitly specifies `:signed-long`, it is likely not to work on 64-bit ports, because `:signed-long` always specifies 32 bit values. If the user instead takes the default argument type, then the code will work in all 6.0 and pre-6.0 versions. If 32-bits is explicitly desired, however, then the `:signed-long` (or `:unsigned-long`) should be explicitly specified.

See memref and memref-int and foreign-functions.htm for general information on foreign functions in Allegro CL.

Copyright (c) 1998-2022, Franz Inc. Lafayette, CA., USA. All rights reserved.
This page was not revised from the 10.0 page.
Created 2019.8.20.

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| Allegro CL version 10.1 Unrevised from 10.0 to 10.1. 10.0 version