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Allegro CL version 10.0
Unrevised from 9.0 to 10.0.
9.0 version


Arguments: name &key nicknames nulls width

In releases prior to 6.1, there was a size keyword argument but no width or nulls arguments. The size argument confounded the width and nulls values. It is no longer accepted.

The arguments are:

This macro defines name as an external-format. If name already names an existing external-format, then that external-format is modified to have its nicknames, width, and nulls slots set to the values specified in the call to def-external-format. A slot is only modified in this call if it is specified in the call to def-external-format.

An error is signaled if any of the symbols specified in nicknames is a nickname to an external-format other than that being defined or modified.


(def-external-format :utf-8 :nicknames '(:utf8))

Here is an overview of how external-formats are used:

The main purpose for the external-format object is as a place to store Lisp coded procedures for translating octets in external representation to/from lisp strings. In order to use these routines as efficiently as possible, the translation procedures are defined as macros. The effect is that with these macros, the code to translate octets to and from characters is directly mixed in with the code to retrieve/store octets/characters. The macros themselves take as arguments expressions to get/put the next octet or character to translate. The return value of the macros' expansions are the number of octets or characters translated. (See def-char-to-octets-macro and def-octets-to-char-macro.)

Some external-formats may be composed with other external-formats to form new external-formats. For example, a wrapper external-format may be defined which combines external bytes representing 'f' and 'i' to create #\latin_small_ligature_fi. This wrapper external-format could be composed with the utf8 external-format to create a ligature-utf8 external-format. The wrapper external-format could also be composed with the euc external-format to create a ligature-euc external-format. Wrapped or composed external-formats are created using the compose-external-formats operator.

See iacl.htm for more information on international character support in Allegro CL.

Copyright (c) 1998-2019, Franz Inc. Oakland, CA., USA. All rights reserved.
This page was not revised from the 9.0 page.
Created 2015.5.21.

Allegro CL version 10.0
Unrevised from 9.0 to 10.0.
9.0 version