Re: code critique

Daniel Leidisch <news@xxxxxxxxxxxx> writes:
In article <87r6oyigvo.fsf@xxxxxxxxxxxxxxxxxx> you wrote:

* A portability caveat: ANSI Common Lisp does not require
characters to be encoded in ASCII or any other encoding, and so
CODE-CHAR may not do what you expect here.

Do you have any suggestions as to how to implement this
more portably?

Well, this was mostly a fussy "technically this isn't portable" note;
all current implementations do, I think, use a superset of ASCII for
their character repertoires.

In case you are interested in being fussy: a conforming ANSI CL
implementation is only required to support the 96 characters in the
standard-character repertoire, and one of those characters, Newline,
need not map to a single ASCII character. You can get the standard
character for an ASCII code like this:

(defun ascii-code-char (code)
(cond ((< 31 code 127)
(char #.(format nil "~@{~A~}"
" !\"#$%&’()*+,-./0123456789:;<=>?@"
"ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`"
"abcdefghijklmnopqrstuvwxyz{|}~")
(- code 32)))
(t ;Here you might handle Newline and the semistandard characters
(error "Can't find an ASCII character for code ~D" code))))

For the other characters in the ASCII character set, you'll need to
resort to implementation-dependent details. For Unicode, RFC 3986
defines the URL encoding of a Unicode code point as the URL encoding
of the octets in the UTF-8 encoding of the code point, so if you care
to support this, you'll probably have make your decoder a bit more
complex. (A quick check leaves me less than confident that all
browsers actually encode Unicode code points according to the RFC,
though.)

--
RmK
.

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