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From: lpznigel@clan.nott.ac.uk (Nigel Major)
Newsgroups: comp.lang.lisp
Subject: read-from-string problem
Summary: keyword behaviour with read-from-string is unusual
Keywords: read-from-string, keyword arguments
Message-ID: <1990Dec20.115130.20493@cs.nott.ac.uk>
Date: 20 Dec 90 11:51:30 GMT
Sender: news@cs.nott.ac.uk
Reply-To: nigel@psyc.nott.ac.uk (Nigel Major)
Followup-To: comp.lang.lisp
Organization: AI Group, Dept. of Psychology, University of Nottingham
Lines: 28

Hello there,

In an effort to use read-from-string, I came across what
seemed to me to be pretty odd behaviour.  At first I thought
it was a bug in my Common Lisp (Lucid 3.0 on a Sun 4/110), but
the same thing happens in AKCL and Poplog CL, so I guess it
is not.  Would anyone like to explain it to me?

> (read-from-string "abcdefgh" :start 2 :end 3)
abc
3
> (read-from-string "abcdefgh" :end 3 :start 2)
cdefgh
8

I had rather assumed that the first call should return cd,
and that whatever the first call had returned, the second call
should return the same.  CLtL says of read-from-string that the
keywords :start and :end delimit a substring in the same way as
for other string functions.  However,

> (string= "abc" "xbc" :end2 2 :start1 1 :start2 1 :end1 2)
t

which seems to notice the start keywords and also not worry about
the order of the keywords.

Cheers, Nigel.