Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!hellgate.utah.edu!cdr.utah.edu!moore
From: moore%cdr.utah.edu@cs.utah.edu (Tim Moore)
Newsgroups: comp.lang.lisp
Subject: Re: read-from-string problem
Keywords: read-from-string, keyword arguments
Message-ID: <1990Dec20.090713.24536@hellgate.utah.edu>
Date: 20 Dec 90 16:07:13 GMT
References: <1990Dec20.115130.20493@cs.nott.ac.uk>
Organization: University of Utah CS Dept
Lines: 37

In article <1990Dec20.115130.20493@cs.nott.ac.uk> nigel@psyc.nott.ac.uk (Nigel Major) writes:
>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

READ-FROM-STRING takes two optional parameters, EOF-ERROR-P and
EOF-VALUE, like most reader functions. You were unwittingly supplying
values for those parameters, so in your first example you only
specified a value for :end (but not :start), and vice versa for the
second example.
>
>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.

They do. Both calls should return C:

(read-from-string "abcdefgh" nil nil :end 3 :start 2)
C
3

Tim Moore                    moore@cs.utah.edu {bellcore,hplabs}!utah-cs!moore
"Ah, youth. Ah, statute of limitations."
		-John Waters