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From: ok@goanna.cs.rmit.oz.au (Richard A. O'Keefe)
Newsgroups: comp.lang.scheme
Subject: Re: looking for balancing (binary/avl) tree programs
Message-ID: <5898@goanna.cs.rmit.oz.au>
Date: 22 May 91 08:05:14 GMT
Article-I.D.: goanna.5898
References: <5863@goanna.cs.rmit.oz.au> <9105210031.aa21207@mc.lcs.mit.edu>
Organization: Comp Sci, RMIT, Melbourne, Australia
Lines: 51

I wrote
>    The thing that really worries me is that the last line of the file that
>    I picked up was incomplete.  It read
>    "          (case-3)))))"
>    (minus the quotes), and the file just *stopped* at that point without
>    even the LF that one expects to terminate every line.  Is anything more
>    than the LF missing?

In article <9105210031.aa21207@mc.lcs.mit.edu>, cph@altdorf.ai.mit.EDU (Chris Hanson) writes:
> There's nothing else missing.  I never add a final newline to a Scheme
> source file, because Scheme doesn't require it.  I refuse to give in
> to the short-sighted unix designers who have decided that every file
> should end in a newline.

These days, due largely to the influence of UNIX, we expect a file to be
a sequence of ``bytes''.  That works fine under UNIX, although as I
mentioned a lot of tools don't quite believe it, and it works fine on
Macintoshes.  It doesn't quite work under MS-DOS, where traces of CP/M
influence still linger.  It doesn't work under VMS.  VMS's "native"
file formats are all record oriented.  VMS does have "stream" record
formats (STREAM, STREAM_LF, STREAM_CR) which basically mimic the UNIX
kind of model, but RMS still requires each "record" thus delimited to
be at most 32k bytes long.  MVS/TSO and VM/CMS are very much record
oriented; their record formats (like VMS's "native" formats) do not
admit an unterminated record as a logical possibility.

It's not a matter of giving in to "unix designers", it's a matter of
not giving a tinker's for portability or for people who might want to
read your files into other file systems, let alone try to use what
you write.

I wouldn't be too sanguine about Scheme not requiring terminated lines,
either.  Common Lisp has an operation called "read-line", and from
p572 of CLtL2, "read-line reads in a line of text TERMINATED BY A NEWLINE".
What relevance has this to Scheme?  Well, several Schemes provide
read-line (though some call it read-string).  Scheme not having multiple
results, the Scheme versions of read-line that I've seen are even pickier
about proper termination than CL.

And at a minimum, leaving the last line of a file unterminated is a
discourtesy to human readers.  The result looks exactly like a file
which has been truncated at an inappropriate point by a mailer or a
broken 'tar' or a file system which filled up while the file was
being written (given the state of my 'quota', a very likely event),
and so on.  Some considerate programmers go so far as to include a
little comment like ";; eof" at the end of their files.  Don't think
I haven't had occasion to be grateful for that.  Another couple of
times and I'll start doing it myself.

-- 
There is no such thing as a balanced ecology; ecosystems are chaotic.