From mboxrd@z Thu Jan  1 00:00:00 1970
Date: Sun,  4 Oct 2009 03:03:27 +1100
From: Sam Watkins <sam@nipl.net>
To: 9fans@9fans.net
Message-ID: <20091003160327.GA15021@nipl.net>
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Subject: [9fans] mishandling empty lists - let's fix it
Topicbox-Message-UUID: 7cd4521a-ead5-11e9-9d60-3106f5b1d025

hi,

I wanted to have a whinge about one fault I find in unix: commands such as cat,
grep etc. do not handle an empty argument list correctly.  For example,

  cat

should output nothing and exit - concatenating 0 files.  Instead it copies
stdin to stdout, which is inconsistent.  This problem still exists in plan 9.

Copying stdin should be coded as:

  cat -

Such syntax would provide useful extra capability:

  find -type d | cat lib/emptydirs - | mail 9fans@9fans.net

Although this bug is not annoying for command-line work, consider a script that
processes all .c files to be found using cat or grep:

  find -name '*.c' | xargs cat | cc -     # this clever cc can handle it :)

This program works fine until there are no .c files to be found, in that case
it hangs, waiting for one on stdin!  This is a hazard to shell scripters, and a
potential source of security holes.  It's worse than cat -v.

Another example:

  8c && echo 1

should compile 0 files to give an empty object file, and echo 1.

Is there any chance we could fix these things in plan 9/inferno?
I feel that freedom from past mistakes is a key principle of plan 9.

If people support this change, I would be keen to work on it.

thanks!

Sam


(I noticed the "pike" language has a similar bug, `+(1,2,3) -> 6
but `+() -> error!  `+() should be 0 and `*() should be 1, of course.)
I don't think such bugs exist in Lisp :)