Which systems have shell without functions or without unset?

[Stepan Kasal]

Hello,
  the autoconf manual says
        "You cannot assume the support of unset."
But no OS is mentioned.

James Youngman once said:

: variable, but we cannot unset it since the V7 shell does not have an
: "unset" command.  "test" is present in V7 and supports -n but is not
: a shell builtin.  V7 /bin/sh does not support hash comments, but
: fortunately it supports :.

but Autoconf uses the # comment, so its clear that the V7 /bin/sh is not
among the targeted systems.

I think the manual should mention a system whiich has /bin/sh without
unset, to explain why unset is not allowed.

When we are at it, the situation about shell functions is similar.
The manual doesn't mention any system witch this deficiency.
(I understand that shell functions are not used in Autoconf 2, but will be
allowed for Autoconf 3.)

You might say that this information will soon become obsolete.
But even though Autoconf doesn't actively _collect_ historic information,
I think we should keep what we have.  In Autoconf 3, many limitations
will be removed ("#! /", shell functions, perhaps unset), but I think the
information should remain in autoconf.texi, commented out.
That's why it would be good make the current explanations complete.

Have a nice day,
        Stepan Kasal