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implementing 'atomic' designation

daemon@ATHENA.MIT.EDU (Wed Sep 21 21:19:52 1994 )

From: stewarta@netcom.com (Alex Stewart)
To: coldstuff@MIT.EDU
Date: Wed, 21 Sep 1994 18:08:53 -0700 (PDT)

Well, as people have probably already surmised by now I'm getting back into the
ColdMUD arena with a vengeance :).  I've got a few more server mods I'd like to
see and will probably be looking into unless people have real problems with

First, it seems to me that now that we have the ability to pause and
suspend, somebody should also implement the ability to designate code blocks as
being atomic pretty soon to go with it, before we end up with a lot of code
that won't adapt well to that way of doing things when it finally gets
implemented (and I do think it should be)..

I'm not really sure how Greg intended the atomic designation to work from a
linguistic standpoint (Greg, you out there?  got any suggestions?).  I know he
reserved some keywords for it.  My inclination would be to do it something

  atomic statement;


  atomic {

(so that 'atomic' is syntactically and procedurally equivalent to an
'if (1)', just with the additional effect that the associated statement is
executed atomically)..  The other question is how suspending operations should
act when they're attempted in an atomic execution state..  suspend() I suppose
would have to throw an error in any case.  pause() should presumably do
likewise (the alternative being to simply continue on without pausing, but this
would probably be bad).

I think I'll look into what's required to do this next unless someone else is
already working on it.  Any comments about my proposed syntax/results?

Also, there are still a couple of operators I'd like to see in the language in
some form or other (though I am somewhat negotiable on these points).  Would
people have objections to creating an assignment-expression operator which
is distinct from simple assignment (which isn't an expression), for use in
things like while loops? (If not, what should it be?  ':=' I suppose is a
possibility but I suppose Pascal-types might end up using that in place of the
'=' operator all the time, thus eliminating the protective aspects of normal
assignment..  hmm..).  The only real reason I want such a thing is for while
loops, but I really can't think of any other way to deal with them cleanly..

Although.. I suppose an alternative might be to introduce a ',' (comma)
operator, like in C ('foo, bar, baz' executes the foo statement, the bar
statement and the baz statement and returns the value of the last (baz)
statement as the value of the entire expression)..  That would allow things
like 'while (x = foo(), x) { ... }', etc.

The other thing that I think would be nice would be an operator (for now I'll
call it '??', tho I'm not really sure about what it should actually look like)
such that:

  foo = bar ?? baz;

would be equivalent to:

  x = bar;
  foo = (type(x) != 'error) ? x | baz;

(i.e. return the value of bar unless it's an error value, in which case return
baz instead.  This makes it work similarly to ||, but testing error condition
rather than truth value.  Thus a lot of common 'catch any' conditions could be
written a lot more cleanly as things like 'foo = (| bar |) ?? baz;', etc.)

Anyway, comments/suggestions anyone?

   Alex Stewart - stewarta@netcom.com - Richelieu @ Diversity University MOO