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From: tchrist@convex.com (Tom Christiansen)
Newsgroups: comp.lang.perl
Subject: dynamic formats
Message-ID: <5195@convex.convex.com>
Date: 6 Feb 90 17:39:37 GMT
Sender: news@convex.com
Reply-To: tchrist@convex.com (Tom Christiansen)
Organization: Convex Computer Corp, Richardson, TX
Lines: 62

I've been using formatted writes and I find that it's a real
pain to be forced to associate one sole format() with a 
given output channel.  I've tried Johan Vromans's indirect-thru-
a-subroutine work-around:

   format =
   @<<< @<<< @<<< @<<<
   $_[0], $_[1], $_[2], $_[3]
   .

   sub fmt_write {
           write;
   }

   &fmt_write("A", 1, 2, 3);

which works ok, but not quite what I'd like.

I think what I'd most like is something just *mildly* more similar
to FORTRAN's write statements.  I'd like to be able to dynamically
specify *which* format to use.  The documentation on format has

    format NAME
	picture
    .

When you first look at that, you figure you should be able to use:

    format FOOFORM
	blah
    .

    write FOOFORM;  # use FOOFORM to write to current output channel

except that NAME really means a FILEHANDLE in this case.  Formats
don't really have their own namespace, and I wish they did.

I'm trying to figure out a way to extend the syntax without breaking
anything.  If write's syntax were

	write(FILEHANDLE);
    or	
	write(FILEHANDLE, FORMAT);

where FORMAT were the name of a tagged format field, it could work.
(Assume either FILEHANDLE or FORMAT could be scalar expressions 
for indirection.)  

But how to tag the format?  We (probably) can't use

	format TAG

because you couldn't (easily) disambiguate the TAG from a FILEHANDLE.

Comments, criticisms, or inspirations anyone?

--tom
--

    Tom Christiansen                       {uunet,uiucdcs,sun}!convex!tchrist 
    Convex Computer Corporation                            tchrist@convex.COM
		 "EMACS belongs in <sys/errno.h>: Editor too big!"