break label stuff

[Rob Warnock]

+---------------
| I can't keep track of all the variations of the break syntax.
| None of them have the immeadate clarity I'm use to in codeing in C.
| Could someone point me at a language that has labeled loops
| without gotos?  I do prefer structured languages.  But I don't
| agree with the compleate banishment of the unrestricted branch.
+---------------

The BLISS language, which is about as old as "C", has no
"goto" at all. ("Never did, never will...") It DOES have the
"leave <label>" construct, where the label can be put on ANY block,
not just loops. (Since it is an expression language, you can also
"leave <label> with <value>", and of course, "return <value>" is
just shorthand for "leave <current-procedure> with <value>".)

+---------------
| In any language, I consider the goto statement perfectly valid
| for use to branch out of a nested construct to following code.
| (Stay within the same procedure of course.)
+---------------

Yes, but C's "goto" allows branching INTO nested constructs, too.

+---------------
|                  ... What do the labeled loop people think of
| breaking switches?...
| Is this analogous or allowed?
| flagsw:	switch (*argv[1]) {
| 	case 's':
| 		switch (*argv[2]) {
| 		case 'b':
| 			break flagsw;
| 		...
| 		}
| 	...
| 	}
| /* execution comes here after the break */
+---------------

This is PRECISELY what the BLISS "leave" does.

+---------------
| I strongly object to this type of labeled switch.
| I don't think that the language change should be made unless it is
| uniform, and I don't think that a compromise can be made between
| loop labeling and switch labeling.  Carefull use of gotos is
| clearer and more consistant I think.
| Jeff Anton |	U.C.Berkeley |	ucbvax!anton |	anton at berkeley.ARPA
+---------------

The key is going far enough in making the language construct uniform.
Remember, everything a "leave" can do, a "goto" can already do in C.
(Just put the label AFTER the second right bracket.) If you object to
using a "leave" in the above case you must ALSO object to using a "goto",
to be honest. It is easier to be "careful" if the language contains
constructs which restrict what you can do to what you need in a particular
situation. (That's why we have "for" and "while" and "switch" at all!)

When you see a "goto" in the text, you normally have NO IDEA where it's
going without reading the rest of the program. When you see a labelled block,
you immediately know that it's going to be left (otherwise there would
be no label), so you can keep that in mind as you read. When you see the
"leave", you know what scope is being left (you don't have to count
right-brackets).

The incidence of the "goto" in C code is so rare anyway, I dare say
we could abolish it altogether (replacing it with BLISS's "leave")
and not miss the loss. (I certainly never missed it in BLISS.)


Rob Warnock
Systems Architecture Consultant

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