Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!watmath!clyde!burl!ulysses!bellcore!petrus!scherzo!allegra!mit-eddie!think!harvard!seismo!rochester!bullwinkle!uw-beaver!fluke!ssc-vax!savage
From: savage@ssc-vax.UUCP (Lowell Savage)
Newsgroups: net.lang
Subject: Re: and if you put this in your languag
Message-ID: <685@ssc-vax.UUCP>
Date: Thu, 3-Apr-86 20:06:44 EST
Article-I.D.: ssc-vax.685
Posted: Thu Apr  3 20:06:44 1986
Date-Received: Tue, 8-Apr-86 06:16:25 EST
References: <1187@mmintl.UUCP>  <6925@cca.UUCP>
Organization: Boeing Aerospace Co., Seattle, WA
Lines: 60

The discussion was "structured programming" and goto's in code.
Richard Harter proposed a "new" type of programming language feature
to take care of the case where goto's are most commonly used in HOL's.
This case is (for those who have not been following the discussion or
have forgotten by now), to use a goto statement to 'escape' from several
levels of nested block and control structures.

> ... I would like to have the following structures available:
> 
> 	BLOCK label_name {
> 	  .....
> 	  }
> 
> 	LOOP label_name {
> 	  .....
> 	  }
> 
> 	FRAGMENT label_name {
> 	  .....
> 	  }
> 
> A FRAGMENT is essentially an internal procedure without arguments;
> a BLOCK is a labelled block of code; and a LOOP is a labelled (forever)
> loop.  The command statement that I want is:
> 
> 	escape [(block/loop)_label_name] [via fragment_name]
> 
> This statement transfers control to the next statement after the
> block (loop) but first executes the named fragment.  If there is
> no block/loop label name the escape leaves the current block/loop.
> If there is no via clause control is transferred directly to the
> next statement.  Every once in a while I find that I would really
> like to have something like this available.

I beleve that Ada provides such a facility (with an "exit" statement
which can take arguments that are block names) only without the
FRAGMENT capability.  If there is some set of code that needs to be
executed before the block is exited, then that code can come before
the exit statement.  However, Ada also provides another mechanism
which I think can be used for complete purpose intended by Richard.
This is the exception mechanism.  The FRAGMENT is now the statements
after the exception handler, and the "exit" or "escape" statement is
now the Ada "RAISE" statement which raises some exception known only
within that block of code.

> 
> 	Richard Harter, SMDS Inc.

I am not associated with Ada in any way except as a former (and not
very thorough) student of it.  And as a potential user of it.  Ada
flames will not be appreciated if they only contain the SOT (Same Old
Thing).

				Lowell Savage, Boeing Aerospace Co.

Ada is a trademark of the Joint Ada Office of the DoD (I think).

My opinions will reflect those of my employer, my SA, or other entities
capable of "reflecting opinions" only if such entity pays me enough
to agree to release my opinions for such "reflection".