Path: utzoo!mnetor!uunet!husc6!linus!necntc!ima!haddock!karl
From: karl@haddock.ISC.COM (Karl Heuer)
Newsgroups: comp.lang.c
Subject: Re: The D Programming Language: cases
Message-ID: <3120@haddock.ISC.COM>
Date: 22 Mar 88 23:11:19 GMT
References: <25200@cca.CCA.COM> <3278@okstate.UUCP> <336@wsccs.UUCP>
Reply-To: karl@haddock.ima.isc.com (Karl Heuer)
Organization: Interactive Systems, Boston
Lines: 28

In article <336@wsccs.UUCP> terry@wsccs.UUCP (terry) writes:
>I think that [an explicit fallthrough statement] would be dangerous, in that
>it would have further reaching effects than Richard anticipates.  Since the
>discussion centers around 'D', which by context is simply "a new standard C
>which may not be compatable with the current K&R standard of C so we'll call
>it 'D'", I believe that "upward" compatability must be maintained if all C
>software is to be recompiled in D with minimal tweaking.

That sounds more like a description of ANSI C.  "D" is intended to be a
language which is as powerful as C but (unlike ANSI C and C++) is *not bound
at all* by the compatibility requirement.  (Although a C-to-D translation tool
would probably appear, in the unlikely event that this thought experiment
actually materializes into something tangible.)

>While a change this drastic _could_ be worked around with something as simple
>as    #define case fallthrough; case    this does _not_ help code generators
>such as YACC and LEX generate this new code.

What's the problem?  I think yacc currently generates a break after each case
block; the solution then is to omit this if generating D.  Even if yacc does
depend on the current automatic fall-through semantics, it could generate an
explicit "fallthrough;" statement at the bottom of each case block.  Surely it
has enough information for this -- I'd bet it's a one-line change.

(Btw, although I would prefer a "fallthrough" statement to the current C
semantics, I think that both are inferior to "goto case N".)

Karl W. Z. Heuer (ima!haddock!karl or karl@haddock.isc.com), The Walking Lint