From: corbett@lupa.eng.sun.com (Robert Corbett)
Newsgroups: comp.lang.basic.misc,comp.lang.c,comp.lang.cobol,comp.lang.fortran,
	comp.lang.pascal.borland
Subject: Re: Labels .. Pros and Cons
Date: 28 Apr 1999 03:14:17 GMT

In article <ueg15mw1t8.fsf@altair.dfrc.nasa.gov>,
Richard Maine  <maine@altair.dfrc.nasa.gov> wrote:
>Clive Page <cgp@nospam.le.ac.uk> writes:
>
>> I've read and enjoyed the "COME FROM" paper, and heard rumours of an actual
>> implementation: can you reveal the secret of who did it?
>
>It was implemented in the Elxsi Fortran compiler, sometime in the late
>'80s.  Bob Corbett was then working for Elxsi (he currently works for
>Sun and posts here occasionally).  I recall that Bob suggested,
>without saying what I'd find, that I use the debugger to peruse an
>area of the compiler executable.  Turned out to be an area with
>strings with the names of a lot of familliar-looking Fortran
>statements.  The string "comefrom" appeared there.
>
>I can verify first-hand that it worked because I wrote a trivial
>program to test it, making the obvious guess of its syntax and
>meaning.  It was, of course, undocumented, and I hadn't actually read
>the paper at the time.  Rumor has it that it was removed from the
>compiler after someone (not me) submitted a bug report about comefrom
>loops not optimizing as well as goto loops.
>
>--
>Richard Maine
>maine@altair.dfrc.nasa.gov

Yes, ELXSI Fortran implemented both the COME FROM and the conditional
COME FROM statement.  They were implemented by Ralph Merkle of trapdoor
knapsack and nanotech fame.  I don't recall that the COME FROM statement
was ever deleted, although ELXSI Fortran effectively has been.

					Sincerely,
					Bob Corbett