13 Aug
2017
13 Aug
'17
11:55 p.m.
On 2017-08-13 19:24, Dave Horsfall <dave(a)horsfall.org> wrote:
Still there in FORTRAN 77.
The compiler recognize "GOTO I". And I have to be assigned to a
statement number (label). It has to be an integer variable, and when you
assign it to a label, you cannot do any arithmetic with it anymore. And
you assign it with a special statement. Thus, it can be used to store
what label to jump to, but you cannot use arithmetic to set what it
should jump to.
On Sat, 12 Aug 2017, Steve Johnson wrote:
Still there in FORTRAN 77.
A little Googling shows that the IF I mentioned
was called the
"arithmetic IF".
Ah yes. It was in FORTRAN II, as I recall. There was
also a Computed GOTO that branched to one of N labels
depending on the value of the expression.
I think that was still in FORTRAN IV?
And an
Assigned GOTO whose main use, as I remember, was to allow for
error recovery when a subroutine failed...
A real ugly statement; you assigned a
statement number to a variable, then
did a sort of indirect GOTO (or did the compiler recognise "GOTO I")? How those poor devils ever debugged their code with
such monstrous
constructions I'll never know.
It's actually not that hard. All this stuff is fairly simple to deal
with. The real horror in FORTRAN is EQUIVALENCE, which can give C a fair
fight for real horror stories.
But of course, bad programmers can mess things up beyond belief in any
language.
(And I never went beyond FORTRAN 77, so I don't know how current
versions look like. I stayed with PDP-11s (well, still do), and nothing
newer than FORTRAN 77 exists there. :-) )
Johnny
--
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|| on a psychedelic trip
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