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From: chris@mimsy.UUCP
Newsgroups: comp.lang.fortran
Subject: Re: Value parameters
Message-ID: <9132@mimsy.UUCP>
Date: Wed, 28-Oct-87 03:25:51 EST
Article-I.D.: mimsy.9132
Posted: Wed Oct 28 03:25:51 1987
Date-Received: Sat, 31-Oct-87 01:29:05 EST
References: <1331@cartan.Berkeley.EDU> <50500013@uxe.cso.uiuc.edu> <398@mn-at1.UUCP>
Organization: U of Maryland, Dept. of Computer Science, Coll. Pk., MD 20742
Lines: 34

In article <398@mn-at1.UUCP> alan@mn-at1.UUCP (Alan Klietz) writes:
><The problem that started all this, modifying a dummy argument corresponding
><to an expression, is detectable in the general case only with run-time
><checks, so Fortran 8x compilers will not be required to detect it.

>An expression is a constant syntactical entity, so it should be possible
>to detect the attempt at load time.

Not so.  Consider the following example:

  C I cannot stand all caps, so this is all lowercase
	subroutine sub(x, isexp)
	real x
	logical isexp

	real v

  C compute something based on x
	v = ...
	if (.not. isexp) then
  C reassign x
		x = v
	endif
	...
	end

A conformant program will then give `true' for `isexp' whenever
the value passed in as `x' is an expression, not a simple variable.

(It has been several years since I wrote any Fortran; apologies for
any bugs in the example above.)
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7690)
Domain:	chris@mimsy.umd.edu	Path:	uunet!mimsy!chris