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From: alan@mn-at1.UUCP (Alan Klietz)
Newsgroups: comp.lang.fortran
Subject: Re: Value parameters
Message-ID: <398@mn-at1.UUCP>
Date: Sun, 25-Oct-87 18:14:48 EST
Article-I.D.: mn-at1.398
Posted: Sun Oct 25 18:14:48 1987
Date-Received: Wed, 28-Oct-87 02:02:49 EST
References: <1331@cartan.Berkeley.EDU> <50500013@uxe.cso.uiuc.edu>
Reply-To: alan@mn-at1.UUCP (0000-Alan Klietz)
Organization: Minnesota Supercomputer Center
Lines: 62

In article <50500013@uxe.cso.uiuc.edu> hirchert@uxe.cso.uiuc.edu writes:
<
<Instead of legal programs or compilers, people should be talking about
<standard-conforming programs or compilers, but I don't think anyone is mislead
<by this short cut in vocabulary.  The real point is that the standard places
<only minimal requirements on compilers.  The primary requirement is that it
<correctly handle standard-conforming programs.  There is no requirement that it
<detect programs that do not conform and there probably never will be.

Not a requirement?  But desirable.  A compiler that purports to offer
standardization and portability features must offer an option to issue
warnings about the use of non-standard constructs.

<In other words, the Fortran standard is designed
<to support a fast language, not necessarily a safe one.  The restrictions in
<it are designed not for enforceability, but to provide the compiler with the
<information it needs to efficiently optimize the code it produces.

Although not required, a good compiler should offer an option to detect
"unsafe" constructs, even at a loss of runtime speed during the prototype
design phase.

<
<While reserved words maginally improve error interpretation, they can cause
<severe portability problems, especially when the addition of extended features
<results in the addition of new reserved words.  For toy languages supporting
<mostly student programmers who are expected to commit many errors and not
<understand them, reserved words are fine, but for programs millions of lines
<long with lifetimes measured in decades, they can be a severe problem (unless,
<of course, you have the kind of clout DoD had in demanding that there would
<be no extended Ada's).

Fortran has no reserved words.

<
<Fortran 77 has structured selection (i.e., the block-IF) but no structured
<looping because the committee that produced it was able to reach a quick
<consensus on the former but not the latter.  The proposed draft for Fortran 8x
<does include a structured loop (albeit somewhat different from those offered
<by WATFOR77), as well as data structures, recursion, internal procedures,
<dynamic storage allocation, and many other features people seem to expect in a
<"modern" language. 

About time.  After what, 30 years?

<(By the way, the draft of Fortran 8x does include a 
<requirement that standard-conforming compilers have an option to detect the
<syntactic violations of the standard)

Ah, so it's a requirement after all.  Good.

<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.

<
<Kurt W. Hirchert

-Alan Klietz