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From: bernhold@qtp.ufl.edu (David E. Bernholdt)
Newsgroups: comp.lang.fortran
Subject: Interesting feature in Sun f77
Message-ID: <1250@orange19.qtp.ufl.edu>
Date: 25 Jan 91 20:59:01 GMT
Reply-To: bernhold@qtp.ufl.edu (David E. Bernholdt)
Organization: University of Florida Quantum Theory Project
Lines: 39


I've come across an interesting feature ;-) of Sun f77 v1.3.1.  There
is now a data type named BYTE, which is synonymous with LOGICAL*1.

BYTEs are allowed in some, but not all places integers are allowed.
They _can't_ be DO loop indices.  They _can_ be array subscripts.

Apparently due to BYTE and LOGICAL*1 being the same, it appears that
_any_ LOGICAL variable can now be an array subscript.  Not just things
which are specifically LOGICAL*1, but all possible LOGICALs (*2, *4,
and just plain)!

A side effect of this side effect is that typos such as
	If ( A(i .lt. j) )
instead of
	If ( A(i) .lt. j )
are taken without comment and give you completely bogus results.  My
sample type is pretty easy to spot, but any Fortran programmer can
probably imagine nice complex arguments where a misplaced parenthesis
is much harder to spot.

So...

1) Can anybody think of a way to get the compiler to help identify
typos such as my example above?

2) Can anyone with experience writing compilers say if it is realistic
to somehow expect that (for example) _only_ LOGICAL*1 be allowed as an
array subscript, while LOGICAL and *2 and *4 would give errors?

Basically, I want to know if I should consider this a bug which might
have a fix or workaround, or as an undesirable feature?

Thanks.
-- 
David Bernholdt			bernhold@qtp.ufl.edu
Quantum Theory Project		bernhold@ufpine.bitnet
University of Florida
Gainesville, FL  32611		904/392 6365