Article-I.D.: dalcs.1497
Posted: Mon Apr 29 11:06:58 1985
Date-Received: Tue, 30-Apr-85 00:42:42 EDT
References: <370@sdchema.UUCP> <614@utcs.UUCP> <5318@tektronix.UUCP>
Organization: Dalhousie University, Halifax, N.S., Canada
Lines: 37

 >  	This is in response to the fact that statements like:
 >  
 >  	var = 'x' // var
 >  
 >  generally don't work as expected.
 >  
I have two comments.  First, when the discussion relates to f77
on Unix, I am never surprised when there is a failure to conform
to the standard, and therefore would not be surprised by anything
that f77 did to this statement.

But, of more relevance is what is supposed to happen within the
standard. As has been pointed out in another article, overlapping
string assignments are not permitted within the 1977 standard.

This question is however being considered by the Fortran Committee
of ANSI, namely X3J3, but in a much broader context. Fortran 8x
contains proposals for whole array operations and array sectioning.
There is also a statement that says roughly that in the event of
overlapping assignments (either for arrays or for strings or
substrings), the effect is that of evaluation of the right hand
side followed by assignment to the left. This is wonderful in prin-
ciple, but it does not take a lot of effort to figure out that
within subroutines this could have rather large implications, i.e.
either that the compiler write opts for execution efficiency and
ignores the possibility of overlap, or that he conform to the
standard, implements all operations using temporary arrays or
strings, and generates programs that grind along forever.

The Canadian Fortran Standards Committee has been following the
F8x proposals quite closely and has written to X3J3 and the Inter-
national Fortran Standards Committee (ISO/TC97/SC22/WG5) expressing
a number of concerns about proposals for F8x. Anyone wishing a 
copy of this report is welcome to one by sending me mail with a
UUCP or ARPANET address; I will respond with a copy in TeX source
form (which is reasonably readable without processing it with
TeX).