Re: does modern Fortran have membership test similar to this Ada 2012 feature?

[Ron Shepard <ron-shepard@NOSPAM.comcast.net>]

In article <jrprpv$d6q$1@speranza.aioe.org>,
 "Nasser M. Abbasi" <nma@12000.org> wrote:

> In previous versions of Ada, membership tests allowed one
> to see whether a value was in a range or in a subtype, thus
> we could write either of
> 
>        if D in 1 .. 30 then
> 
>        if D in Days_In_Month then
> 
> but we could not write something like
> 
>           if D in 1 | 3 | 5 | 6 ..10 then
> 
> This is now rectified and following "in" we can now have one
> or more of a value, a range, or a subtype or any
> combination separated by vertical bars. Moreover, they do
> not have to be static.

This is basic functionality that is available in essentially every 
high level programming language.  However, the syntax is different.  
If D is a scalar, then the above would be done in fortran as

   if ( (D>=1) .and. D(<=30) ) then

If Days_In_Month is an array, then you could do

   if ( any(D==Days_in_Month) ) then


There are also lower-level constructs that could be used, including 
looping over the elements of Days_In_Month(:) and testing each one 
individually.  Sometimes that is actually the best approach, 
depending on what you need to do after the test.  In other cases, 
the best approach is something like

  if ( D==1 .or. D==3 ) then
     ...
  elseif ( D==2 ) then
     ...
  endif

or if the cases really are static you can do things like

  select case (D)
  case(1,3,5,6:10)
     ...
  case(2)
     ...
  end select case

The string of if-then-else tests requires effort proportional to the 
number of tests, so you generally want to order the most common 
cases first in the sequence.  The select case construct can be done 
by setting up a branch table, so the effort does not depend on the 
number of tests.

In fortran, the select-case construct requires static tests.  
However, in many situations you can map a set of dynamic comparisons 
to a fixed set of static cases, in which case you get the advantages 
of the branch table algorithm for your dynamic case.

$.02 -Ron Shepard