On 2017-05-03, at 12:30, Alan Altmark wrote:
> On Wednesday, 05/03/2017 at 03:47 GMT, Paul Gilmartin (π)
> <paulgboul...@aim.com> wrote:
>> Rexx's CALL instruction provides no way to indicate a null
>> last argument.
>
> CALL XYZ "fun", , "flags", ""
> XYZ: ARG p1, p2, p3, p4
>
> will provide a null string (length 0) to to both "p2" and "p4" the
> routine. You can get away without the trailing "" but only if the next
> line is empty. (Or...."How to make debug more challenging!")
>
> I have pretty much abandoned CALL in CMS in favor of function calls with
> null return values. The REXX interface to CMS (REXEXT macro) suppresses
> any null command, so I can get more creative in the way I call functions
>
This once caused me a problem. I had crafted a command environment to
which the null string was a meaningful command. But Rexx suppressed it.
I went to SR, and IBM fixed it (the Reference Manual made no exception
for the null string as a command.) But IBM said it remains suppressed
for ADDRESS CMS, ADDRESS COMMAND, and ADDRESS XEDIT.
> without resorting to syntax crutches like the ones above. It ensures that
> there is never ambiguity in the purpose of a trailing comma.
>
But, I can't provide an "OMITTED" final argument, no matter how
many commas or blank lines I supply. (Example not with IBM's
Rexx, but I believe it works the same:
/* Rexx *************** */ signal on novalue /*
null final argment?
*/
trace R
X = XYZ( "fun", , "flags", "", , , , )
call XYZ "fun", , "flags", "", , , ,
return( 0 )
XYZ: procedure
trace N
say arg()
do I = 1 to arg()
say I':' arg( I, 'E' ) arg( I ); end I
say
return( 0 )
/* ******************** */
6 *-* X = XYZ( "fun", , "flags", "", , , , )
11 *-* procedure
12 *-* trace N
4
1: 1 fun
2: 0
3: 1 flags
4: 1
7 *-* call XYZ "fun", , "flags", "", , ,
11 *-* XYZ:
*-* procedure
12 *-* trace N
4
1: 1 fun
2: 0
3: 1 flags
4: 1
9 *-* return( 0 )
-- gil
