Hi Tony,
CLISTs also have the WRITENR statement, which Rexx lacks.
Regards,.
David
On 2025-01-09 16:49, Tony Harminc wrote:
On Wed, 8 Jan 2025 at 19:51, Lennie Bradshaw <lennie-brads...@outlook.com>
wrote:
CLIST design is over 50 years old I think.
CLISTs as we know them arrived with OS VS/2 Release 3, so the second
release of MVS around 1974 or so. Before that, on e.g MVT, SVS, and the
first MVS, CLISTs had no control flow statements - they were just lists of
commands with some substitution for arguments.
At introduction, everyone was all excited at the shiny new CLISTs, and I
remember well wondering why there was no lower case support, and if it
could be easily fixed. Indeed it could, and I found and happily zapped out
the upcasing and tried a CLIST with some lower case text in it. It blew up
all over the place, and I discovered that pretty much all byte values
beyond the upper case letters, numbers, and a few more (i.e. roughly the
JCL character set at the time) was being used as internal syntactic markers
for various aspects of the language. So much for that quick fix.
No, I don't remember the details, but I imagine much of today's CLIST
processor is unchanged from the 1970s version, and the source code for that
is available if anyone wants to research it further.
But seriously, why does anyone use CLISTs today? There is to my knowledge
just one reason: there is tight integration with TSO parsing and the CLIST
header, whereas REXX requires that the command be treated as a single
string, and then parsed with the (unarguably powerful) REXX parsing scheme.
But that doesn't allow for a syntax error to be discovered in the REXX and
the user prompted using TSO facilities; the REXX has to do all the work
itself.
Tony H.
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