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Loadstar 17
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pattern matching
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2022-08-26
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╘HE ╨ERPLEXITIES OF ╨ATTERN ═ATCHING
BY
╩OSEPH ┴. ╟RAU
╔F YOU LIKE CONFUSION, YOU'LL LOVE
THE PATTERN MATCHING FEATURE OF THE
1541 ─╧╙. ┘OU KNOW WHAT ╔ MEAN -- THE
'*' YOU CAN USE IN ╠╧┴─ COMMANDS. ╔F
YOU USE THIS ALONG WITH PART OF A PRO-
GRAM NAME (AS IN ╠╧┴─'╨╥*' RATHER THAN
╠╧┴─ '╨╥╧╟╥┴═'), IT'S PRETTY STRAIGHT-
FORWARD. ┬UT WHAT ABOUT USING IT ALL
BY ITSELF, AS IN ╠╧┴─'*'? ╫HAT WILL
END UP IN YOUR ╥┴═ AFTER THAT COMMAND
EXECUTES? ╫ELL, LET'S SEE WHAT THE
EXPERTS HAVE TO SAY.
╞IRST WE CHECK THE ├OMMODORE 1541
─ISK ─RIVE ╒SER'S ╟UIDE THAT CAME WITH
THE DRIVE. ╔T SAYS THE 'LAST PROGRAM
ACCESSED ON THE DISK IS THE ONE
╠╧┴─ED. ╔F NO PROGRAM HAS YET BEEN
╠╧┴─ED, THE FIRST ONE LISTED IN THE
DIRECTORY IS THE ONE USED.' ╧╦, BUT
WHAT DOES 'ACCESSED' MEAN? ╘HE SECOND
SENTENCE MAKES IT SOUND LIKE '╠╧┴─ED'
AND 'ACCESSED' MEAN THE SAME THING --
BUT DO THEY?
╫ELL, THERE'S ALWAYS THE ├OMMODORE
64 ╨ROGRAMMER'S ╥EFERENCE ╟UIDE. ╔T'S
SURE TO HAVE THE ANSWERS. ╫ELL, NOT
THIS TIME. ╔T MERELY SAYS THAT '*'
╠╧┴─S 'THE FIRST FILE-NAME IN THE DISK
DIRECTORY.'
╫HEN ╔ GOT TIRED OF MUTTERING TO
MYSELF ABOUT THIS CONFUSION, ╔ DECIDED
TO DO SOME EXPERIMENTING. ╚ERE'S WHAT
╔ FOUND OUT:
(1) ┴FTER YOU POWER UP THE 1541
OR THE ├64 (OR BOTH), AND BEFORE ANY
PROGRAMS HAVE BEEN ╠╧┴─ED OR ╙┴╓┼D TO
THE DRIVE, ╠╧┴─'*' WILL ╠╧┴─ THE FIRST
PROGRAM LISTED IN THE DIRECTORY.
(2) ╔F YOU HAVE ╠╧┴─ED OR ╙┴╓┼D
ANY PROGRAMS SINCE POWER-UP, ╠╧┴─'*'
WILL ╠╧┴─ THE LAST PROGRAM YOU ╠╧┴─ED
OR ╙┴╓┼D.
┴ND THAT'S IT! ╘HERE ARE A FEW
POINTS YOU SHOULD NOTICE. ╘HE MANUAL
MEANS '╠╧┴─ED OR ╙┴╓┼D' WHEN IT SAYS
'ACCESSED.' ╙├╥┴╘├╚ AND ╥┼╬┴═┼ AREN'T
INCLUDED. ╬OTE, TOO, THAT TURNING THE
DRIVE OR THE COMPUTER OFF AND BACK ON
PUTS US BACK IN CONDITION (1). ┴ND
FINALLY, REMEMBER THAT, WHEN WE TALK
ABOUT ╙┴╓┼ AND ╠╧┴─, WE'RE TALKING IN
TERMS OF THE DRIVE -- NOT A PARTICULAR
DISK.
╙O WHAT? ╬ICE TO KNOW ALL THIS,
BUT IS IT OF ANY PRACTICAL VALUE? ├AN
WE PUT IT TO USE? ┘UP. ╘HIS INFORMA-
TION CAN BE USEFUL IN MAKING LIFE WITH
THE 1541 JUST A TAD EASIER AND IN
AVOIDING ONE OF THOSE NASTY ERROR
MESSAGES.
╞IRST WE'LL GET THE ERROR MESSAGE
OUT OF THE WAY -- LITERALLY. ╠ET'S
SAY YOU'VE BEEN WORKING AWAY AT YOUR
COMPUTER AND DECIDE TO RELAX WITH ONE
OF YOUR FAVORITE 'STORE-BOUGHT' GAMES.
┘OU ╙┴╓┼ THE PROGRAM YOU'RE WORKING ON
AND PUT THE GAME DISK IN THE DRIVE.
╬OW, AS THE LABEL ON THE GAME DISK
TELLS YOU, YOU ENTER ╠╧┴─'*',8,1. ╘HE
RESULT? ?╞╔╠┼ ╬╧╘ ╞╧╒╬─ ┼╥╥╧╥ ╫HY?
┬ECAUSE THE ├64 AND 1541 NEITHER KNOW
NOR CARE THAT YOU'VE SWITCHED DISKS,
AND ARE LOOKING FOR THE PROGRAM YOU
JUST ╙┴╓┼D. ╙OLUTION? ╘HE HANDY
ON-OFF SWITCH.
╬OW FOR A COUPLE OF TRICKS. ┘OU'RE
ALMOST FINISHED WITH YOUR MASTERPIECE:
THE PROGRAM-TO-END-ALL-PROGRAMS. ┴S
YOU'VE WORKED ON IT, YOU'VE ╙┴╓┼D EACH
NEW VERSION WITH A NUMBER TAG, THE
LAST VERSION BEING '╟┼═7'. ╬OW YOU
╙┴╓┼ '╟┼═8' AND PUTTER AROUND WITH A
COUPLE OF OTHER THINGS. ╘HEN YOU
RECALL YOU FORGOT TO ╙├╥┴╘├╚ '╟┼═7',
AND GO BACK AND DO IT. ┬UT LUCK AND
YOUR MEMORY BEING WHAT THEY ARE, YOU
END UP ╙├╥┴╘├╚ING '╟┼═8' -- THE LATEST
VERSION! ┴ND, OH YES, YOU ENTERED ╬┼╫
A MINUTE AGO. ╠OST '╟┼═8' FOREVER?
╬OPE. ╘RY ╠╧┴─'*', AND, AS LONG AS
YOU HAVEN'T ╠╧┴─ED OR ╙┴╓┼D ANYTHING
SINCE YOU ╙┴╓┼D '╟┼═8', THE PROGRAM
WILL ╠╧┴─ BACK JUST FINE, EVEN THOUGH
IT'S BEEN WIPED FROM THE DIRECTORY.
╬OW MY FAVORITE. ┘OU AND ╔ BOTH
KNOW THAT ╓┼╥╔╞┘ING A PROGRAM AFTER
YOU ╙┴╓┼ IT IS GOOD COMMON SENSE. ┬UT
MY PROBLEM IS THAT ╔'M ONE OF THE
LAZIEST PEOPLE ON ┼ARTH. ┴ND ╔ ALSO
TEND TO USE LONG, DESCRIPTIVE PROGRAM
NAMES. ╘HERE'S JUST NO WAY ╔'M GOING
TO TYPE SOMETHING LIKE
╓┼╥╔╞┘'╟╥┴─┼ ╙╘┴╘╙ ┬╧╧╘',8
AFTER EVERY ╙┴╓┼. ┬UT ╔ DON'T HAVE
TO. ╘HE BOOKS DON'T MENTION THIS, BUT
'*' WORKS JUST THE SAME WITH ╓┼╥╔╞┘ AS
IT DOES WITH ╠╧┴─. ╙O TO VERIFY ANY
PROGRAM IMMEDIATELY AFTER YOU'VE SAVED
IT, JUST USE '*'. ├OMBINE THIS WITH
THE ├64'S ABBREVIATION SCHEME, AND YOU
COME UP WITH THE UNIVERSAL ╓┼╥╔╞┘
STATEMENT -- ONE SHORT ENOUGH FOR EVEN
LAZY OLD ME TO USE:
╓[SHIFT]┼'*',8
┘OU MAY HAVE NOTICED THAT ╔'VE BEEN
DISCUSSING PATTERN MATCHING ONLY IN
TERMS OF A SINGLE 1541 DRIVE. ╚OW
DOES IT WORK WITH TWO DRIVES CHAINED
TOGETHER? ╧R A DUAL DRIVE? ┬EATS ME.
╔'VE ONLY GOT A SINGLE 1541. ╨ERHAPS
SOME OF YOU WITH DIFFERENT DRIVE
CONFIGURATIONS COULD DO SOME EXPERI-
MENTING OF YOUR OWN AND SHARE THE
RESULTS IN '╔NFLUX.'
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