Path: utzoo!attcan!uunet!lll-winken!ncis.llnl.gov!helios.ee.lbl.gov!pasteur!ucbvax!UIAMVS.BITNET!AWCTTYPA
From: AWCTTYPA@UIAMVS.BITNET ("David A. Lyons")
Newsgroups: comp.sys.apple
Subject: CHR$(4), RETURNs, DOS3.3, BASIC.SYSTEm
Message-ID: <8901290132.aa16249@SMOKE.BRL.MIL>
Date: 29 Jan 89 07:24:59 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 48
X-Unparsable-Date: Saturday 28 Jan 89 10:06 PM CT

>Date:         Thu, 26 Jan 89 15:05:00 EST
>From:         "Kevin N. Gunn" <UNCKNG%UNC.BITNET@CUNYVM.CUNY.EDU>
>Subject:      Chr$(4) and Linefeeds
>
>I've come across this problem before (and fixed it by issuing a print
>chr$(4) twice, the first of which is, of course, terminated by a
>carraige return, thus solving the problem).  What I'd like to know is
>WHY DOS 3.3 NEEDS that carraige return.

The DOS 3.3 parser just watched characters as they were printed and
went into different modes depending on what it saw.  Seeing a
carriage return (Ctrl-M) made it go into a mode where a Ctrl-D would
make it go into collect-a-DOS-command mode.  I don't know of a really
good reason to require a return right before a command, except that
it lets you put Ctrl-D's into your files if you want, as long as they
aren't at the beginnings of lines.

BASIC.SYSTEM does things in a much more complicated way:  It turns
on TRACE mode and intercepts all the "#" signs and line numbers that
Applesoft prints; when it finds a "#" it checks the stack & zero
page to see what's going on, so it always knows what BASIC command
is being executed.  Things like TRACE and NOTRACE are handled
specially, and most importantly it remembers whether a PRINT is in
progress or not.  Under BASIC.SYSTEM a command is collected only if
the Ctrl-D was the first character printed by a PRINT statement.

By the way, just PRINT by itself prints a CHR$(13).  "PRINT" and
"PRINT CHR$(13);" are identical.  "PRINT CHR$(13)" (no semicolon)
prints _two_ returns.  So PRINT:PRINT CHR$(4);"xxxxx" is sufficient
to make sure DOS 3.3 sees a command.

>Carraige return sure is a strange anachronism when applied to a video
>screen, isn't it?
>
>-Kevin N. Gunn
>unckng@unc

Yes.  So are Line-feed (Ctrl-J) and formfeed (Ctrl-L) (nothing really
gets fed on the screen), and Bell (Ctrl-G) (there's no physical bell
in most equipment; just a speaker & an electronic noise of some
sort).  Shift keys no longer shift a tray of keys up or down to let a
different part of the metal hit the paper, either. Well, not on the
screen or most printers, anyway.

--David A. Lyons              bitnet: awcttypa@uiamvs
  DAL Systems                 CompuServe:  72177,3233
  P.O. Box 287                GEnie mail:    D.LYONS2
  North Liberty, IA 52317     AppleLinkPE: Dave Lyons