4. Running the MCDS COSM AC Resident Editor (CRE)
21
of the pointer up to but not including the
-n+lst CR. If the pointer is in the middle of a
line, the last line (in this set of lines) will
consist of only those characters in the present
line to the left of the pointer. Thus, n=0
specifically indicates the portion of the
present line to the left of the pointer.
In certain cases a command mnemonic letter is
followed by one or two variable-length text arguments
(whenever the user needs to specify some sequence of
characters to insert or to search for). All such
arguments must be terminated by the ESC character
(echoed as $). In subsequent discussion, an arbitrary
text argument will be denoted by a symbolic statement
such as
“text”.
Correct Command
Typing Errors
A typing error in a command string may be
corrected by use of the RUBOUT (DEL) characterto
“erase” previous characters already typed. Do not use
backspace. Each time CRE receives a RUBOUT
within a command string, it erases the last character
from its stored version of the command string.
Further, it echoes back to the terminal the character
just erased. For example, suppose the user types the
command string ABC$DE (each of the letters is a valid
command mnemonic) followed by four rubouts. On
the terminal, he would see
ABC$DEED$C
where the last four characters were those erased. The
characters AB would then remain in CRE’s stored
command string register.
Clearly, any such erasures must occur before the
double ESC character, which terminates the command
string, is struck.
If CRE finds an invalid command while in execution
of a command string (i.e., after the user has typed the
double ESC), it returns to the user the error message
BAD COMMAND??“xxxx..xx$”
where xxx..xx reproduces that part of the command
string which has not been executed.
Interrupting CRE Execution
The user may at any time stop CRE execution by
depressing and holding the BREAK key on the
keyboard. This key is used, for example, to stop a long
typeout. On receipt of the BREAK, CRE stops
execution at whatever point was reached and returns
to the command input mode by issuing another
prompt. To assure the clean entry of succeeding
commands, the
RUBOUT
key should be depressed to
erase any erroneous noise characters that may have
been entered as a result of the break.
After a BREAK, the user should normally verify or
reinitialize the buffer pointer position before resuming
further editing.
Filled Work Space Warning
If CRE determines that a command stringthreatens
to use up the remaining work space, it will stop echoing
keyboard input characters to the printer and will echo
instead the BELL control character causing the I/O
data terminal to ring its bell as a warning. The user
should respond by erasing part of it with the RUBOUT
key.
If CRE runs out of space during command
execution, it will return the error message
MEMORY FULL “xxx...xx$”
where, again, xx...xx is a reproduction of the
unprocessed part of the command string.
CRE Commands
This section contains a summary of the individual
commands which CRE is designed to recognize. Each
command is described with a specification of its
acceptable format and an explanation ofitsexecution.
Single Commands
Pointer Control Commands
BEGINNING
Format: B
Execution: Pointer repositioned to the beginning of
the buffer.
END OF BUFFER
Format: Z
Execution: Pointer repositioned to the end of the
buffer.
CHARACTER STEP
Format: nC
Execution: Step pointer right (or left) by n characters.f
LINE STEP
Format: nL
Execution: Step pointer down (or up) by n lines
Reading the Input Tape
DEFINE READ TAPE
Format: R
Execution: After the command, CRE asks: READ?
The user enters 0 or 1, signifying appropriate tape,
followed by (CR).
fA positive (unsigned) n indicates the direction of right or down; a
negative n indicates left or up for all commands.
