4. Running the M CDS COSM AC Resident Editor (CRE)
25
ENTER
Fig. 7—Execution of nested composite
command.
To execute a nested command, CRE maintains a
stack in part of the available work space. The amount
of stack space required depends on the depth of nesting
in the command, i.e., on the number of loops within
loops, as in Fig. 7, which in turn depends on the depth
of bracket-pairs-within-bracket-pairs in the command
string. If CRE runs out of stack space during
execution, it will issue the error message:
ITERATION STACK FAULT
This error message is most likely to occur if the
brackets in the command string are not paired
properly. In particular, it occurs if a bracket is missing.
Note that if the user fails to terminate a
text
string
with the required ESC character, all subsequent
characters until an ESC does occur will be treated as
part of the presumed
text
string. Thus, it is quite
possible that a missing ESC in a nested command
string could also result in the “improperly-paired-
brackets” errors message, ITERATION STACK
FAULT.
Horizontal Tabs
CRE assumes an implicit horizontal tab stop after
every eight character positions in a line. If the user
types a HORIZ TAB character (CONTROL and I) as
part of a TEXT field, CRE will insert this character
into its buffer, but it will echo back to the printer a
sufficient number of spaces to reach the next implied
tab stop. HORIZ TAB characters read from the input
file are loaded into the buffer as is. On output, each
HORIZ TAB buffer character is converted into the
required number of spaces, extending the line length in
the process. Thus, HORIZ TAB characters cannot
appear on the output tape. The TAB character can be
used to produce straight columns in a source file.
Note:
As a special case, CRE interprets a text
beginning with a HORIZ TAB character as if an
INSERT command had preceded it.
Additional Note
Normally, the INSERT of a non-existent text field
(i.e., the command 1$) results in no operation. Further,
it is normally illegal to precede an INSERT command
with a numeric argument. However, the specific
command nI$ (combining the two) is legal. It causes
the insertion of a single character whose ASCII
decimal value is n (module 128).
For example, 101$ will cause insertion of a LF
character (hex 0A).
Using CRE
In this section, information is given on the
development and manipulation of a file through use of
the Editor (CRE). In addition, some useful common
sequences are given to illu strate C R E ’s data
manipulation facilities.
Creating a File
A file is created by a repeated sequence of the
following steps:
(1) File buffer from keyboard with sequence of
INSERT’s.
(2) WRITE buffer to output file.
A single I command may take as an argument a text
string of arbitrary length. Thus, many lines may be
inserted with a single I command. Each line is
terminated by pressing the CR key. A typical INSERT
will thus appear on the printer as
—> I
line 1
. .Insert command and 1st line of
. .text.
line 2
. .Additional lines
. .Additional lines
. .Additional lines
