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SLIDES provides for the easy production of line drawings by the CORE
graphics system and <PLOT79>. It is driven by keyword commands on
input lines. Blank lines, unless they are part of a TEXT command, are
ignored. Leading white space (blanks or tabs) on command lines is
ignored. The command parsing is very similar to that available on
DEC-20 computers with the TOPS-20 operating system, and provides for
in-line comments, command continuation, multiple commands per line,
default values, command recognition, and in-line help. The major
difference at present is that the I/O is done entirely in FORTRAN; this
means that help and command recognition requests are not seen until a
carriage-return has been typed. However, command retyping will be done
using cursor-editing facilities of the interactive terminal to make it
visually the same or very similar to TOPS-20 command processing. While
a line is being entered, the usual terminal editing characters of the
host system are available. Additional editing characters are
available, however, and they may be listed and modified with the EDIT
command described in a later section.
Input is normally prompted for, although this may be suppressed with
the PROMPT command. The prompt strings change appropriately when a
multi-line command is entered as a reminder to the user.
In the command description following, parameters which are entered in
angle brackets (<parameter>) are optional. A vertical bar ('|')
indicates alternative keywords, one and only one of which must be
chosen. Parentheses are used for grouping lists, but are not part of
the command. Thus A|(B C) means the single value A or the pair of
values B C, while <A|(B C)> means A, or B C, or none of them.
Command keywords may be abbreviated to a few initial characters as long
as this preserves uniqueness. A minimum of 3 characters will usually
guarantee this, although there are a few exceptions. The MOVE, LINE,
ABSOLUTE, and RELATIVE keywords, because of their heavy use, may be
abbreviated to one letter. Letter case in keywords is not significant.
Tokens are lexical entities such as keywords, integer numbers,
floating-point numbers, switches, and quoted strings. They must be
separated by white space (blanks or tabs), and sequences of numeric
values may optionally also be separated by single commas.
Most commands require some graphical action to be taken, and a new plot
frame will be opened if one is not already open. The COLUMN, PAGE, and
SIZE commands cause any currently open plot frame to be closed, but
their specified action is delayed until a new frame is initiated.
An important facility of SLIDES is the ability to obtain the current
values of specified, or all, parameters at any time with the EDIT,
INQUIRE, and TERMINAL commands. Together with the default values
provided for most parameters, this makes it possible to easily find out
what can be left unspecified, and when something does not work
properly, what the parameter settings are which probably cause the
difficulty.