Copyright © 1972 R.C. Saunders
Permission is granted to copy and/or modify this document for private use only. Machine readable versions must not be placed on public web sites or FTP sites, or otherwise made generally accessible in an electronic form. Instead, please provide a link to the original document on the official ML/I web site.
This implementation of ML/I contains all the features described in the ML/I User's Manual, 4th Edition, August 1970, plus New Features as described in the supplements to that manual (startlines, stop markers, controlled line numbers and optional warning markers).
To run ML/I from the keyboard, the user types the following:
RUN ML1 | loads ML/I and enters it
|
|
|
KB:,KB:<KB: | results and messages to keyboard
|
| input from keyboard
| |
MCSKIP MT,<> |
|
MCDEF PIG AS DOG |
|
PIG |
|
| |
^C | end of file on keyboard is...
|
EN | ...EN carriage return linefeed
|
|
| |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
^C | ML/I asks for another command string
|
KI | To exit, type Ctrl-C KILL carriage return
|
RUN PIP | Load and run a new program
|
A typical command sequence to read a set of macros, the environment,
from a disk file LOWL.MCR and the source text from DECTape
file SOURCE.TXT on unit 1, and to send the value text to
DECTape file
VALUE.TXT on unit 0, and messages to the keyboard would be:
RUN ML1 |
|
ML1 V001 |
|
DT:VALUE.TXT,KB:<LOWL.MCR,DT1:SOURCE.TXT |
|
At the end of the process, ML/I asks for another command string. The
operator may reply: Ctrl-C, KILL, carriage return to
remove ML/I from core ready for the next program.
The usual conventions regarding command strings apply; note that in the following command:
#VALUE.TXT,KB:<KB:,SOURCE.TXT
input is taken from the keyboard, and because SOURCE.TXT is not
preceded by a device name, further input is taken from the keyboard by
default. To take input from disk, a DF: must be inserted before
the filename, unless it is the first file specification or the previous
file specification was from disk.
A maximum of four output file specifications may be requested:
e.g.
#DT:VALUE1.TXT,KB:,DT1:VALUE.LST,DF:VALUE2.TXT<SOURCE.TXT
If one of the file specifications is null, then that particular output
will not be generated. Output may be controlled during processing by
changing the values of S20-S22 as follows:
S20 = 0
S20 = 1
S21 = 0
S21 = 1
S22 = 0
S22 = 1
The initial values of these S-variables are set according to the contents of the command string.
A maximum of three input file specifications may be requested. Input is taken from the first file in the list until the end of file (see section H.2.4) is reached. A newline character is added if the last line was not terminated by a newline, and input is then taken from the succeeding files in the list, if any.
Spaces at the end of lines are always deleted.
The S-variables S11 and S12 can be set to restrict the
character positions within a line of input. This is most generally used
for card input to ignore the last eight columns (73 to 80), but it may
be used on any input device. ML/I ignores a character unless
S11 <= column number <= S12
where column number means "character position within line" for
files other than card decks. Initially S11 is 1 and S12 is
118, so that entire lines are read.
(note that if S12 is less than S11, then a newline is the
only character sent from that line, and ML/I will repeatedly input
newline characters until the end of source text.)
It is possible to arrange for one character to be translated into
another on input. Thus if a character is not available on a particular
device, for example a tab character on cards, S16 is set to the
internal code of the character to be translated, e.g. %, and
S17 is set to the code for tab.
Initially S16 is set to -1, so that no translations are
effected. The settings of S16 and S17 may be changed
dynamically if desired.
The input routine always deletes spaces from the ends of lines and then
translates using S16 and S17.
End of file for various input devices is designated as follows:
| a. | Fast paper tape reader | PR: | physical end of tape
|
| b. | Card reader | CR: | EOF card (see below)
|
| c. | Keyboard | KB: | ^C EN carriage return
|
| d. | Slow paper tape reader | PT: | ^C EN PT carriage return
|
An EOF card has 12-11-0 punched in column 1, but note that
at least one more card must be in the hopper after this to avoid a
hopper not ready (A002) message.
On return to command status, signified by #, the user has three
choices:
^C BE carriage return and the new command string.
Note that any MCALTERs from the previous processes will still be
active.
MCALTERs) by typing ^C KI carriage return followed by
RU or GE and the new program name.
The character set is that which is acceptable to DOS, i.e. the full ASCII character set including lower case letters and control characters.
Error messages are output to the message stream, the second dataset in the command string. The number 2N of Chapter 6 of the ML/I User's Manual is 60; thus if a piece of text in an error message is greater than 60 characters in length, the first 26 and last 26 characters are printed, separated by three dashes and some spaces.
The statistics message of Chapter 6 of the ML/I User's Manual is given at the end of every process.
The treatment of illegal input characters is compatible with other
DOS programs, e.g. PIP, EDIT. In practice,
parity is not checked on paper tape, and the error character, i.e. the
character which replaces illegal input characters, does not exist.
The following additional messages are output on the keyboard. In all cases the process is aborted, and an exit is made from ML/I.
Message
INPUT CHARACTER PARITY!
Description
A character was read which had odd parity.
Message
( INPUT) DEVICE PARITY! (OUTPUT)
Description
A hardware error was detected on a bulk storage device.
Message
( INPUT) INVALID LINE! (OUTPUT)
Description
On input, the maximum byte count was exceeded before a line terminator was found.
On output, the last byte was not a terminator (this message implies a software error).
Message
OUTPUT DEVICE FULL!
Description
An output device has no more free blocks.
The initial environment contains ten permanent variables. These are not preset to any particular values. All integers in, or derived from, macro expressions should be less than 32768 in magnitude. Overflow is not detected, except in the case of division by zero, and its effect is undefined.
The following are the layout keywords for this implementation:
SPACE | meaning a space
|
NL | meaning a newline
|
TAB | meaning a tab
|
SL | meaning the imaginary startline character
|
SPACES | meaning a sequence of one or more spaces
|
There are 24 S-variables available on the DOS PDP-11
implementation. S1 to S3 are described in the supplements
to the ML/I User's Manual. S10 to S24 are described
below:
| Input Controls | Initial value
| |
S10 | not used | 0
|
S11 | starting column | 1
|
S12 | terminating column | 118
|
S13-S15 | not used | 0
|
S16 | code to be translated on input | -1
|
S17 | code to replace S16 | 0
|
S18-S19 | not used | 0
|
| Output Controls | Initial value
| |
S20 | 0 do not list output | *
|
| 1 list output |
| |
S21 | 0 turn off output to results stream | *
|
| 1 turn on output to results stream |
| |
S22 | 0 turn off output to secondary results stream | *
|
| 1 turn on output to secondary results stream |
| |
S23-S24 | not used |
|
* means that these initial values reflect the command string used
for the current process.
This implementation of ML/I was supported by a Science Research Council grant to investigate the implementation of machine-independent software using the ML/I macro processor.