Copyright © 1985 R.D. Eager
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
1 to 4 as described in the supplements to that manual (startlines, stop
markers, controlled line numbers and optional warning markers). In
addition it contains a facility for suppressing the context print-out
following a message produced by a call of the operation macro
MCNOTE.
The following options are accepted by ML/I. Upper and lower case option letters are accepted, although only lower case ones are shown below.
-v
-w n-l file- is taken to mean the standard output.
-d file- is taken to mean the standard output.
-o file-o flag.
If no output files are specified, the standard output is used.
An output file named - is also taken to be the standard output.
All other arguments to ML/I are taken to be the names of input files;
there may be no more than five of these.
If no input file is specified, the standard input is used.
The name - is also taken to mean the standard input.
Input may be read from any one of the input streams; the value of S10
controls the selection. The possible values are:
S10 = 1
S10 = 2
S10 is set to 2.
S10 = 3
S10 is set to 3.
S10 = 4
S10 is set to 4.
S10 = 5
S10 is set to 5.
If S10 is set to zero, ML/I treats this as "end of file" and ceases
processing. If S10 is set to any illegal value (negative, greater than
five, or a value between one and five associated with an input stream
which has not been specified) then the process is aborted.
If a change of input stream is made, the original stream is not
"forgotten". Any attempt to read from this stream again will cause
ML/I to carry on where it left off.
When the end of an input stream is reached, ML/I checks to see if it is the
"revert stream". If it is, the process is terminated;
otherwise input is switched to the revert stream, and processing continues.
The revert stream is initially 1; its value is held in S23
and may be altered by the user if required.
There is no restriction on the length of an input line other than that imposed by the operating system.
It is possible to designate that one character be translated to another on input. This makes it possible to input a character that a device does not support. However, only one character code can be translated in this way.
If it is desired to perform a translation, S16 should be set to the
ASCII code of the character to be translated,
and S17 to the ASCII code of the character that is to
replace it. For example, if % (ASCII 37) was to represent a tab
(ASCII 9), S16 and S17 should be set in the
following way:
MCSET S16 = 37 MCSET S17 = 9
Initially, S16 has the value -1,
which since it does not correspond
to a valid internal code, will not cause any translations to be made.
The ordering of input operations is as follows:
S10 equal to zero.
S10.
S16 and S17.
Output may be directed to any combination of the nominated
output files, including none at all.
The values of S21 and S22 control the selection;
S21 controls output to the first file,
and S22 controls output to the second file.
If S21 is zero, output to the first file is suppressed;
if S21 is one, output to the first file is generated.
If S22 is zero, output to the second file is suppressed;
if S22 is one, output to the second file is generated.
Any attempt to send output to an output file not explicitly or implicitly specified on the command line is silently ignored.
There is no restriction on the length of an output line, save that imposed by the operating system.
A listing of the output from ML/I may be directed to the listing file
specified in the call of ML/I.
Listing is controlled by the value of S20.
If S20 is zero, no listing is produced at all.
If S20 is one, a listing without line numbers is generated;
if S20 is two, line numbers are included in the listing.
S20 has an initial value of zero.
ML/I uses a workspace area which is allocated at the start of the run.
Its size is controlled by the -w flag. The default is 5000 words.
The character set used by ML/I is 8-bit ASCII (codes from 0 to 255 decimal). Since all possible codes are used, the error character is never used.
Error messages are output to the debugging file specified in the call of ML/I; this defaults to standard error (usually the user's terminal). With reference to Chapter 6 of the ML/I User's Manual, the number 2N (the maximum number of characters inserted into an error message without truncation) is 64.
A count of processing errors (i.e. occurrences of the word
Error(s) on the debugging file) is maintained in S5.
At the end of a process, ML/I checks this value; if it is nonzero,
ML/I sets the shell "exit status" to 254, otherwise it is set to zero.
This allows shell files to detect the success (or otherwise)
of an ML/I process. Incidentally, an exit status of 255
is given if a fatal error caused ML/I to terminate the process prematurely.
An output lines limit is imposed on the debugging file, to curb excessive
output from a process that has gone badly wrong. The limit is implemented
by holding a quota of "lines left" in S12;
if S12 ever goes negative, the process is aborted.
S12 is initially 500, but may be changed by the user.
At the end of a process, a message of the form
At end of process: N lines, M calls
is output to the debugging file. If S18 is nonzero, this message
is preceded by a list of the currently defined constructions. S18
is initially set to zero.
All files are opened as soon as ML/I is entered. Failure to open any file causes an appropriate message to be output, and ML/I immediately exits.
The following run-time messages are peculiar to this implementation. They may be followed by other, advisory, messages which are self-explanatory.
Message
Debugging file lines quota exhausted
Description
The value of S12 (the quota of remaining lines allowed to the
debugging file) has become negative.
System Action
The current process is aborted.
Message
S10 has illegal value, viz n
Description
S10has been set to the value n, which is either outside the range 0-5, or is associated with an input stream that was not specified in the call of ML/I. Note that this error may be caused byS23(the revert stream) being set to an illegal value, and end of file then being reached on another input stream.
System Action
The current process is aborted.
Message
Error while writing to name file
Description
An error has occurred while writing to the file indicated by name.
System Action
The current process is aborted.
The initial environment contains ten permanent variables, all set to zero. All integers in, or derived from, macro expressions should be less than 32767 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 23 system variables. S1 to S9 are independent of the
implementation, and are used to control and monitor ML/I itself.
S10 to S23 are implementation dependent,
and are used to control input/output, etc.
If an S-variable is set to any value other than those given below,
the effect is undefined (except for invalid values of S10,
which always cause the process to be terminated).
S1-S9S1
S1 is one, the imaginary startline
character is inserted on input. If S1 is zero, no startlines are
inserted; this is the initial setting.
S2
S2; it may be changed at any time.
S3
S3 is one, the error message normally
generated if a warning marker is not followed by a macro name is
suppressed. If S3 is zero (the initial value), the message is
produced.
S4
S4 is one, the context print-out
normally given after a call of MCNOTE is suppressed. If
S4 is zero, the context print-out is given; this is the initial
setting.
S5
S6
S7
S8
S9
S10-S26S10
Values of S10 other than those given above (apart from zero)
will cause an error. The initial value of S10 is 1.
S11
S12
S12 contains the quota of lines on the debugging file. It is
initially 500, and every time ML/I outputs a line to the debugging file
(whether via an error message or a MCNOTE) it decreases
S12 by one. If S12 ever becomes negative, the process is
aborted. The user is at liberty to adjust the value of S12 at any
time.
S13
S14
S15
S16
S16 are translated to characters with the code given by
S17, on input. Initially S16 is -1, so no
translations are performed.
S17
S16 above.
S18
S18 is nonzero at the end of a process, a list is given of all
currently defined constructions.
The list isoutput to the debugging file (and is not subject to the quota
of lines imposed by S12).
S19
S19. It may
be changed if desired.
S20
S20 controls output to the listing file.
See Section N.2.2 for details.
S21
S21 controls output to the first output file;
a value of zero suppresses output, and a value of one allows it.
Its initial value is one.
S22
S21 controls output to the second output file;
a value of zero suppresses output, and a value of one allows it.
Its initial value is zero.
S23
S23 contains the current revert stream. See Section N.2.1 for
details.