Copyright © 1986 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, 5th Edition, 1986, including New Features 1 to 6 as described in that manual.
The call of ML/I takes the form:
ML1/qualifier/qualifier... input1,input2,input3
The following qualifiers are recognised:
/PRIMARY_OUTPUT:fileSYS$OUTPUT is used for the primary output.
/SECONDARY_OUTPUT:file/LISTING_OUTPUT:file/DEBUGGING_FILE:fileSYS$ERROR is used.
/WORKSPACE_SIZE:n/VERBOSE
All qualifiers may be abbreviated as long as they remain unique
with respect to other qualifiers. Qualifiers may be separated
from their values by either a colon (:)
or an equals sign (=).
All output files must be different, and they must also be different from any of the input files. Any legal VAX/VMS filename may be specified for an output file.
Up to three input files (designated as input1, input2 and
input3 above) may be specified. If the first input
file is not specified, SYS$INPUT is used. An attempt to use an
input file (other than input1)
not specified in the call of ML/I will cause the
process to be aborted, after the output of a suitable message.
Any legal VAX/VMS character file may be specified as an input file, as long as the record size does not exceed 240 bytes and it is a CR format file.
$ ML1
This is sufficient for working through the Simple Introductory Guide.
PIG.TXT and DOG.MAR, and
output to FOO.DAT, with listing to BAZ.LIS:
$ ML1/PRI:FOO.DAT/LIS:BAZ.LIS PIG.TXT,DOG.MAR
Input may be taken from any one of the input files (or
streams, as they will be referred to from now on). The value
of S10 controls the selection. The possible values are:
S10 = 1
S10 = 2
S10 = 3
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 three, or a value between one and three 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 one; its value is held in S23 and
may be altered by the user if required.
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 (e.g. a vertical bar from certain DEC terminals). 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 either, both or neither of the primary
output and the secondary output. The values of S21 and S22
control the selection; S21 controls the primary output, and S22
controls the secondary output. In both cases, a value of zero means
that no output is to take place, and a value of one means that
output is to take place.
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.
The character set used by ML/I is 7-bit ASCII (codes from 0 to 127 decimal). However, character code 26 decimal (1A hexadecimal) is used internally to indicate end of file, and causes unpredictable effects if it appears in the input to ML/I.
Error messages are output to the debugging file specified in the call of
ML/I; this defaults to SYS$ERROR.
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. The error character is
question mark (?).
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 generates a standard VMS-style warning message if the
/VERBOSE qualifier was specified on the command line.
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 this value may be changed by the user
at any time.
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, followed (if S18 equals one)
by a list of the currently defined constructions.
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 0-3, 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
Primary output failure
Description
An error has occurred while writing to the primary output file.
System Action
The current process is aborted.
Message
Secondary output failure
Description
An error has occurred while writing to the secondary output file.
System Action
The current process is aborted.
Message
Listing output failure
Description
An error has occurred while writing to the listing file.
System Action
The current process is aborted.
Message
Debugging file output failure
Description
An error has occurred while writing to the debugging file. This message is output as a standard VMS-style message.
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 2147483647 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 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
S10 is one.
S11
SS$_NORMAL, but may be changed by the
user in order to pass back information to DCL.
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 one at the end of a process,
a list is given of all currently defined
constructions.
This is output to the debugging file (and is not subject
to the quota of lines imposed by S12).
If S18 is zero, the list is not produced.
The initial value of S18 is one.
S19
S19,
and is updated when the first character is output to each new line.
It may be changed if desired.
S20
S20 controls output to the listing file.
See Section S.2.4 for details.
S21
S21 controls output to the primary output stream,
and is initially set to one. See Section S.2.3 for details.
Its initial value is 1.
S22
S22 controls output to the secondary output stream,
and is initially set to zero. See Section S.2.3 for details.
S23
S23 contains the current revert stream, and is initially set to one.
See Section S.2.2 for details.
S24
S24 is initialised to the size of the workspace available to
ML/I (in bytes). It thus defaults to 5000 in the absence of the
/WORKSPACE_SIZE qualifier, and takes the specified value if that
qualifier is used. The contents of S24 are never subsequently
used or changed by ML/I; its sole purpose is to provide a means
whereby standard macro packages can check that sufficient space
is available before starting a potentially lengthy run that may
fail if not enough space is available. Of course, the amount of
space needed still needs to be determined in a previous run.