ML/I User's Manual --- Appendix AA --- Implementation on Apple under OS X


Node: Top, Next: , Up: (dir)

ML/I User's Manual -- Appendix AA

This implementation is based on version CKN of ML/I.

Copyright © 2006 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.


Node: Restrictions and Additions, Next: , Previous: Top, Up: Top

AA.1 Restrictions and Additions

This implementation of ML/I contains all the features described in the ML/I User's Manual, 6th Edition, February 2004. It is based on the source of the Linux implementation, and announces itself as such.

ML/I is a text based program, so it runs from the command prompt. It is provided as a 'fat' binary, and has been tested on an iMac and a G4 PowerBook.

Thanks to Ray Hutchings for compiling and testing this implementation.


Node: Operating instructions, Next: , Previous: Restrictions and Additions, Up: Top

AA.2 Operating instructions and I/O

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
Print the version number of this implementation of ML/I.
-w n
Set the amount of workspace available to ML/I to n words (the default is 5000 words).
-l file
Nominate file as the listing file. The default is that no listing is produced. The name - is taken to mean the standard output.
-d file
Nominate file as the debugging file. By default, this is the standard error stream (usually the user's terminal). The name - is taken to mean the standard output.
-o file
Nominate file as an output file. Up to four output files may be specified; each must be preceded by the -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.

AA.2.1 Control of 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
Input is taken from the first input file given as an argument. If there are no input files specified, input is taken from the standard input.
S10 = 2
Input is taken from the second input file given as an argument. If this argument is omitted, a fatal error will result when S10 is set to 2.
S10 = 3
Input is taken from the third input file given as argument. If this argument is omitted, a fatal error will result when S10 is set to 3.
S10 = 4
Input is taken from the fourth input file given as argument. If this argument is omitted, a fatal error will result when S10 is set to 4.
S10 = 5
Input is taken from the fifth input file given as argument. If this argument is omitted, a fatal error will result when S10 is set to 5.

If S10 is set to a value between 101 and 105, 100 is subtracted from that value to obtain the number of the file to be selected for input; the modified value is also stored back into S10. The difference between this and the use of values 1 to 5 is that the corresponding file is repositioned at its start; this is useful where a set of macros require multiple passes over a source file.

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.

AA.2.1.1 Input translation facility

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.

AA.2.1.2 Ordering of input operations

The ordering of input operations is as follows:

  1. Checking for S10 equal to zero.
  2. Checking for invalid values of S10.
  3. Check for end of file (if the revert stream is selected as a consequence of this check, return to b)).
  4. Translation using S16 and S17.
  5. Checking for illegal characters.

AA.2.2 Control of output

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 all four files, and S22 controls output to the second file only (this is just for backward compatibility). Each bit in S21 controls an output file; the least significant bit controls the first output file (as specified on the command line), the next bit controls the second output file, and so on. In each case, if the bit is set it indicates that output is to take place to the corresponding file. For example, a value of 1 would cause output to file 1; a value of 2 would cause output to file 2; a value of 4 would cause output to file 3, and a value of 3 would cause output to files 1 and 2. For backwards compatibility, a nonzero value in S22 also causes output to file 2 to take place; the presence of this value or the presence of the appropriate bit in S21 will cause output to take place, although the presence of both does not imply that output takes place twice.

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 any imposed by the operating system.

S24 contains a single bit flag for each of the output files; the least significant bit relates to the first output file (as specified on the command line), the next bit relates to the second output file, and so on. In each case, if the bit is set it indicates that the corresponding file is at the start of a line; this can be tested within macros and the information used to avoid generating unwanted blank lines. All output files not explicitly or implicitly specified on the command line are considered to be at the start of a line at all times. The effect of changing the value of S24 is undefined.

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.

AA.2.3 Workspace

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.


Node: Character set, Next: , Previous: Operating instructions, Up: Top

AA.3 Character set

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.


Node: Error handling, Next: , Previous: Character set, Up: Top

AA.4 Error handling

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 bit 2^1 of S18 is nonzero. It is preceded by a list of the currently defined constructions if bit 2^0 of S18 is nonzero. 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.

AA.4.1 Error messages

The following run-time messages are peculiar to this implementation. They may be followed by other, advisory, messages which are self-explanatory.

AA.4.1.1 Too many lines to the debugging file

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.

AA.4.1.2 Illegal input stream

Message

   S10 has illegal value, viz n
   

Description

S10 has 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 by S23 (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.

AA.4.1.3 Input rewind failure

Message

   Cannot rewind input stream
   

Description

ML/I cannot reposition the specified input stream, following the setting of S10 to a value between 101 and 105.

System Action

The current process is aborted.

AA.4.1.4 Error on writing to output file

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.


Node: Integer calculations, Next: , Previous: Error handling, Up: Top

AA.5 Integer calculations

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.


Node: Layout keywords, Next: , Previous: Integer calculations, Up: Top

AA.6 Layout keywords

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.


Node: S-variables, Previous: Layout keywords, Up: Top

AA.7 S-variables

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 S24 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).

AA.7.1 Use of S1-S9

S1
If 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
The current source text line number is held in S2; it may be changed at any time.
S3
If 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
If 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
Count of processing errors.
S6
If the value of S6 corresponds to the ASCII code for a valid character, then that character is treated as if it were a letter for the purposes of constructing atoms. This means that it is possible to have a single, specified, non-alphanumeric character as part of an atom. The initial value of S6 is -1, so this feature is disabled by default. Note that it is the value of S6 at the time the character is scanned that is important, so it is not possible to define macros containing different characters defined by S6; at scan time only the one containing the character corresponding to the current value of S6 would be handled correctly.
S7
Not currently used.
S8
Not currently used.
S9
Not currently used.

AA.7.2 Use of S10-S26

S10
Controls input selection; a value of zero forces end of all input. Values between 1 and 5 select the appropriate input stream; values between 101 and 105 cause the following actions to take place:
  1. 100 is subtracted from the value of S10;
  2. the resulting value is stored back into S10;
  3. the stream now specified by S10 is repositioned at its start.

Values of S10 other than those given above (apart from zero) will cause an error. The initial value of S10 is 1.

S11
Not currently used.
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
Not currently used.
S14
Not currently used.
S15
Not currently used.
S16
Used to control character code translation. Characters with the code given by S16 are translated to characters with the code given by S17, on input. Initially S16 is -1, so no translations are performed.
S17
See S16 above.
S18
If bit 2^0 of S18 is nonzero at the end of a process, a list is given of all currently defined constructions. If bit 2^1 of S18 is nonzero at the end of a process, processing statistics are given. Both of these items are output to the debugging file (and are not subject to the quota of lines imposed by S12).
S19
The current line number of the output text is held in S19. It may be changed if desired.
S20
The value of S20 controls output to the listing file. See Section AA.2.2 for details.
S21
The value of S21 controls output; see Section AA.2.2 for details. Its initial value is 1.
S22
The value of S22 controls output to the second output stream only; its use is deprecated. See Section AA.2.2 for details. Its initial value is 0.
S23
S23 contains the current revert stream. See Section AA.2.1 for details.
S24
S24 contains flags that indicate the status of each output stream; see Section AA.2.2 for details.