ML/I User`s Manual
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1. are included in the listing 20 has an initial value of zero Y 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 Y 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 Y 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 4 ML I User s Manual Appendix Y Implementation on IBM PC under FreeBSD 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 12 if S12 ever goes negative t2. 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 The current source text line number is held in S2 it may be changed at any time 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 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 Count of processing errors 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 Not currently used Not currently used Not currently used Y 7 2 Use of 910 926 S10 Controls input selection a value of zero forces end of all input Values between 1 and 5 select the appropriate input stream values
3. ML TI User s Manual Appendix Y Implementation on IBM PC under FreeBSD R D Eager April 2006 This implementation is based on version CKN of ML T 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 http www ml1 org uk Y 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 runs on any version of FreeBSD ML T is a text based program so it runs from the command prompt Y 2 Operating instructions and I O The following options are accepted by ML I Upper and lower case option letters are ac cepted although only lower case ones are shown below v Print the version number of this implementation of ML T w n Set the amount of workspace available to ML I to n words the default is 5000 words 1l 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 f
4. ation 16 should be set to the ASCII code of the character to be translated and 17 to the ASCII code of the character that is to replace it For example if ASCII 37 was to represent a tab ASCII 9 16 and S17 should be set in the following way MCSET S16 MCSET S17 37 9 Initially 16 has the value 1 which since it does not correspond to a valid internal code will not cause any translations to be made Y 2 1 2 Ordering of input operations The ordering of input operations is as follows a Checking for 10 equal to zero b Checking for invalid values of 10 c Check for end of file if the revert stream is selected as a consequence of this check return to b d Translation using 16 and S17 e Checking for illegal characters Y 2 2 Control of output Output may be directed to any combination of the nominated output files including none at all The values of 21 and 22 control the selection 21 controls output to all four files and 22 controls output to the second file only this is just for backward compatibility Each bit in 21 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 o
5. between 101 and 105 cause the following actions to take place a 100 is subtracted from the value of 10 b the resulting value is stored back into 10 c the stream now specified by 10 is repositioned at its start S11 S12 S13 514 S15 S16 S17 S18 S19 S20 S21 S22 S23 S24 Values of S10 other than those given above apart from zero will cause an error The initial value of 10 is 1 Not currently used 12 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 12 by one If 12 ever becomes negative the process is aborted The user is at liberty to adjust the value of 12 at any time Not currently used Not currently used Not currently used Used to control character code translation Characters with the code given by 16 are translated to characters with the code given by 17 on input Initially 16 is 1 so no translations are performed See 16 above If bit 2 of 18 is nonzero at the end of a process a list is given of all currently defined constructions If bit 2 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 12 The current line number of the output text is held in 19 It may be changed if desired The value of 20 c
6. f 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 22 also causes output to file 2 to take place the presence of this value or the presence of the appropriate bit in 21 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 oper ating system 24 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 24 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 20 If 20 is zero no listing is produced at all If 20 is one a listing without line numbers is generated if S20 is two line numbers
7. he process is aborted 12 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 of S18 is nonzero It is preceded by a list of the currently defined constructions if bit 2 of S18 is nonzero 18 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 Y 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 Y 4 1 1 Too many lines to the debugging file Message Debugging file lines quota exhausted Description The value of 12 the quota of remaining lines allowed to the debugging file has become negative System Action The current process is aborted Y 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 23 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 Y 4 1 3 Input rewind failure Message Cannot rewind input stream Description ML I cannot reposit
8. ile 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 Y 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 10 2 Input is taken from the second input file given as an argument If this argument is omitted a fatal error will result when 10 is set to 2 10 3 Input is taken from the third input file given as argument If this argument is omitted a fatal error will result when 10 is set to 3 10 4 Input is taken from the fourth input file given as argument If this argument is omitted a fatal error will result when 10 is set to 4 10 5 Input is taken from the fifth input file given as argument If this argument is omitted a fatal error will result when 10 is set to 5 2 ML I User s Manual Appendix Y Implementation on IBM PC under FreeBSD If S10 is set to a value between 101 and 105 100 is subtracted from tha
9. ion the specified input stream following the setting of S10 to a value between 101 and 105 System Action The current process is aborted Y 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 Y 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 Y 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 6 ML I User s Manual Appendix Y Implementation on IBM PC under FreeBSD Y 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 10 to 24 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 10 which always cause the process to be terminated Y 7 1 Use of S1 S9 S1 S2 53 S4 S5 S6 S7 S8 S9
10. ontrols output to the listing file See Section Y 2 2 for details The value of 21 controls output see Section Y 2 2 for details Its initial value is 1 The value of 22 controls output to the second output stream only its use is deprecated See Section Y 2 2 for details Its initial value is 0 S23 contains the current revert stream See Section Y 2 1 for details 24 contains flags that indicate the status of each output stream see Section Y 2 2 for details
11. t value to obtain the number of the file to be selected for input the modified value is also stored back into 10 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 T treats this as end of file and ceases processing If 10 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 23 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 Y 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 transl
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