Pascal-FC Version 5 User Guide for PC Compatibles PC
Contents
1. ccsccccsssccssssccsssscesssscssssscsseees 4 Use of unsupported Options csccccssssssssssssssssescscssscsssescsssescssseessssssscseass APPENDIX C RUN TIME ERRORS u sccssscsssssssccssccsseccssscssccssscssssssseeseees EDeadlock goed case dadedcesscasiasdonscecesvesevandesensebsvatsssedesesovssvosebsndsdacseessssesbadsosdesopontsbiedes 2 A WAMME KE a E E T EET 3 Closed suar dS eneas assesi rones aaea sentence ciceecns sancee saan coe ees 4 Attempt to call entry of non existent terminated process cccscccssscsseees 5 Multiple activation Of a Process sccsssccssssscssssccssssccssssccsscsscssscssssssssssssseess 6 Division BY ZERO 65s ie resccosscisitessbcecesacepecacavesyscovecnecsninoaccencccsnentavdecteanscavedeavseccosseeee 7 Inv lid index ies cas cvossesaceseccnesciscesicasucangebiccsdncusncdbenedaaatoconncaegatiaaiseeesbeasanoacebante S Megal Character sccssecssstestedasecisstiececccaniecssvarcueseedasucistosderuss sdcesteussieeuariusessevsacenedc 9 Storad OV CLMOW sip cscsssscsisssaceessvencbs ede secvesseedees siscocecsieaveveadedsdescogues erissa is ees tose ods 10 Reading past end of file 5 c icccssesssssocssssonssaecsssesseceessstnscesvocassenuedecnseesanesveocaens 11 More than 20 processes sistssccticcaanseteisecesccsssnsscntadcasiactaavecsiasesseccedsssoanendeiascbiaads 12 Statement limit of 200000 reached possible livelock cscccsssscssseee 13 Label of not found in case istas2. E43 E44 E45 E46 E47 Pascal FC for PC Must not be var parameter The control variable of a for statement or replicate alternative may be a variable declared within the same block a variable declared in an enclosing block or a value parameter of the subprogram containing the for or replicate It must not however be a variable parameter of that subprogram Malformed entry call The compiler has interpreted a statement as an entry call but its form is incorrect As well as errors in statements which the programmer actually intended as entry calls this message will be generated if an attempt is made to activate a process anywhere outside the concurrent statement of the main program Not allowed in a process A language feature has been used that should not appear in a process declaration for example a nested process declaration This type must not be mapped It is illegal to use a mapping indicator with any condition object or any structured object which contains a semaphore object or a channel object Timeout terminate and else mutually exclusive More than one of these mutually exclusive alternatives has been used ina select statement Multiple cobegins Forward declarations s not resolved The declaration part of a block contains a forward declaration of a procedure or function for which no full declaration has been given This message is signalled at the end of the declaration part concerned Provides
3. any end end begin cobegin p coend end Pascal FC post mortem report on pmdtest5 Interpreter Version 5 1 Abnormal halt in process p with pc 21 Reason deadlock Main program Status awaiting process termination FC UG PC P P 3 1 3 14 Pascal FC for PC Process p Status active pe 21 Process suspended on chanarray 1 channel chanarray 2 channel chanarray 3 channel chanarray 4 channel chanarray 5 channel Global variables None FC UG PC P P 3 1 3 15 Pascal FC for PC APPENDIX A THE COMPILER LISTING FILE 1 Form of the listing file The contents of the listing file fall into the following sections 1 the source code listing itself 2 the symbol table generated from the program 3 the generated code Only the first of these sections will be of any interest to the majority of users Hence the symbol table and generated code have been omitted from the example in the following section 2 An example Pascal FC for IBM PC Compatibles Compiler Version 5 1 G L Davies amp A Burns University of Bradford Compiler listing for file gardensl pfc 1 0 program gardensl 2 0 3 0O first attempt to solve the 4 0 ornamental gardens problem 5 0 6 0 var 7 0 count integer 8 0 9 0 process turnstilel 10 0 Leh 0 var 12 0 loop integer 3 0 begin 14 0 for loop 1 to 20 do 15 4 count count 1 16 7 end turnstil
4. declaration s not resolved The provides construction has been used to predeclare the entries and possibly the parameters of a process or process type but a full declaration of the process or process type has not been given Variable expected Missing entry or entries declared in provides This error can be generated during the parsing of the full declaration of a process which has been pre declared in a provides construction Case label duplicated In a case statement two or more alternatives have the same case label Processes not allowed in record fields A process or array of processes has been declared as a field of a record Invalid set literal A bitset literal is a list of integer expressions enclosed in square brackets A set literal has been used that contains a value which is not an integer expression Variable is an array not a process When an array of processes has been declared each component process must be separately activated in the concurrent statement whole array activation is not permissible This error will result if insufficient subscripts are given when attempting to activate a process declared as an FC UG PC P P B 1 4 21 E48 E49 E50 E51 E52 E53 E54 E55 E56 E57 E58 3 2 Pascal FC for PC array element Error in array subscript declaration In the declaration of an array the type and range of each subscript is indicated by a constructions of the form lower high
5. lie in the range 0 7 17 Arithmetic overflow This error can result both from integer and real arithmetic operations when the result is too large or too negative to be represented It is also generated in two cases where an inappropriate argument has been passed to a standard function 1 anegative or zero argument to 1n 2 anegative argument to sqrt FC UG PC P P C 1 2 26 Pascal FC for PC 18 Attempt to initialise semaphore from process The main program thread including procedures and functions called by the main program to whatever depth is the only context in which the initial procedure can be called FC UG PC P P C 1 2 27 Pascal FC for PC APPENDIX D DISCLAIMER AND REPORTING OF FAULTS Though care has been taken to avoid faults in the Pascal FC implementations produced at Bradford the software is provided without any form of warranty and the authors cannot accept any liability arising from its use in any circumstances We wish to eliminate any hitherto undetected faults in any of our implementations Hence we invite users who discover faults to report them to Dr G L Davies Department of Computing University of Bradford Bradford West Yorkshire UK BD7 1DP email G L Davies bradford ac uk Please supply the following information 1 A listing of the Pascal FC source program any resulting Jistfile any resulting pmdfile output results where appropriate a short description of the pro
6. Pascal FC Version 5 User Guide for PC Compatibles PC PP G L Davies University of Bradford UK G L Davies 1992 Permission to copy without fee all or part of this document is granted provided that the copies are not made or distributed for direct commercial advantage Pascal FC for PC 1 INSTALLATION UNDER DOS It is recommended that Pascal FC be used on a system with a hard disc but use of a floppy disc system is feasible In either case the first task is to copy the distribution disc to a working disc and store the distribution disc in a safe place 1 1 Installation on a hard disc system A SETUP program is distributed with the system It will set up a directory structure for the Pascal FC system The procedure is as follows 1 Decide on the name and drive you want the Pascal FC system to be loaded into By default this is C PASFC but the SETUP program invites you to enter an alternative name if this is not suitable 2 Run the SETUP program Edit your AUTOEXEC BAT file to include PASFC BIN substituting your alternative name for PASFC if you did not select the default in the PATH variable If you successfully complete these steps you can run the Pascal FC system as described in Chapter 3 1 1 1 The SETUP program This program copies all the files you need to build a working system together with a selection of example programs The test programs are in a series of subdirectories of the directory EX w
7. blem ON ee nS an address preferably electronic mail where we can contact you FC UG PC P D 1 1 28 Pascal FC for PC CONTENTS 1 INSTALLATION UNDER DOS esseessoesessoesooescsssesoossosssessossocsseesossocssessossosssesss 1 1 Installation on a hard disc system c esoseoesosocessscocsssooccssosecessseosessoossssoo LAA The SETUP Program sosccessccsacsclscacccaiseseangaucitecsicenecseancevacanesseossivooceesansoe 2 OPTIONAL AND IMPLEMENTA TION DEPENDENT FEATURES 2 1 Data types supported 5 diese cds cectededccoatulsscesevecivoucsdacessenviddssecdasteoadeastonesdanuenche ZANTE type DME SOS LS iteiecscideiuctssascerddacedecsaseidacsestsuedtcvs descddaseisedavidisdsouduis 24 2 The type Char cia licecacl eecahistacciancanethiducnsodaaisoeuthineaudssn ccgucuautessusaassereniiee Bo VS VME LYE real isadestincshaseincdesseciaassceuecas dubcccalacesecbeoasdiaaipceuatassatcacaiacesnatenk 21 4 The type se SST fas scentudeceaicuctesacceuiaevevesdisseclalucissebeesscsousevevescuvatsdekesiene 2 2 Based literals oui docs tsscpncdcdaadecisdedssous lt basdedeseusssssess sdosdeucepestebs udodecssesentsveddesesesets 2 3 Based O tPp t cacessene cicisPetccacesselutiscasccaiavse caaiscacecaweddecanisuacsssadesecidancaceasesiueiaiies 2 4 B sed input ys ssceaicacasaiceiaseaiasdectancaciscensacdbedoescvasalesdactancasiictanescucadeacussalaesestecses 2 5 Processes and Process Scheduling ssesssecssocesooessocsssccssocesocesoosssocesseesso
8. ce Guarded procedures may only be declared in resources not monitors call not allowed within a resource An ordinary procedure call to a guarded procedure of a resource is only allowed from outside a resource Listing file diagnostics for these errors When any of the above errors are detected in a program the error diagnostics are sent to the listing file produced by the compiler and a rough indication of the location of the errors is also given in the listing of the source code In general the position at which the compiler finally concludes that an error has occurred is what is indicated and this is sometimes a little way beyond the actual site of the error possibly on a subsequent line The following example illustrates the form of the error diagnostics Note for example that error 9 has not been detected immediately This program has also generated a fatal error due to a typographical error in the final end FC UG PC P P B 1 4 22 Pascal FC for Compiler Version 5 1 G L Davies Compiler listing for file errorprone pfc 1 0 KOK KK KK KK 2 0 3 0 4 0 KOK KK KK KK 5 0 6 0 7 0 KOK KK KK KK 8 0 KOK KK KK KK 9 0 KOK KK KK KK 10 0 KOK RK RK KK TLE 0 12 0 ta 0 KOK OK RK KK 14 2 KOK KK KK KK 15 5 16 7 KOK OK RK OK ie 8 FC UG PC P P B 1 4 IBM PC COmpatibles Pascal FC for PC amp A Burns University of Bradford rogram errorprone 3S SesseS gt c
9. ch would have been executed had no error occurred 1 Deadlock The scheduler is unable to find an executable process and at least one of the processes in the program is suspended Chapter 3 of the Pascal FC Language Reference Manual discusses deadlock 2 Channel error Two or more receivers or two or more senders are attempting to rendezvous on the same channel Channels are for point to point communication between one receiver and one sender 3 Closed guards In the execution of a select statement all guards have evaluated to false and there isno else part 4 Attempt to call entry of non existent terminated process A call has been made on an entry of a process that was never activated or is now terminated 5 Multiple activation of a process An attempt has been made to activate several instances of a process in the concurrent statement 6 Division by zero This can result from real division or from integer division using the div and mod operators 7 Invalid index An array subscript is out of range 8 Illegal character The argument given to the chr function is outside the range 0 127 9 Storage overflow Memory space allocated for the main program or for a process has been exhausted This is likely to be caused by large data structures or by deeply nested subprogram calls FC UG PC P P C 1 2 25 Pascal FC for PC 10 Reading past end of file An attempt has been made to read when there are n
10. e call the standard and the unfair In either case the standard procedure priority has the same effect as the null statement 2 5 1 1 The standard scheduler The standard scheduler is pre emptive which means that a process can be forced to relinquish the processor even though it is still executable The scheduler selects a process to run by generating a random number In addition having determined which process to run it generates a random number which determines how many instructions the process will be allowed to execute before it is next forced out of the processor In practice this number is small so that process switches will occur frequently and no one process receives preferential treatment This scheduler is particularly useful for revealing errors due to uncontrolled multiple update 2 5 1 2 The unfair scheduler The unfair scheduler uses a different rule to select a ready process for running Rather than generating a random number it always chooses the lowest numbered executable process Processes are numbered in the order in which they were activated in the concurrent statement The unfair scheduler is not pre emptive once a process is running it will continue to do so until either it blocks or runs to completion 2 5 2 Maximum number of processes There is no specific limitation on the number of processes that can be declared in a program but no more than 20 may be activated in the concurrent statement An attempt to exc
11. e of optional Pascal FC facilities not supported by this implementation 2 Fatal errors Most of these errors are caused by overflow in one of the compiler s internal tables The two exceptions are program incomplete This message is generated when the compiler unexpectedly reaches the end of the program source file input line too long An internal line buffer limits the length of lines in the source program The limit was specified in Table 2 1 The remaining fatal errors which are all due to table overflow all produce messages which name the table involved The following notes provide additional information to assist in the interpretation of these messages 1 10 identifier The symbol table has overflowed This table is used to record all identifiers used in a program blocks Every subprogram monitor resource record type and entry declared in a program is recorded in the block table strings All string literals used in the source program are recorded in this table arrays Each new array type declared is recorded in this table This includes anonymous array types introduced in var declarations levels The degree of nesting of blocks or of record types is excessive code The source program has generated too much code channels This is analogous to the case for arrays Each new channel type declared in the program is recorded in the channels table select There are too many alternatives in a select stateme
12. e program has been executed Input redirection is also feasible but the response to the invitation to re run must be included with the input data if more than one run is required In preparing the data file the user should bear in mind that the interpreter code which manages the re run facility has the form repeat runprog writeln writeln Type r and RETURN to rerun if eoln then readln if eof then ch x else readin ch writeln nner not ch an EE ARIJ Hence the Pascal FC source program may or may not need an explicit readin to consume all the data prior to the re run response If the file is intended to contain only sufficient data for one run then the response to the prompt need not be included because the interpreter will detect the end of file condition and exit normally 3 3 The run time post mortem dump Pascal FC provides a post mortem dump when a program generates a run time error The dump is sent to a file with the name specified by pmdfile_name when the interpreter was called No file with this name is produced if the program terminates normally The post mortem dump is intended to be self explanatory and it will be introduced here by means of examples with a small number of supporting comments 3 3 1 Example accidental omission of a terminate alternative The following is an attempt at a buffered solution to the producer consumer problem using channels However there is no term
13. eed this number will cause the run time system to abort the program 2 6 Semaphores In the event that there are several processes suspended on a semaphore when a signal is carried out a random choice is made to determine which of them to unsuspend This is not affected by the scheduler in use 2 7 Monitors As there is no notion of process priority in this implementation all queues associated with monitors including those on condition variables are strictly FIFO This is not affected by the scheduler in use 2 8 Resources The implementation of resources has the following characteristics 1 Mutual exclusion at a resource boundary is implemented by a FIFO queue FC UG PC P P 2 1 3 4 Pascal FC for PC 2 Barriers on guarded procedures are FIFO queues If there are several processes suspended on true barriers which could inherit mutual exclusion of the resource a random choice is made to determine which is successful The above points apply regardless of which scheduler is used 2 9 Ada style rendezvous Process entries have FIFO queues which are not affected by the scheduler in use 2 10 Selective Waiting When there are several channel or accept alternatives which have open guards and pending calls a random choice is made among them except where the pri select is concerned In the latter case textual order determines the choice The scheduler has no influence on the choice of rendezvous 2 11 Timing Facilit
14. el T 10 18 10 FC UG PC P P A 1 3 16 Pascal FC for PC 19 10 process turnstile2 20 1 21 11 var 22 11 loop integer 23 11 begin 24 11 for loop 1 to 20 do 25 15 count count 1 26 18 end turnstile2 21 21 28 Zl 29 21 30 21 31 21 begin 32 22 count 0 3 3 25 cobegin 34 26 turnstilel 35 30 turnstile2 36 30 coend 37 35 writeln Total admitted count 38 39 end 2 1 Comments on the listing It will be seen that the compiler has pre pended two integers to each line of the original source code The first is clearly a line number The second is the instruction counter for the generated code and it represents the count as it was when the compiler began to process the line concerned This information is useful because the interpreters quote the instruction counter when they encounter a run time error so that the approximate location of the problem can be determined FC UG PC P P A 1 3 17 Pascal FC for PC APPENDIX B COMPILE TIME ERRORS 1 Types of error Error messages generated by the Pascal FC system fall into two categories 1 compile time errors 2 run time errors Run time errors are considered in Appendix C The compile time errors may be further divided into the following sub categories a fatal errors usually due to compiler internal table overflow b violations of the syntax of Pascal FC c us
15. er If the ordinal value of lower is in fact greater than that of higher this error is generated In addition there is a limit set on the ordinal value of both of these values Exceeding these limits also generates this error Constant expected No corresponding provides declaration In parsing the full declaration of a process which was pre declared using the provides construction an entry declaration has been found that was not included in the provides declaration Does not match provides declaration This error is associated with declarations of entries mapped to interrupt sources Either the entry concerned was mapped in the provides construction but not in the full declaration or vice versa or the integer identifying the interrupt source is not the same in the two cases Illegally nested accept An accept statement for a particular entry is nested inside an accept statement for the same entry accept not allowed in subprogram An accept statement is only allowed in the statement part of a process not allowed in a guarded procedure An attempt has been made to nest a guarded procedure declaration inside a guarded procedure declaration only allowed in a guarded procedure A requeue statement can only be placed in the statement part of a guarded procedure destination must be guarded procedure The destination of a requeue statement must be a guarded procedure in the current or some other resource only allowed in a resour
16. h pc 68 Reason deadlock See pmdfile for post mortem report Type r and RETURN to rerun The contents of pmdfile were as follows Pascal FC post mortem report on pcon6a Interpreter Version 5 1 Abnormal halt in process buffer with pc 68 Reason deadlock Main program Status awaiting process termination Process producer Status terminated FC UG PC P P 3 1 3 12 Pascal FC for PC Process consumer Status terminated Process buffer Status active pe 68 Process suspended on inp channel Global variables None Two points should be borne in mind when interpreting the post mortem dump 1 The approximate position in the Pascal FC source code where a process has been aborted can be found by using the program counter values printed in the associated listfile The value of pc given in the post mortem dump is the next instruction which would have been executed 2 Only non structured variables of types integer real char boolean and semaphore will be listed in the global variables section of the report 3 3 2 Example rendezvous that can never occur Finally here is a second example together with the post mortem dump produced program pmdtest5 const nchans 5 var chanarray array 1l nchans of channel of synchronous FC UG PC P P 3 1 3 13 Pascal FC for PC process p var loop integer begin select for loop 1 to nchans replicate chanarray loop
17. hich is itself a sub directory of PASFC Note that you can over ride the default name for the root of this structure PASFC but you have no control over the names of the sub directories To run the SETUP program enter A SETUP The program invites you to choose an alternative name for the root directory If the default name is suitable press ENTER In this case if a directory C PASFC already exists then you will be asked whether you wish to continue Entering y or Y will cause the existing C PASFC directory to be used Any files or directories with the same names as those on the distribution kit will be over written but others will be unaffected Pressing any other key causes the SETUP program to halt without copying any files A file A READ_ME will be found on the distribution disc this gives further information about the directory structure that will be set up FC UG PC P P 1 1 2 2 Pascal FC for PC 2 OPTIONAL AND IMPLEMENTA TION DEPENDENT FEATURES 2 1 Data types supported 2 1 1 The type integer Integers have 16 bits of precision The value of maxint is 32767 and the smallest integer that can be represented is maxint not maxint 1 2 1 2 The type char The ASCII character set is used Valid parameters to the chr function range from 0 to 127 2 1 3 The type real The standard type real is supported by this implementation Real numbers are represented with approximately 7 significant digits The approxima
18. ies The system clock unit is one second The clock function returns the time in seconds since the beginning of execution of the program The timing facilities in this implementation are designed on the assumption that only comparatively short program runs will be required The system clock will become negative if the program runs for more than about 9 hours and timings will become unreliable as this time approaches The timing facilities provide only approximate timings a process which executes the sleep procedure or a select with a timeout alternative may be made runnable up to one second early 2 12 Low level Facilities This implementation does not support mapping indicators in variable or entry declarations or offset indicators in record field declarations There is in consequence no facility to manipulate hardware device registers or to handle interrupts The type bitset is supported and has been described earlier 2 13 Restrictions imposed by compiler Internal Tables Table 2 1 lists the relevant restrictions Exceeding any of these limits except the number of significant characters in an identifier will result in a fatal error In the case of an identifier characters in excess of the limit are read but discarded FC UG PC P P 2 1 3 5 Pascal FC for PC Number of significant characters in an identifier 10 Maximum source line length characters 121 Size of identifier table entries 150 Size of block table ent
19. inate alternative in the buffer process FC UG PC P P 3 1 3 9 Pascal FC for PC program pcon6a buffered producer consumer with channel rendezvous var inp out channel of char process buffer const buffmax 4 var store array 0 buffmax of char nextin nextout count integer begin nextin 0 nextout 0 count 0 repeat select when count lt gt 0 gt out store nextout count count 1 nextout nextout 1 mod buffmax 1 or when count lt buffmax gt inp store nextin count count 1 nextin nextin 1 mod buffmax 1 end select forever end buffer FC UG PC P P 3 1 3 10 process producer var local char begin for local a to z do inp local end producer process consumer var local char begin repeat out local write local until local 2z writeln end consumer begin cobegin producer consumer buffer coend end When the program was run the following appeared on the screen FC UG PC P P 3 1 3 11 Pascal FC for PC Pascal FC for PC Pascal FC for IBM PC Compatibles Compiler Version 5 1 G L Davies amp A Burns University of Bradford Compiling pcon6a Compilation complete Interpreter Version 5 1 Program pcon6a execution begins abcdefghijkimnopgqrstuvwxyz Abnormal halt in process buffer wit
20. lation This is particularly useful if you want to investigate the influence of the scheduling policy on your program as the choice of scheduler is an option to the interpreter 3 1 1 The pfc command If you have the hard disc or 3 5 inch floppy disc system the pfc command can be used to compile and run the source program The command has the form pfc uf lt sourcefile_name gt No file name conventions are enforced by the compiler but it is recommended that you use a pfc extension The optional uf flag causes the unfair scheduler to be used in running the program the default is the standard scheduler 3 1 2 Running the compiler and interpreter separately To invoke the compiler a command of the following form is used pfccomp lt sourcefile_name gt lt listfile_name gt lt ob jfile _name gt Unless you want to save listings and compiler output from different programs it is best to use listfile and objfile respectively for the last two arguments However the ob jfile produced by the compiler is large so that it is not desirable to store programs in this form for long periods The code generated by the compiler is used as input to the Pascal FC interpreter Two versions of the interpreter are supplied they are identical except that one of them incorporates the standard scheduler and the other the unfair scheduler If there are no compile time errors the program may be run by typing the command pint lt objfile_name gt lt
21. nd modify only a local copy which would defeat their purpose for inter process communication Parameter list does not match previous declaration In an accept statement the formal parameters of the entry do not match exactly those given in the declaration of that entry Illegal character Unexpected symbol This error can be generated in many circumstances when the next lexical symbol in the source program is not what the compiler expects String expected Level error A language feature has been used at a static level which is inappropriate for that feature For example an inter process communication primitive has been declared elsewhere than in the declaration part of the main program Level 1 or an entry call has been made in the main program statement part Number error An error has been detected in an integer or real literal For example an integer literal is too large for the implementation Assignment not permitted The variable on the left of an assignment operator is an inter process communication type or is a structured object having such a type as a component exported monitor resource procedure s not declared One or more identifiers appeared in the export list of a monitor or resource for which no corresponding procedure declaration was found The message will appear following the final end of the offending monitor or resource FC UG PC P P B 1 4 20 E34 E35 E36 E37 E38 E39 E40 E41 E42
22. nt Note that a replicate alternative counts as a single alternative monprocs There are too many exported procedures in a monitor or resource reals Every unique real literal used in a program is entered into this table FC UG PC P P B 1 4 18 11 12 13 14 Pascal FC for PC interrupts Every semaphore channel or entry declared with a mapping indicator is entered into this table enum type Each new enumeration type declared requires an entry in this table This includes anonymous types introduced in var declarations case There are too many alternatives ina case statement monitors Too many monitors or resources have been declared in the program The values of the constants governing the sizes of the above tables will be found in Table 2 1 3 Non fatal Errors 3 1 List of messages Some of the error messages may require the brief explanations given below Others are self explanatory and have been simply listed for completeness EO El E2 E3 E4 E5 E6 E7 E8 E9 E10 Ell E12 E13 E14 E15 E16 E17 Undeclared identifier A reference has been made to an identifier which has not been declared or is not in scope Identifier duplicated An attempt has been made to declare an identifier which has already been declared in the current scope Identifier expected This error may be generated in numerous circumstances such as in constant type or variable declarations and in the formal pa
23. o more characters in the input file This message is relevant when input redirection is being used 11 More than 20 processes There is no specific limit on the number of processes that may be declared but this error will be generated if an attempt is made in a program to activate more than 20 12 Statement limit of 200000 reached possible livelock The run time system will abort the program if the statement limit is reached A common cause is livelock but it may simply be that the program s execution is too long 13 Label of not found in case The selector expression in a case statement has a value for which there is no corresponding alternative 14 Ordinal value out of range This can be generated during the execution of the pred and succ operators or during the semaphore initial procedure if a negative argument is given 15 Error in numeric input When executing a read an unexpected character has been found or a numeric value has been read which is out of range for this implementation or which uses a number base other than binary octal hexadecimal or decimal 16 Bitset value out of bounds There are three circumstances in which this error can occur 1 when using the bits type transfer function the integer argument supplied cannot be converted into a bitset without truncation 2 when using the in operator the left operand is not in the range 0 7 3 ina set literal the integer expressions do not all
24. ompiler and interpreter Separately ccscccsssceseees 3 2 Input and output redirection ccccscoccssssssssssssssssssssscsescscssscsssssssssosses 3 3 The run time post mortem dump scccccsssrcccssssrcccssesseccsssssecssssssseeees 3 3 1 Example accidental omission of a terminate alternative 3 3 2 Example rendezvous that Can never occur scccssssscccssssssccssessees contents CCeernrraranrntiuaunaunnsh Bh BB HP BR BP WW WWW WwW WwW WwW wWN NY NY pd ios Pascal FC for PC APPENDIX A THE COMPILER LISTING FILE o 0 ccsccssscssssessscssscceeceees 1 Form of the listing file cc iscscececdscesiccseseccsicenessoavcsstcoseeseeseavoaecevcecgvetoasdeoccsesenveneasee INIR CINE E T E TEAREN 2 1 Comments on the listing eesssesssesssecssocesocessosesocessecesocescossoocssseessocesocssooseso APPENDIX B COMPILE TIME ERRORS esseessessoescessescoesocsseecoesocsseesoesoesseee TP GSO error ssis scesdssccicsececcascocen va caseec sess oxcnoaveedgossosoncssaveae fugeaseveuaivontecaueouveesenee 2 Fatal err rS ieesscacccacancceakss caateaeeccdceansedocasesenasiasountesuecescennsoseccosnuosseassoueedeasodcesnase 3 N n fa atal Errors s ssssissecscssoscicssssroosesssooesosscsoeessssoos hoa dsonscbouassexssedeavsliseunsvoaaven vans JL List Of MESSA GOS 5 lt 2c055 lt a ccevcaneeseucsuscacenssaceevaacostencosyecevesnsecequsseeeces sdecdedeeaetvoresess 3 2 Listing file diagnostics for these errors
25. onst 1 1 o var x reel 0 i j integer EAT ch char 9 SAN begin ch 2 1 TB T ops egr he SOD T f 3 ebd 28 23 Pascal FC for PC Error diagnostics EQ undeclared identifier E2 identifier expected E3 type error E9 expected E13 program expected E27 illegal character E28 unexpected symbol FATAL ERROR program incomplete Following some kinds of error the compiler is unable to return immediately to the normal processing of input In these cases the input is ignored until normal processing has been resumed Sections of input ignored in this way are underlined as in Line 1 of the above example 4 Use of unsupported options Though this implementation does not support mapping indicators and offset indicators the compiler will still check the validity of the syntax of such features in the source program and report on any errors In addition a message will be given to warn that these facilities are not supported and the program will not be executable FC UG PC P P B 1 4 24 Pascal FC for PC APPENDIX C RUN TIME ERRORS In all cases the generation of a run time error results in the immediate termination of the program In most cases the approximate position where the error occurred is indicated by a message which indicates the value of the pc the generated code counter at the time the error occurred This counter points to the next instruction whi
26. pmdfile_name gt if the standard scheduler is required or ufpint lt objfile_name gt lt pmdfile_name gt for the unfair scheduler The pmdfile is used by the system to collect post mortem information in the event of a run time error see Section 3 3 The Pascal FC program may be re run any number of times without the need to restart the interpreter The following message will be displayed Type r and RETURN to rerun Woe Typing r or R will cause the program to run again any other character will terminate the interpreter Using the standard scheduler re running a program in this way will in general produce a different interleaving of processes Note that there may be some indeterminacy even when using the unfair scheduler because some scheduling decisions are still determined randomly for example when a signal is carried out on a semaphore on which several processes are blocked FC UG PC P P 3 1 3 8 Pascal FC for PC 3 2 Input and output redirection Input and output redirection are not available when using the pfc command Output produced by the source program is normally sent to the screen Normal MS DOS output redirection can be used when invoking the interpreter if a permanent copy of program output is required However redirection is not entirely satisfactory because any prompts for input from the source program will also be redirected to the named file So indeed will the invitation to Type r to rerun when th
27. rameter lists of subprograms Type error Generated in many circumstances where operands have invalid types expected expected expected expected men expected men expected expected expected expected program expected This is generated if the first line of the source file does not begin with program Comments excepted of expected then expected until or forever expected do expected FC UG PC P P B 1 4 19 E18 E19 E20 E21 E22 E23 E24 E25 E26 E27 E28 E29 E30 E31 E32 E33 Pascal FC for PC to expected begin expected end expected select expected export expected The first item in a monitor or resource declaration must be an export list replicate expected When using the replicator in the select statement for rendezvous by channel the replicate has been omitted do may have been erroneously used instead Error in parameter list A formal parameter list does not begin with an identifier or with var or the actual parameters in a subprogram call or entry call do not match the associated formals Must be var parameter Semaphore condition and channel objects may be passed as parameters to subprograms including processes but they must be formally declared as var parameters If they were permitted to be passed as value parameters then any operations carried out within the subprogram would access a
28. ries 30 Size of string table characters 1500 Size of array table entries 20 Maximum depth of nesting of blocks 7 Maximum length of generated code P code instructions 2000 Size of channel table entires 20 Maximum number of alternatives in a SELECT 20 Maximum exported procedures in a monitor or resource 10 Size of real literal table entires 50 Size of enumeration type table entires 20 Maximum number of alternatives in a CASE 20 Maximum number of monitors or resources in a program 10 Table 2 1 Compiler Internal Table Constraints FC UG PC P P 2 1 3 6 Pascal FC for PC 3 COMPILING AND RUNNING A PROGRAM 3 1 Invoking the Compiler under MS DOS The Pascal FC system consists of separate compiler and interpreter programs Figure 3 1 shows the system components and the files that they produce or use There are two ways of running a Pascal FC program using these components 1 by use of the pfc command which compiles and runs the source program by invoking the two components in turn 2 by running the compiler and interpreter separately The first of these methods is only available when the compiler and interpreter are on the same disc It involves less typing for the user but the second method has the advantage FC compiler source code FC interpreter Figure 3 1 Files and Pascal FC System Components FC UG PC P P 2 1 3 7 Pascal FC for PC that pre compiled programs can be run without re compi
29. se 2 5 1 Choice from among executable processes ssessscsssecssecssocesooesooeessesssee 2 5 1 1 The standard scheduler e eeesooossossssessseessoossoossosesssesssecssoosssosssssssse 2 5 1 2 The unfair scheduler sseosoesooesoesoesoossocssesooesosssessoesocssesssssosesessose 2 5 2 Maximum number of processes eesseoescsessocesoecssocesocescocessecssecesoossooseso 26 SemaPhoreS sca co css da cvssseecuteacocecucosvnechuedeceevasseusenk sdecececsseazerendsdacsesvencevtadstesweens A PA DNA KOS 1TA OI ESEE EEEE A A E A EE Ded RESOUECES cscciiscecavesacsecesscassecsestestess ccbcasebsececesaccesacsceseasessccbeassacsncescecssacseatestes 2 9 Ada style rendezvous siscscaesdececaciccteoasvissessevacanoucsdacdeatuciddsctcdelusacsecutoxesladuciens 2 10 Sel ctiye Waiting sisssssssorssssisesrsssdessssssssneoisstosescssdeodastssrssessddodoesions stosie sea 2 11 Timing Facilities 5 cisceccessdcoveataseas cosacepesgoavasysceuecvocsouseaeconnecpwencasencecsueneeeatie 2 12 Low level Facilities ssssssssssssestsssisossosessoissasoootsip oios soesbs seess ecos sesoses sosse ssis 2 13 Restrictions imposed by compiler Internal Tables sccsssscssssees 3 COMPILING AND RUNNING A PROGRAM esseessessoesoessessossoossessossoossesssse 3 1 Invoking the Compiler under MS DOS scsssccssssssssscccssscssscssseecees SEE THE pfe command iassccsstissesisceesccssccecsssssetecdsctorsesssusesescedessesssvesssscotesees 3 1 2 Running the c
30. sscesdeccnteitssiadsciascessitareccasseesososcesssdscdeddnssddesnecss 14 Ordinal value out of range esssessscsssccssccesocesoocesocessecssocesocesooeesocsssecssocssooseso 15 Error in numeric Nput sssssssiissossesssssesissasss osse iossscossssosess roissa sasise asas ssso tone 16 Bitset value out of bounds ssoesoessesoossoessessossosssessoesoossesoossocssessossosssesssssossse 17 Arithmetic overflow oiisissssscesustess sdeseccviiestsseadsonlacesvacabssdedonessavatcavdacsasdsssedvisdes 18 Attempt to initialise semaphore from process ssesssesssecssocesooessocessecssocesoceeo APPENDIX D DISCLAIMER AND REPORTING OF FAULTS 000 contents 16 16 16 17 18 18 18 19 19 22 24 25 25 25 25 25 25 25 25 25 25 26 26 26 26 26 26 26 26 27 28 Pascal FC for PC contents
31. te range of real numbers that can be represented is from 9 999999E37 to 9 999999E37 Any real number with an exponent more negative than 37 is considered zero 2 1 4 The type bitset These are sets of O 7 The write and writeln procedures use binary notation for values of this type with the most significant bit on the left The int function treats a bitset as an 8 bit unsigned integer and the bits function performs the inverse operation 2 2 Based literals The values for the base in a based literal are restricted to 2 8 and 16 The compiler will flag an error if any other value is used 2 3 Based output The values for the base ina write or writeln call are restricted to 8 and 16 Any other value will cause hexadecimal format to be used no error will be flagged Based output is not applicable to the type real nor can based output be used in conjunction with field width specifications 2 4 Based input Integers may be input in binary octal hexadecimal or decimal forms in response to read ln Decimal is the default and the format for the other bases is exactly the same as that required in a Pascal FC source program The format must not be specified in the source program input is interpreted appropriately at run time FC UG PC P P 2 1 3 3 Pascal FC for PC 2 5 Processes and Process Scheduling 2 5 1 Choice from among executable processes This implementation supports two different schedulers which w
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