\documentstyle[a4,12pt]{article} \begin{document} \author{APM Manual pages} \title{APM IMP Compiler -- Version 2} \maketitle \parskip .1 in \setcounter{secnumdepth}{10} \parindent 0in \section{Preamble} The IMP compiler translates programs written in the high-level language IMP to M68000 native code. The operation of the compiler is very similar to the APM Pascal compiler -- for example, the available options are identical. \section{ALERT information} {\hspace*{0.3 in}} . This information relates to the Version 2 Compiler {\hspace{0.2 in}} ("NIMP") \\ {\hspace*{0.5 in}} Modules compiled with this compiler are incompatible with \\ {\hspace*{0.5 in}} (ie cannot be linked with) modules compiled by the V1 compiler. {\hspace*{0.3 in}} . The checking of unassigned variables and nil references is not \\ {\hspace*{0.5 in}} 100 per cent. \section{Calling the compiler} {\hspace*{1.7 in}} Example commands \small\tt \begin{verbatim} IMP MYPROG Compile MYPROG with default options producing object file MYPROG.MOB IMP PARSER-LIST Compile PARSER producing object file PARSER.MOB and listing file PARSER.LIS IMP NEW.IMP-NOCHECK-NODIAG Compile NEW.IMP to NEW.MOB without checks and diagnostic hooks IMP PROG2-NOEDIT Compile PROG2 to PROG2.MOB without calling the editor to correct faults detected in the program \end{verbatim}\rm \normalsize \subsection{Parameters} There is only one obligatory parameter for the IMP command and that is the name of the IMP source program to be compiled. There is no default file-name extension for the source file-name. As a matter of personal preference, programmers may or may not choose to adopt the extension .IMP for IMP programs. There are two output files which may be generated by the Compiler: the object file containing the compiled code and the listing file. By default, the names for these files are derived from the source file-name. The default names may be overridden by specifying alternative names, either positionally or by keyword. For example, the generation of an object file may be suppressed in either of the following forms: {\hspace*{0.7 in}} IMP PROG2/:N \\ {\hspace*{0.3 in}} or {\hspace{0.3 in}} IMP PROG2-OFILE=:N Similarly a listing could be directed to a designated file by: {\hspace*{0.7 in}} IMP MYPROG/,PUB:TEMP {\hspace{0.6 in}} \{note the comma \\ {\hspace*{0.3 in}} or {\hspace{0.3 in}} IMP MYPROG-LFILE=PUB:TEMP \subsection{Object file} By default, the Compiler generates an object file provided that no errors are detected during compilation. If no name is provided explicitly, the name is derived from the source file-name (without the extension .IMP if present). The extension .MOB (for Motorola object) is applied to the object file-name. The compiled code file is eligible for execution by citing the name (without extension) as a command verb at APM command level. There is no linking stage after compilation; the object file is immediately executable. For example: {\hspace*{0.3 in}} \} IMP MYPROG \\ {\hspace*{0.3 in}} MYPROG compiled: 115 statements (+ 38 comments) to 1220 bytes (+ 24) \\ {\hspace*{0.3 in}} \} MYPROG \subsubsection{Object file control} \small\tt \begin{verbatim} -OFILE= produce object file with specified name (the extension .MOB is added unless present already) -OFILE=:N do not produce object file -FORCE produce object file even if program faulty \end{verbatim}\rm \normalsize \subsection{Listing file} By default the Compiler does not produce a listing. If one is required, it is requested either by including the keyword -LIST in the command or by specifying a file-name as the second output parameter or as the value for the keyword -LFILE. If no name is provided explicitly, the name is derived from the source file-name (without the extension .IMP if present). The extension .LIS is applied to the listing file-name. The listing file consists of the text of the source file with added line numbers, and any fault or warning messages produced during compilation. Line numbering runs from 1 at the start of the file and includes blank lines and comment lines. Lines in included files are numbered independently, with an ampersand as an indicator. \subsubsection{Listing control} \small\tt \begin{verbatim} -LIST produce source file listing -LFILE= send listing to specified file (the extension .LIS is added unless already present) -TT send listing to terminal -MAP output information at end of each procedure, indicating size of code, etc. -LOG print statistics at end of compilation indicating number of statements, atoms per statement, identifiers per statement, time taken, etc. \end{verbatim}\rm \normalsize \{The following may not be available in the standard release\} \small\tt \begin{verbatim} -CODE print hybrid assembly language interpretation of code generated for each statement. This is before address fix-up and branch shortening, and so does not fully reflect the final code -DICT print dictionary entries for identifiers \end{verbatim}\rm \normalsize \subsection{Options} Run-time checks: To disable any individual check, use the indicated keyword prefixed by NO, for example -NOSTRASS \small\tt \begin{verbatim} -ASS include unassigned check on full integers -STRASS include unassigned check on strings -SASS include unassigned check on 16-bit values -BASS include unassigned check on 8-bit values \end{verbatim}\rm \normalsize Defaults: -ASS -STRASS -NOSASS -NOBASS The unassigned check is implemented by standardising all newly declared dynamic variables to a fixed pattern which is an improbable integer value. The check is defaulted off for variables occupying less than 32 bits because there is a greater possibility of the special pattern occurring as a genuine value. Note that almost all examples of the violations listed below which involve only literal operands are detected and rejected at compile-time rather than run-time. \small\tt \begin{verbatim} -ARR include array bound checking -OVER include overflow check on addition/subtraction -CAP include capacity checking on assignment -STACK include stack over-run check Defaults: -ARR -CAP -STACK -NOCHECK suppress all checks apart from stack over-run -NOCHECK-NOSTACK suppress all checks \end{verbatim}\rm \normalsize Run-time diagnostic control: \small\tt \begin{verbatim} -LINE include line-number updating for diagnostics -TRACE generate code which allows the program to be executed one line at a time under the control of the Software Front Panel \end{verbatim}\rm \normalsize Default: -LINE -NOTRACE Compiler limits: \small\tt \begin{verbatim} -IDENTS=n allow for n user idents (default 1000) (also controls the total lengths allowed for) -KBYTES=n allow for codesize nK (default 64k, max 128k) \end{verbatim}\rm \normalsize Compile-time control: \small\tt \begin{verbatim} -NONS enable warning-free use of non-standard features -STRICT exclude use of non-standard features -LOW enable use of low-level features -VOL assume functions and for-loop increments and end-values are volatile -WARN request soft warnings -EDIT automatically transfer control to the standard editor (VECCE) on detection of an error in the program. Compilation resumes when the edit is closed (just hit CPY if you do not want to correct the error at this stage). \end{verbatim}\rm \normalsize Default: -NONONS -NOSTRICT -NOLOW -VOL -WARN -EDIT \section{Language facilities} The IMP language as implemented on the APM is substantially the same as the Vax/VMS version as defined in the EUCSD Report "The IMP77 Language" (3rd Edition). Differences and special options are described in the following sections. \subsection{Exclusions} {\hspace*{0.2 in}} . {\hspace{0.2 in}} full diagnostics and \%monitor are not yet available {\hspace*{0.2 in}} . {\hspace{0.2 in}} \%string(*)\%array\%name variables are not implemented {\hspace*{0.2 in}} . {\hspace{0.2 in}} procedures and functions passed as parameters must be in scope to the \\ {\hspace*{0.5 in}} procedure to which they are passed {\hspace*{0.2 in}} . {\hspace{0.2 in}} there is no built-in function TYPEOF {\hspace*{0.2 in}} . {\hspace{0.2 in}} untyped \%name parameters are usable only to supply an address, not type \\ {\hspace*{0.5 in}} or length information; the built-in function SIZEOF is not applicable to \\ {\hspace*{0.5 in}} such parameters {\hspace*{0.2 in}} . {\hspace{0.2 in}} \%name \%function as variant for \%map is not accepted {\hspace*{0.2 in}} . {\hspace{0.2 in}} \%on \%event * is not permitted as a way of trapping all events {\hspace*{0.2 in}} . {\hspace{0.2 in}} line-breaks after \%and and \%or are not ignored {\hspace*{0.2 in}} . {\hspace{0.2 in}} non-decimal constants expressed in IBM style (X'...') are accepted, but \\ {\hspace*{0.5 in}} with a Non-standard warning {\hspace*{0.2 in}} . {\hspace{0.2 in}} the Atlas Autocode style of \%for loop (without \%for) is accepted, but \\ {\hspace*{0.5 in}} with a Non-standard warning {\hspace*{0.2 in}} . {\hspace{0.2 in}} loops with a control clause after as well as before (ie an \%until as well \\ {\hspace*{0.5 in}} as a \%while or \%for) are accepted, but with a Non-standard warning \subsection{Modified features} {\hspace*{0.2 in}} . {\hspace{0.2 in}} the effect of \%continue is to pass control to the head of the containing \\ {\hspace*{0.5 in}} loop, where any \%while or \%for control clause is tested; any \%until \\ {\hspace*{0.5 in}} clause at the end of the loop is ignored. {\hspace*{0.2 in}} . {\hspace{0.2 in}} if no initial value is specified for an own variable, this means that it \\ {\hspace*{0.5 in}} is initially unassigned, NOT zero. \\ {\hspace*{0.2 in}} . {\hspace{0.2 in}} the preferred way of initialising \%name variables of all kinds is in the \\ {\hspace*{0.5 in}} form "==NIL". The earlier form "==0" is also accepted, with a warning. {\hspace*{0.2 in}} . {\hspace{0.2 in}} event 9 is used exclusively for end-of-input; file system errors are \\ {\hspace*{0.5 in}} signalled as event 3, and non-numeric input for READ as event 4. {\hspace*{0.2 in}} . {\hspace{0.2 in}} the Compiler is stricter about the ordering of statements than the Vax \\ {\hspace*{0.5 in}} IMP Compiler. The normal ordering in any block should be declarations, \\ {\hspace*{0.5 in}} then event trap if any, then instructions. It is acceptable for static \\ {\hspace*{0.5 in}} declarations (eg procedures and \%own variable declarations) to be \\ {\hspace*{0.5 in}} interspersed among instructions, but the Compiler queries any dynamic \\ {\hspace*{0.5 in}} variable declarations which appear after instructions, and hard-faults \\ {\hspace*{0.5 in}} any which appear in a loop or after a sequence change. {\hspace*{0.2 in}} . {\hspace{0.2 in}} In the declaration of an array name variable, as in {\hspace*{1.0 in}} \%INTEGER \%ARRAY \%NAME A(lo1:hi1,...,loN:hiN) {\hspace*{0.5 in}} each of the lower and upper bounds may be: {\hspace*{0.5 in}} (a) a literal or literal expression, for example: {\hspace*{0.7 in}} \%integer\%array\%name a(1:1000) \\ {\hspace*{0.7 in}} \%real\%array\%name delta(10:20,1:30) {\hspace*{0.7 in}} In this case, the corresponding bound of every actual \\ {\hspace*{0.7 in}} parameter must have the identical literal value. {\hspace*{0.5 in}} (b) a variable declaration, for example: {\hspace*{0.7 in}} \%byte\%array\%name used(1:\%integer xdim,1:\%integer ydim) \\ {\hspace*{0.7 in}} \%short\%array\%name count(\%byte lo:\%byte hi) {\hspace*{0.7 in}} In this case, the corresponding bound of the actual parameter is \\ {\hspace*{0.7 in}} assigned to the stated variable at the time of procedure entry. This \\ {\hspace*{0.7 in}} case, which is similar to the Pascal conformant array concept, is \\ {\hspace*{0.7 in}} confined to \%array \%names as procedure parameters. It cannot be used \\ {\hspace*{0.7 in}} for \%array \%names declared as ordinary variables. {\hspace*{0.5 in}} (c) an asterisk, for example: {\hspace*{0.7 in}} \%integer\%array\%name cases(1:*) {\hspace*{0.7 in}} The use of an asterisk should be confined to the UPPER bound of the \\ {\hspace*{0.7 in}} FIRST (outer) dimension only, and when it appears, all other bounds \\ {\hspace*{0.7 in}} should be literal. It implies an unspecified number of elements in \\ {\hspace*{0.7 in}} the array (and the absence of bound-checking even with checks on). {\hspace*{0.5 in}} For the time being, the Vax/VMS form ... \%array(n)\%name ... is also \\ {\hspace*{0.5 in}} accepted, but note that the '(n)' part is obligatory even when n is one. \subsection{New warning messages} Warnings are issued in a number of cases where it may be useful to have an indication of possible hazards at compile-time rather than run-time. {\hspace*{0.2 in}} . {\hspace{0.2 in}} All unused switch index values are reported \\ {\hspace*{0.5 in}} [add a switch label with index (*) to eliminate] {\hspace*{0.2 in}} . {\hspace{0.2 in}} A report is made if the destination variable(s) in a string resolution \\ {\hspace*{0.5 in}} are not manifestly capacious enough to receive whatever might be assigned \\ {\hspace*{0.5 in}} to them. \\ {\hspace*{0.5 in}} [increase the length (to 255 if necessary) to eliminate] \subsection{Data types} \small\tt \begin{verbatim}%integer range: -2147483648 (-2^31) to 2147483647 (2^31 - 1) storage: 32 bits %long%integer not accepted %short range: -32768 to 32767 storage: 16 bits %half range: 0 to 65535 storage: 16 bits %byte range: 0 to 255 storage: 8 bits %mite range: -128 to 127 storage: 8 bits %real reals are limited to single-precision (32-bits) and the implementation is by software %long%real treated as %real, apart from type-checking %record, %array, %string -- standard \end{verbatim}\rm \normalsize \subsection{\%OPTION} Compiler options are generally established at the outset in the command used to call the compiler. However, most of them may also be switched off and on within the program text by means of the directive \small\tt \begin{verbatim} %OPTION "...." for example %OPTION "-NOWARN-NOLIST" \end{verbatim}\rm \normalsize The quoted string must consist of a sequence of Option keywords each preceded by a dash (hyphen). {\hspace*{0.3 in}} Caution: indiscriminate variation of checking options within a \\ {\hspace*{0.9 in}} program can create considerable confusion for debugging. The effect of options is localised to the current procedure or block. \subsection{\%INCLUDE} Other files may be included in the source by means of the directive \small\tt \begin{verbatim} %INCLUDE "...." for example %INCLUDE "GRAPHICS.IMP-NOCHECK" \end{verbatim}\rm \normalsize The quoted string specifies the name of the file together with any Options to be applied to it. These Options, and any which are specified within the included file itself, are localised to this file. Include files may be nested to a maximum of three. \subsection{Record initialisation} A record type identifier may be used as a constructor for that record type, from components values specified in parentheses following the record type identifier. At present only literal component values are permitted. This form is particularly useful for specifying initial values for records, but it is not restricted to that context. The component values may be presented either positionally or using the record component names, preceded by the sub character ('\_'), as keywords. \subsubsection{Examples of use of record constructors} \small\tt \begin{verbatim}%record%format f1(%integer lo,hi, %string(7) code, %byte%name where, %short weight) %own%record(f1) r1=0 {Meaning: numeric values = 0, strings = "", names == NIL} %own%record(f1) r2=f1(-100,100,"FACTOR",nil,1) %own%record(f1) r3=f1(0,,"DUMMY") {By enumeration, any omitted values unassigned} %own%record(f1) r4=f1(_code="UNDEF",_weight=99) %own%record(f1) r5=f1(_hi=99999,_code="MAX") {By selection using field names, any omitted values unassigned} { field names must appear in order of occurrence in declaration} \end{verbatim}\rm \normalsize \subsection{Declaration attributes} The keyword \%volatile may be prefixed to a function declaration to indicate that the result of the function is not a pure function of its arguments. This stops the compiler optimising repeated calls. The prefix '@'$<$machine-address$>$ may be placed in front of a variable or procedure declaration to indicate that the corresponding entity is to be addressed at the location indicated. The $<$machine-address$>$ may be either an absolute value or a register-relative value. For example: \small\tt \begin{verbatim} @16_041234 %byte DEVICE STATUS @16_1BC8 %routine ABANDON (formally equivalent to an %external %spec) @4(A5) %integer USERNO \end{verbatim}\rm \normalsize Caution: this is a Low-level facility \subsection{Name-relative addressing} When a number of elements of a given type are stored consecutively, for example, in an array or mapped file, it is sometimes convenient to use a \%name variable as a base point for addressing different elements. The name-relative addressing facility allows this to be done. This takes the form of a \%name variable followed by an index value enclosed in square brackets. Such an expression denotes a reference to the variable located that number of elements away from the element identified by the current assignment to the name variable. Caution: this is a Low-level facility There is no check on the validity of the references. Use of the facility is, however, preferable to the use of store-mapping functions in a similar role, because it preserves the type identity of the objects denoted. \subsubsection{Example} With the following definitions and assignment: \small\tt \begin{verbatim} %recordformat PAIR(%real x,y) %record(pair)%array A(1:100) %record(pair)%name P P == A(7) \end{verbatim}\rm \normalsize the following would hold: \small\tt \begin{verbatim} P[2] would denote A(9) P[-6] would denote A(1) P == P[1] would advance P to denote A(8) \end{verbatim}\rm \normalsize \section{Standard libraries} \subsection{Pre-declared procedures} The procedures listed below are available without specification. \small\tt \begin{verbatim}%integer%map INTEGER(%integer a) %real%map REAL(%integer a) %string(*)%map STRING(%integer a) %record(*)%map RECORD(%integer a) %byte%map BYTEINTEGER(%integer a) %short%map SHORTINTEGER(%integer a) %byte%map LENGTH(%string(*)%name s) %byte%map CHARNO(%string(*)%name s, %integer n) %integer%fn ADDR(%name n) %string(1)%fn TOSTRING(%integer k) %string(255)%fn SUBSTRING(%string(255) s, %integer from,to) %integer%fn REM(%integer a,b) %integer%fn INTPT(%real x) %integer%fn INT(%real x) %real%fn FRACPT(%real x) %real%fn SQRT(%real x) %integer%fn CPUTIME !in milliseconds (since process creation) %name NIL %record%format EVENTFM(%byte event,sub, %short line, %integer extra, %string(255) message,%integerarray r(0:15)) !LINE and R are APM-specific extensions %record(eventfm) EVENT %const%integer NL %const%string SNL %integer%fn NEXTSYMBOL %routine READSYMBOL(%name n) %routine PRINTSYMBOL(%integer k) %routine SKIPSYMBOL %routine PRINTSTRING(%string(255) s) %routine READ(%name n) %routine WRITE(%integer m, n) %routine PRINT(%real x, %integer n,m) %routine PRINTFL(%real x, %integer n) %routine NEWLINE %routine NEWLINES(%integer i) %routine SPACE %routine SPACES(%integer i) %routine SELECT INPUT(%integer n) %routine SELECT OUTPUT(%integer n) %routine CLOSE INPUT %routine CLOSE OUTPUT %routine SET INPUT(%integer pos) !establish new active position for current input stream ! set input(0) resets to the beginning of a file !!! temporary restriction: only POS=0 accepted *** %routine SET OUTPUT(%integer pos) !establish new active position for current output stream ! set output(0) resets to the beginning of a file !!! temporary restriction: only POS=0 accepted *** %routine RESET INPUT {equivalent to SET INPUT(0) %routine RESET OUTPUT {equivalent to SET OUTPUT(0) %integer%fn INSTREAM %integer%fn OUTSTREAM %routine OPEN INPUT(%integer n, %string(255) S) !*selects N at present* %routine OPEN OUTPUT(%integer n, %string(255) S) !*selects N at present* %string(255) CLIPARAM ! returns the parameter string supplied with the command ! invoking the program %routine PROMPT(%string(255) S) \end{verbatim}\rm \normalsize \subsection{General-purpose Libraries} There are a number of libraries available on the system which provide groups of related procedures for use in writing programs. In order to make use of these, it is necessary to include the necessary declarations in the source program. Also, when running the program, it may be necessary to INSTALL the related object file (see the general system information on Libraries). Short files containing the relevant declarations for the main system libraries are available for general use in the directory INC. These files may be 'included' in IMP programs by means of the \%INCLUDE statement, for example, \%INCLUDE 'INC:UTIL.IMP'. Library interface files currently available are: {\hspace*{0.3 in}} INC:UTIL.IMP -- sundry utility procedures \\ {\hspace*{0.3 in}} INC:FS.IMP {\hspace{0.3 in}} -- file system procedures {\hspace*{0.3 in}} [others under preparation] \subsubsection{Example of use of UTIL} \small\tt \begin{verbatim} {Simple file copy program} %begin %include "INC:UTIL.IMP" %string(255) inname,outname %on %event 9 %start; !end-of-file %stop %finish define param("Input file:",inname,PamNodefault+PamInfile) define param("Output file:",outname,PamNewGroup+PamNoDefault+PamOutfile) process parameters(cliparam) print line("Copying ".inname." to ".outname) select input(1); select output(1) %cycle read symbol(ch); print symbol(ch) %repeat %endofprogram \end{verbatim}\rm \normalsize \subsection{External linkage} The pre-prepared libraries make use of the general external linkage mechanism implemented for IMP. This allows external REFERENCES in one program to be matched up with external DEFINITIONS in another program or module. The linkage takes place automatically when the program is run. In IMP, an external reference starts with the keyword \%external and includes the keyword \%spec after the type. For example: {\hspace*{0.3 in}} \%external \%routine \%spec INITIALISE(\%integer case) \\ {\hspace*{0.3 in}} \%external \%integer \%spec CURRENT DEVICE In APM IMP, external references must appear at the outermost textual level, that is, before the first \%begin or in the main program block. An external spec for a procedure may be satisfied by a procedure occurring later in the same module, but the same is not true for variables. External definitions start with the keyword \%external. For example: {\hspace*{0.3 in}} \%external \%routine INITIALISE(\%integer case) \\ {\hspace*{0.5 in}} ...... \\ {\hspace*{0.3 in}} \%end {\hspace*{0.3 in}} \%external \%integer CURRENT DEVICE=2 These must appear in the source file before the main block (if any). A program module containing external procedures or variables, and terminated by \%endoffile, is compiled in the ordinary way, eg IMP MYLIB. Before the externals it contains can be accessed, the compiled module must be installed by the INSTALL command. The INSTALL command takes as parameter the name of a program file (extension MOB assumed) -- or list of names separated by commas. For example INSTALL MYLIB. The effect of installing a program file is to add all the external names it contains to the external symbol table; the code of the module is not loaded at this stage. Thereafter (until logoff) these names are available for external linking, which is done automatically when a program referencing any of the names is loaded. It is only necessary to re-install a program file if a change is made to the external names it contains. An external name is the identifier declared as external (standardised to space-free lower-case form) unless this is over-ridden by an alias, in which case the alias name is used instead (exactly as presented). Note that an alias over-rides the declared identifier, rather than providing an alternative to it. \subsection{Cross-calling} In general, data formats and the mechanisms for passing parameters and function results are completely compatible between IMP and Pascal. This applies to full integers, reals, varying strings, records, and arrays. IMP \%name parameters are compatible with Pascal VAR parameters. IMP predicates are compatible with Pascal Boolean functions . The IMP \%byte is storage compatible with the Pascal Char. Integer subrange correspondence is as follows: \small\tt \begin{verbatim} IMP Pascal %short -32768..32767 %half 0..65535 %mite -128..127 %byte 0..255 \end{verbatim}\rm \normalsize \section{Compiler Error Reports} Error reports are kept short to economise on screen space. For reports which relate to a particular component of a statement, the culprit is identified by a marker at the start of the component. \small\tt \begin{verbatim} REPORT MEANING Faulty form statement part indicated is syntactically faulty Unknown atom lexical atom indicated is mis-spelt or unknown Non-starter atom at the start of the statement is not a possible statement introducer Unknown name identifier indicated has not been declared Duplicate identifier indicated has already been declared Mismatch parameters in body of procedure do not match spec Not variable operand in assignment context is not a variable Not reference operand in pointer context is not a reference Wrong type expression is of wrong type for context Wrong class category of identifier is wrong for context Not literal expression in literal context is not literal Inside out upper bound is less than lower Endless loop literal %for loop cannot terminate Out of range operand value is out of range Too few args too few arguments are given for procedure call Too many args too many arguments are given for procedure call Not in loop %exit %or %continue is not within a loop construct Not in routine %return is not within a routine Not in fn/map %result is not within a function or map Not in pred %true/%false is not within a predicate %CYCLE missing %repeat encountered with no matching %cycle %REPEAT missing %end reached with unmatched %cycle %START missing %finish or %else encountered with no matching %start %FINISH missing %end reached with unmatched %start Extra %ELSE %else encountered matching earlier unconditional %else %BEGIN missing %end encountered with no matching %begin or procedure header %END missing %end %of %program or %file reached with unmatched %begin or procedure header %RESULT missing there is apparently a path to the end of a function or map which does not specify a result Not accessible instruction apparently cannot be executed (warning only) Out of order statement appears in incorrect order in block (warning if benign) Nonstandard non-standard language feature (warning only) void identifier is used before a value is assigned to it (warning only) missing forward label or specced identifier does not appear in block (?) missing switch label to which there is an explicit jump has not been specified extra values for too many values for %const or %own array Faulty operand incorrect operand type for machine instruction Wrong size operand is of incorrect size for machine instruction Too complex! compiler limitation exceeded (eg no free register) Internal error ! compiler fault Out of reach! %const or literal string, record or array is not within the range of the machine addressing capability Out of reach! call to procedure specified is not within the range of the machine addressing capability In the case of programs which exceed 32k bytes in size, the compiler uses a number of techniques to avoid creating within-program references which breach the M68000 PC-relative addressing limitation of +-32k. There is a possibility in some cases that these do not succeed, leading to an 'out-of-reach' report. If a name is given in the report, it is that of a procedure which is too distant from one of its calls. If no name is given, the problem is access to a constant. Disastrous errors These reports relate to compiler limits being exceeded. They all cause compilation to be abandoned. Program too big Total size of the compiled code and constants exceeds the maximum allowed for (see Option -KBYTES) Code space exhausted Size of the code for currently open blocks exceeds the maximum allowed for Identifiers too big Total length of all current identifiers exceeds the maximum allowed for (see Option -IDENTS) Too many identifiers Number of current identifiers exceeds the maximum allowed for (see Option -IDENTS) Too many levels Depth of textual nesting of blocks exceeds the maximum permitted (8) Too many literals Internal storage space for literals is exhausted Input ended There is no %endofprogram or %endoffile statement Too many nested includes There are more than three levels of nesting \section{Run-time diagnostics} Errors detected at run-time are reported through the system's exception signalling mechanism (also used for IMP 'events'). If an exception is not trapped, the occurrence of the exception is reported in the form of an error code and text message. In general, the line number at which the failure occurred is provided, but full monitoring of program variables is not at present provided. For most errors, detection at run-time depends on whether particular checking options were selected at compile-time. The availability of a relevant line number depends on having compiled with the option -LINE. The default compile-time options include line numbering and most checks, but not unassigned checks on variables occupying less than 32 bits nor overflow checks for integer addition or subtraction. \subsection{Run-time errors} \small\tt \begin{verbatim} ERROR CODE REQUISITE OPTION Variable value undefined (unassigned) 8 1 -ASS, -BASS, etc [sometimes detected as "Void" at compile-time] Array index out of range 6 2 -ARR Integer arithmetic overflow 1 1 -OVER Real arithmetic overflow 1 2 -OVER Division by zero (integer or real) 1 4 none Trig function error 10 none Assignment value out-of-range 6 1 -CAP Value parameter out-of-range 6 1 -CAP Switch label not catered for taken as at %end [warning issued at compile-time] Name variable NIL 8 1 -ASS Name variable undefined 8 1 -ASS File system error 3 x none Non-numeric character for numeric READ 4 1 End-of-input 9 none \end{verbatim}\rm \normalsize \section{Efficiency} {\hspace*{0.3 in}} . In the absence of floating-point hardware, all floating-point \\ {\hspace*{0.5 in}} operations are performed by software. {\hspace*{0.3 in}} . Integer multiply and divide are also performed by software, although \\ {\hspace*{0.5 in}} a number of special cases are optimised. {\hspace*{0.3 in}} . Full checking is expensive in both time and space. Developed programs \\ {\hspace*{0.5 in}} should be compiled with checks and diagnostics disabled. \\ {\hspace*{0.5 in}} Fullest optimisation is obtained by specifying: {\hspace*{1.0 in}} -NOCHECK-NODIAG-NOSTACK-NOVOL {\hspace*{0.3 in}} . Procedure and function calls are implemented with a minimum of overhead \\ {\hspace*{0.5 in}} so that they may be freely used without significant penalty in all but \\ {\hspace*{0.5 in}} the most time-critical contexts. The space-saving from making full use \\ {\hspace*{0.5 in}} of procedures and functions can be substantial. \section{Low-level facilities} As a system implementation language IMP provides a number of facilities which permit access to parts of the system other languages do not reach. The store-mapping functions (INTEGER, BYTEINTEGER, etc) allow for direct addressing using machine addresses; the name-relative indexing facility (as in CUR[1] or POS[-2]) extends the capability of \%name variables; the fixed-address declaration facility (as in @16\_200C \%byte TIMER, KBIN, KBOUT) allows efficient source-level access to specific areas of store. The use of these facilities involves some loss of the protection normally conferred by a high-level language and a potential (particularly on a processor without hardware protection) for uncontrolled malfunction. They should, therefore, be used with restraint and care. \subsection{Assembler in IMP} Sequences of assembly language instructions may be incorporated in an IMP program at any point. At present no enabling directive is required. Apart from the usual hazards of machine level programming, there is the danger of corrupting the environment pre-supposed by the high-level facilities. For this reason, it is sensible to keep the use of these instructions to a minimum and to take particular care in programming these sections. Assembly language instructions are distinguished from IMP statements by being prefaced by an asterisk (eg *MOVE D0,D1). They appear within IMP blocks and procedures and are executed according to the normal flow of control, subject to any control transfers invoked by the instructions themselves. IMP conventions for statement termination, labelling and commenting apply, but otherwise the form of instruction follows closely that defined under the heading of Assembler Syntax for each individual instruction in the Motorola M68000 manual. Machine-level operands are specified using the mnemonics D0-D7 and A0-A7 (or SP), and the standard syntax for $<$ea$>$ modes. Immediate and Address register variants of op-codes are selected automatically. By comparison with full Assembler, most of the directives do not apply; assembly-time expression evaluation is restricted; size specification in cases where the size is implicit in the op-code is not in general allowed; the indexed PC-relative mode is not supported, nor is the 'current location counter'. The error report 'Faulty operand' indicates use of an invalid operand for the context, but the compiler does not fully check the validity of $<$ea$>$ modes for the particular instruction. NB the default 'size' applied is Long (32-bits) rather than Word (16-bits) which is the manufacturer's default. Programmers may choose to make a practice of including the size suffix explicitly for all relevant instructions. The special mnemonics USP (User Stack Pointer), SR (Status Register) and CCR (Condition Code Register) are NOT supported but the relevant effects can be achieved by use of the additional op-codes: \small\tt \begin{verbatim} MTCCR for MOVE ,CCR MTSR for MOVE ,SR MFSR for MOVE SR, MTUSP An for MOVE An,USP MFUSP An for MOVE USP,An ATCCR # for AND #,CCR ATSR # for AND #,SR ETCCR # for EOR #,CCR ETSR # for EOR #,SR OTCCR # for OR #,CCR OTSR # for OR #,SR \end{verbatim}\rm \normalsize IMP identifiers may also be used as operands for assembly language instructions. The detailed implications of this over the whole range of data types are fairly complex and subject to change. The following cases are reasonably straightforward and stable. Scalar variables or elements of scalar records may be used as $<$ea$>$ operands provided that they are: {\hspace*{0.3 in}} declared as own or \\ {\hspace*{0.3 in}} declared at the outermost level or \\ {\hspace*{0.3 in}} declared at the current level or \\ {\hspace*{0.3 in}} declared by means of a fixed-address declaration Variables declared at intermediate levels should not be accessed since they are not necessarily directly addressable. In the case of a \%name variable the effective operand is the pointer value (32-bit address) rather than the referenced object. Labels and procedure names may be referenced in the Branch group of instructions, including BSR. The only alternative form of operand for these instructions is immediate (eg *BLT \#-4), the value specified being the machine-level displacement. Short and long branches are handled automatically (though the Compiler's CODE listing does not show this). To access a forward label in an assembly language instruction, it is neccesary for the label to have been declared by means of the IMP declaration \%LABEL $<$lab$>$. The registers D0-D3 and A0-A3 may be freely used within assembly sections, but no assumptions can be made about their contents after execution of most IMP statements. Other registers may be used only on the basis that their values are restored before reverting to IMP. In particular this applies to SP. In addition, NOTE WELL that the accessing of local variables depends on SP; if SP is changed, access to such variables in machine instructions becomes a nonsense (though no error report can be made). Similarly, any modification of A4-A6 rules out access to non-local variables. Note that any declaration of IMP identifiers which co-incide with the register mnemonics takes precedence. \vspace{.75in} view:impv2 printed on 06/04/89 at 09.10 \newpage \tableofcontents \end{document}