1555 lines
49 KiB
Text
1555 lines
49 KiB
Text
.\" $Header$
|
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.ds OF \\fBtest~off:~\\fR
|
||
.ds ON \\fBtest~on:~~\\fR
|
||
.ds AL \\fBtest~all:~\\fR
|
||
.ll 72n
|
||
.wh 0 hd
|
||
.wh 60 fo
|
||
.de hd
|
||
'sp 5
|
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..
|
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.de fo
|
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'bp
|
||
..
|
||
.tr ~
|
||
. TITLE
|
||
.de TL
|
||
.sp 15
|
||
.ce
|
||
\\fB\\$1\\fR
|
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..
|
||
. AUTHOR
|
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.de AU
|
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.sp 15
|
||
.ce
|
||
by
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.sp 2
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||
.ce
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\\$1
|
||
..
|
||
. DATE
|
||
.de DA
|
||
.sp 3
|
||
.ce
|
||
( Dated \\$1 )
|
||
..
|
||
. INSTITUTE
|
||
.de VU
|
||
.sp 3
|
||
.ce 4
|
||
Vakgroep Informatica
|
||
Vrije Universiteit
|
||
De Boelelaan 1081
|
||
Amsterdam
|
||
..
|
||
. PARAGRAPH
|
||
.de PP
|
||
.sp
|
||
.ti +5
|
||
..
|
||
.nr CH 0 1
|
||
. CHAPTER
|
||
.de CH
|
||
.nr SH 0 1
|
||
.bp
|
||
.in 0
|
||
\\fB\\n+(CH.~\\$1\\fR
|
||
.PP
|
||
..
|
||
. SUBCHAPTER
|
||
.de SH
|
||
.sp 3
|
||
.in 0
|
||
\\fB\\n(CH.\\n+(SH.~\\$1\\fR
|
||
.PP
|
||
..
|
||
. INDENT START
|
||
.de IS
|
||
.sp
|
||
.in +5
|
||
..
|
||
. INDENT END
|
||
.de IE
|
||
.in -5
|
||
.sp
|
||
..
|
||
. DOUBLE INDENT START
|
||
.de DS
|
||
.sp
|
||
.in +5
|
||
.ll -5
|
||
..
|
||
. DOUBLE INDENT END
|
||
.de DE
|
||
.ll +5
|
||
.in -5
|
||
.sp
|
||
..
|
||
. EQUATION START
|
||
.de EQ
|
||
.sp
|
||
.nf
|
||
..
|
||
. EQUATION END
|
||
.de EN
|
||
.fi
|
||
.sp
|
||
..
|
||
. ITEM
|
||
.de IT
|
||
.sp
|
||
.in 0
|
||
\\fBISO~\\$1:\\fR~\\
|
||
..
|
||
. IMPLEMENTATION 1
|
||
.de I1
|
||
.IS
|
||
.ti -3
|
||
1.~\\
|
||
..
|
||
. IMPLEMENTATION 2
|
||
.de I2
|
||
.sp
|
||
.ti -3
|
||
2.~\\
|
||
..
|
||
.de CS
|
||
.br
|
||
~-~\\
|
||
..
|
||
.br
|
||
.fi
|
||
.TL "Amsterdam Compiler Kit-Pascal reference manual"
|
||
.AU "Johan W. Stevenson"
|
||
.DA "January 4, 1983"
|
||
.VU
|
||
.CH "Introduction"
|
||
This document refers to the (March 1980) ISO standard proposal for Pascal [1].
|
||
Ack-Pascal complies with the requirements of this proposal almost completely.
|
||
The standard requires an accompanying document describing the
|
||
implementation-defined and implementation-dependent features,
|
||
the reaction on errors and the extensions to standard Pascal.
|
||
These four items will be treated in the rest of this document,
|
||
each in a separate chapter.
|
||
The other chapters describe the deviations from the standard and
|
||
the list of options recognized by the compiler.
|
||
.PP
|
||
The Ack-Pascal compiler produces code for an EM machine as defined in [2].
|
||
It is up to the implementor of the EM machine to decide whether errors like
|
||
integer overflow, undefined operand and range bound error are recognized or not.
|
||
For these errors the reaction of some known implementations is given.
|
||
.PP
|
||
There does not (yet) exist a hardware EM machine.
|
||
Therefore, EM programs must be interpreted, or translated into
|
||
instructions for a target machine.
|
||
For the following implementations the behavior is documented:
|
||
.I1
|
||
an interpreter running on a PDP-11.
|
||
Normally the interpreter performs some tests to detect undefined
|
||
integers, integer overflow, range errors, etc.
|
||
However, an option of the interpreter is to skip these tests.
|
||
Another option is to perform some extra tests
|
||
to check for instance the number of actual parameter
|
||
words against the number expected by
|
||
the called procedure.
|
||
We will refer to these modes of operation as 'test all', 'test on' and 'test off'.
|
||
.I2
|
||
a translator into PDP-11 instructions.
|
||
.IE
|
||
.CH "Implementation-defined features"
|
||
For each implementation-defined feature mentioned in the ISO standard
|
||
we give the section number, the quotation from that section and the definition.
|
||
First we quote the definition of implementation-defined:
|
||
.DS
|
||
Those parts of the language which may differ between processors, but which
|
||
will be defined for any particular processor.
|
||
.DE
|
||
.IT 6.1.7
|
||
Each string-character shall denote an implementation-defined value of char-type.
|
||
.IS
|
||
All 7-bits ASCII characters except linefeed LF (10) are allowed.
|
||
Note that an apostrophe ' must be doubled within a string.
|
||
.IE
|
||
.IT 6.4.2.2
|
||
The values of type real shall be an implementation-defined subset
|
||
of the real numbers denoted as specified by 6.1.5.
|
||
.IS
|
||
The format of reals is not defined in EM.
|
||
Even the size of reals depends on the implementation.
|
||
The compiler can be instructed, by the f-option, to use a different
|
||
size for real values.
|
||
The size of reals is preset by the calling program \fIack\fP
|
||
[4] to
|
||
the proper size.
|
||
For each implementation of EM the following constants must be defined:
|
||
epbase: the base for the exponent part
|
||
epprec: the precision of the fraction
|
||
epemin: the minimum exponent
|
||
epemax: the maximum exponent
|
||
.br
|
||
These constants must be chosen so that zero and all numbers with
|
||
exponent e in the range
|
||
.EQ
|
||
epemin <= e <= epemax
|
||
.EN
|
||
and fraction-parts of the form
|
||
.EQ
|
||
f = +_ f\d1\u.b\u-1\d + ... + f\depprec\u.b\u-epprec\d
|
||
.EN
|
||
where
|
||
.EQ
|
||
f\di\u = 0,...,epbase-1 and f\d1\u <> 0
|
||
.EN
|
||
are possible values for reals.
|
||
All other values of type real are considered illegal.
|
||
(See [3] for more information about these constants).
|
||
.br
|
||
For the known EM implementations these constants are:
|
||
.I1
|
||
epbase = 2
|
||
.br
|
||
epprec = 24
|
||
.br
|
||
epemin = -127
|
||
.br
|
||
epemax = +127
|
||
.I2
|
||
ditto
|
||
.IE
|
||
.IT 6.4.2.2
|
||
The type char shall be the enumeration of a set of implementation-defined
|
||
characters, some possibly without graphic representations.
|
||
.IS
|
||
The 7-bits ASCII character set is used, where LF (10) denotes the
|
||
end-of-line marker on text-files.
|
||
.IT 6.4.2.2
|
||
The ordinal numbers of the character values shall be values of integer-type,
|
||
that are implementation-defined, and that are determined by mapping
|
||
the character values on to consecutive non-negative integer values
|
||
starting at zero.
|
||
.IS
|
||
The normal ASCII ordering is used: ord('0')=48, ord('A')=65, ord('a')=97, etc.
|
||
.IE
|
||
.IT 6.4.3.4
|
||
The largest and smallest values of integer-type
|
||
permitted as numbers of a value
|
||
of a set-type shall be implementation-defined.
|
||
.IS
|
||
The smallest value is 0. The largest value is default 15, but can be
|
||
changed by using the i-option of the compiler up to a maximum
|
||
of 32767.
|
||
The compiler allocates as many bits for set-type variables as are necessary
|
||
to store all possible values of the host-type of the base-type of the set,
|
||
rounded up to the nearest multiple of 16.
|
||
If 8 bits are sufficient then only
|
||
8 bits are used if part of a packed structure.
|
||
Thus, the variable s, declared by
|
||
.EQ
|
||
var s: set of '0'..'9';
|
||
.EN
|
||
will contain 128 bits, not 10 or 16.
|
||
These 128 bits are stored in 16 bytes, both for packed and unpacked sets.
|
||
If the host-type of the base-type is integer, then the
|
||
number of bits depends on the i-option.
|
||
The programmer may specify how many bits to allocate for these sets.
|
||
The default is 16, the maximum is 32767.
|
||
The effective number of bits is rounded up to the next multiple of 16, or up
|
||
to 8 if the number of bits is less than or equal to 8.
|
||
Note that the use of set-constructors for sets with more than 256 elements
|
||
is far less efficient than for smaller sets.
|
||
.IT 6.7.2.2
|
||
The predefined constant maxint shall be of integer-type and shall denote
|
||
an implementation-defined value, that satisfies the following conditions:
|
||
.sp 1
|
||
.in +5
|
||
.ti -4
|
||
(a)~All integral values in the closed interval from -maxint to +maxint
|
||
shall be values in the integer-type.
|
||
.ti -4
|
||
(b)~Any monadic operation performed on an integer value in this interval
|
||
shall be correctly performed according to the mathematical rules for
|
||
integer arithmetic.
|
||
.ti -4
|
||
(c)~Any dyadic integer operation on two integer values in this same interval
|
||
shall be correctly performed according to the mathematical rules for
|
||
integer arithmetic, provided that the result is also in this interval.
|
||
.ti -4
|
||
(d)~Any relational operation on two integer values in this same interval
|
||
shall be correctly performed according to the mathematical rules for
|
||
integer arithmetic.
|
||
.in -5
|
||
.IS
|
||
The representation of integers in EM is a \fIn\fP*8-bit word using
|
||
two's complement arithmetic.
|
||
Where \fIn\fP is called wordsize.
|
||
The compiler can only generate code for EM with wordsize 2.
|
||
Thus always:
|
||
.EQ
|
||
maxint = 32767
|
||
.EN
|
||
Because the number -32768 may be used to indicate 'undefined', the
|
||
range of available integers depends on the EM implementation:
|
||
.I1
|
||
\*(ON-32767..+32767.
|
||
.br
|
||
\*(OF-32768..+32767.
|
||
.I2
|
||
-32768..+32767.
|
||
.IE
|
||
.IT 6.9.4.2
|
||
The default TotalWidth values for integer, Boolean and real types
|
||
shall be implementation-defined.
|
||
.IS
|
||
The defaults are:
|
||
integer 6
|
||
Boolean 5
|
||
real 13
|
||
.IT 6.9.4.5.1
|
||
ExpDigits, the number of digits written in an exponent part of a real,
|
||
shall be implementation-defined.
|
||
.IS
|
||
ExpDigits is defined as
|
||
.EQ
|
||
ceil(log10(log10(2 ** epemax)))
|
||
.EN
|
||
For the current implementations this evaluates to 2.
|
||
.IT 6.9.4.5.1
|
||
The character written as part of the representation of
|
||
a real to indicate the beginning of the exponent part shall be
|
||
implementation-defined, either 'E' or 'e'.
|
||
.IS
|
||
The exponent part starts with 'e'.
|
||
.IT 6.9.4.6
|
||
The case of the characters written as representation of the
|
||
Boolean values shall be implementation-defined.
|
||
.IS
|
||
The representations of true and false are 'true' and 'false'.
|
||
.IT 6.9.6
|
||
The effect caused by the standard procedure page
|
||
on a text file shall be implementation-defined.
|
||
.IS
|
||
The ASCII character form feed FF (12) is written.
|
||
.IT 6.10
|
||
The binding of the variables denoted by the program-parameters
|
||
to entities external to the program shall be implementation-defined if
|
||
the variable is of a file-type.
|
||
.IS
|
||
The program parameters must be files and all, except input and output,
|
||
must be declared as such in the program block.
|
||
.PP
|
||
The program parameters input and output, if specified, will correspond
|
||
with the UNIX streams 'standard input' and 'standard output'.
|
||
.PP
|
||
The other program parameters will be mapped to the argument strings
|
||
provided by the caller of this program.
|
||
The argument strings are supposed to be path names of the files to be
|
||
opened or created.
|
||
The order of the program parameters determines the mapping:
|
||
the first parameter is mapped onto the first argument string etc.
|
||
Note that input and output are ignored in this mapping.
|
||
.PP
|
||
The mapping is recalculated each time a program parameter
|
||
is opened for reading or writing by a call to the standard procedures
|
||
reset or rewrite.
|
||
This gives the programmer the opportunity to manipulate the list
|
||
of string arguments using the external procedures argc, argv and argshift
|
||
available in libpc [7].
|
||
.IT 6.10
|
||
The effect of an explicit use of reset or rewrite
|
||
on the standard textfiles input or output shall be implementation-defined.
|
||
.IS
|
||
The procedures reset and rewrite are no-ops
|
||
if applied to input or output.
|
||
.CH "Implementation-dependent features"
|
||
For each implementation-dependent feature mentioned in the ISO standard draft,
|
||
we give the section number, the quotation from that section and the way
|
||
this feature is treated by the Ack-Pascal system.
|
||
First we quote the definition of 'implementation-dependent':
|
||
.DS
|
||
Those parts of the language which may differ between processors,
|
||
and for which there need not be a definition for a particular processor.
|
||
.DE
|
||
.IT 5.1.1
|
||
The method for reporting errors or warnings shall be implementation-dependent.
|
||
.IS
|
||
The error handling is treated in a following chapter.
|
||
.IE
|
||
.IT 6.1.4
|
||
Other implementation-dependent directives may be defined.
|
||
.IS
|
||
Except for the required directive 'forward' the Ack-Pascal compiler recognizes
|
||
only one directive: 'extern'.
|
||
This directive tells the compiler that the procedure block of this
|
||
procedure will not be present in the current program.
|
||
The code for the body of this procedure must be included at a later
|
||
stage of the compilation process.
|
||
.PP
|
||
This feature allows one to build libraries containing often used routines.
|
||
These routines do not have to be included in all the programs using them.
|
||
Maintenance is much simpler if there is only one library module to be
|
||
changed instead of many Pascal programs.
|
||
.PP
|
||
Another advantage is that these library modules may be written in a different
|
||
language, for instance C or the EM assembly language.
|
||
This is useful if you want to use some specific EM instructions not generated
|
||
by the Pascal compiler. Examples are the system call routines and some
|
||
floating point conversion routines.
|
||
Another motive could be the optimization of some time-critical program parts.
|
||
.PP
|
||
The use of external routines, however, is dangerous.
|
||
The compiler normally checks for the correct number and type of parameters
|
||
when a procedure is called and for the result type of functions.
|
||
If an external routine is called these checks are not sufficient,
|
||
because the compiler can not check whether the procedure heading of the
|
||
external routine as given in the Pascal program matches the actual routine
|
||
implementation.
|
||
It should be the loader's task to check this.
|
||
However, the current loaders are not that smart.
|
||
Another solution is to check at run time, at least the number of words
|
||
for parameters. Some EM implementations check this:
|
||
.I1
|
||
\*(ALthe number of words passed as parameters is checked, but this will not catch all faulty cases.
|
||
.br
|
||
\*(ONnot checked.
|
||
.I2
|
||
not checked.
|
||
.IE
|
||
.PP
|
||
For those who wish the use the interface between C and Pascal we
|
||
give an incomplete list of corresponding formal parameters in C and Pascal.
|
||
.sp 1
|
||
.TS
|
||
l l.
|
||
Pascal C
|
||
a:integer int a
|
||
a:char int a
|
||
a:boolean int a
|
||
a:real double a
|
||
a:^type type *a
|
||
var a:type type *a
|
||
procedure a(pars) struct {
|
||
void (*a)() ;
|
||
char *static_link ;
|
||
}
|
||
function a(pars):type struct {
|
||
type (*a)() ;
|
||
char *static_link ;
|
||
}
|
||
.TE
|
||
The Pascal runtime system uses the following algorithm when calling
|
||
function/procedures passed as parameters.
|
||
.TS
|
||
l l.
|
||
if ( static_link ) (*a)(static_link,pars) ;
|
||
else (*a)(pars) ;
|
||
.TE
|
||
.IT 6.7.2.1
|
||
The order of evaluation of the operands of a dyadic operator
|
||
shall be implementation-dependent.
|
||
.IS
|
||
Operands are always evaluated, so the program part
|
||
.EQ
|
||
if (p<>nil) and (p^.value<>0) then
|
||
.EN
|
||
is probably incorrect.
|
||
.PP
|
||
The left-hand operand of a dyadic operator is almost always evaluated
|
||
before the right-hand side.
|
||
Some peculiar evaluations exist for the following cases:
|
||
.IS
|
||
.ti -3
|
||
1.~\
|
||
the modulo operation is performed by a library routine to
|
||
check for negative values of the right operand.
|
||
.IE
|
||
.sp
|
||
.ti -3
|
||
2.~\
|
||
the expression
|
||
.EQ
|
||
set1 <= set2
|
||
.EN
|
||
where set1 and set2 are compatible set types is evaluated in the
|
||
following steps:
|
||
.IS
|
||
.CS
|
||
evaluate set2
|
||
.CS
|
||
evaluate set1
|
||
.CS
|
||
compute set2+set1
|
||
.CS
|
||
test set2 and set2+set1 for equality
|
||
.IE
|
||
This is the only case where the right-hand side is computed first.
|
||
.sp
|
||
.ti -3
|
||
3.~\
|
||
the expression
|
||
.EQ
|
||
set1 >= set2
|
||
.EN
|
||
where set1 and set2 are compatible set types is evaluated in the following steps:
|
||
.IS
|
||
.CS
|
||
evaluate set1
|
||
.CS
|
||
evaluate set2
|
||
.CS
|
||
compute set1+set2
|
||
.CS
|
||
test set1 and set1+set2 for equality
|
||
.IE
|
||
.IT 6.7.3
|
||
The order of evaluation, accessing and binding
|
||
of the actual-parameters for functions
|
||
shall be implementation-dependent.
|
||
.IS
|
||
The order of evaluation is from right to left.
|
||
.IT 6.8.2.2
|
||
If access to the variable in an assignment-statement involves the indexing of an array
|
||
and/or a reference to a field within a variant of a record
|
||
and/or the de-referencing of a pointer-variable
|
||
and/or a reference to a buffer-variable,
|
||
the decision whether these actions precede or follow the evaluation
|
||
of the expression shall be implementation-dependent.
|
||
.IS
|
||
The expression is evaluated first.
|
||
.IT 6.8.2.3
|
||
The order of evaluation and binding of the actual-parameters for procedures
|
||
shall be implementation-dependent.
|
||
.IS
|
||
The same as for functions.
|
||
.IT 6.9.6
|
||
The effect of inspecting a text file to which the page
|
||
procedure was applied during generation is
|
||
implementation-dependent.
|
||
.IS
|
||
The formfeed character written by page is
|
||
treated like a normal character, with ordinal value 12.
|
||
.IT 6.10
|
||
The binding of the variables denoted by the program-parameters
|
||
to entities external to the program shall be implementation-dependent unless
|
||
the variable is of a file-type.
|
||
.IS
|
||
Only variables of a file-type are allowed as program parameters.
|
||
.IE
|
||
.CH "Error handling"
|
||
There are three classes of errors to be distinguished.
|
||
In the first class are the error messages generated by the compiler.
|
||
The second class consists of the occasional errors generated by the other
|
||
programs involved in the compilation process.
|
||
Errors of the third class are the errors as defined in the standard by:
|
||
.DS
|
||
An error is a violation by a program of the requirements of this standard
|
||
such that detection normally requires execution of the program.
|
||
.DE
|
||
.SH "Compiler errors"
|
||
The error messages (and the listing) are not generated by the compiler itself.
|
||
The compiler only detects errors and writes the errors in condensed form on
|
||
an intermediate file.
|
||
Each error in condensed form contains:
|
||
.IS
|
||
.CS
|
||
an optional error message parameter (identifier or number).
|
||
.CS
|
||
an error number
|
||
.CS
|
||
a line number
|
||
.CS
|
||
a column number.
|
||
.IE
|
||
Every time the compiler detects an error that does not have influence
|
||
on the code produced by the compiler or on the syntax decisions, a warning
|
||
messages is given.
|
||
If only warnings are generated, compilation proceeds and probably results
|
||
in a correctly compiled program.
|
||
.PP
|
||
The intermediate error file is read by the interface program
|
||
\fIack\fP [4],
|
||
that produces the error messages.
|
||
It uses an other file, the error message file,
|
||
to find an error script line.
|
||
Whenever this error script line contains the character '%', the error messages
|
||
parameter is substituted.
|
||
For negative error numbers the message constructed is prepended with 'Warning: '.
|
||
.PP
|
||
Sometimes the compiler produces several errors for the same file position
|
||
(line number, column number).
|
||
Only the first of these messages is given, because the others are probably
|
||
directly caused by the first one.
|
||
If the first one is a warning while one of its successors for that position
|
||
is a fatal message, then the warning is promoted to a fatal one.
|
||
However, parameterized messages are always given.
|
||
.PP
|
||
The error messages and listing come in three flavors, selected by flags
|
||
given to \fIack\fP [4]:
|
||
.in +10
|
||
.sp
|
||
.ti -8
|
||
default:no listing, one line per error giving the file name
|
||
of the Pascal source file, the line number and the error messages.
|
||
.sp
|
||
.ti -8
|
||
-e:~~~~~for each erroneous line a listing of the line and its predecessor.
|
||
The next line contains one or more characters '^' pointing to the
|
||
places where an error is detected.
|
||
For each error on that line a message follows.
|
||
.sp
|
||
.ti -8
|
||
-E:~~~~~same as for '-e', except that all source lines are listed,
|
||
even if the program is perfect.
|
||
.IE
|
||
.IE
|
||
.SH "Other errors detected at compilation time"
|
||
Two main categories: file system problems and table overflow.
|
||
Problems with the file system may be caused by protection (you may not read
|
||
or create files) or by space problems (no space left on device; out of inodes;
|
||
too many processes).
|
||
Table overflow problems are often caused by peculiar source programs:
|
||
very long procedures or functions, a lot of strings.
|
||
Table overflow problems can sometimes be cured
|
||
by giving a flag (-sl when producing e.out files) to \fIack\fP [4].
|
||
.PP
|
||
Extensive treatment of these errors is outside the scope of this manual.
|
||
.SH "Runtime errors"
|
||
Errors detected at run time cause an error message to be generated on the
|
||
diagnostic output stream (UNIX file descriptor 2).
|
||
The message consists of the name of the program followed by a message
|
||
describing the error, possibly followed by the source line number.
|
||
Unless the l-option is turned off, the compiler generates code to keep track
|
||
of which source line causes which EM instructions to be generated.
|
||
It depends on the EM implementation whether these LIN instructions
|
||
are skipped or executed:
|
||
.I1
|
||
LIN instructions are always executed. The old line number is saved and
|
||
restored whenever a procedure or function is called.
|
||
All error messages contain this line number, except when the l-option
|
||
was turned off.
|
||
.I2
|
||
same as above, but line numbers are not saved when procedures and functions
|
||
are called.
|
||
.IE
|
||
For each error mentioned in the standard we give the section number,
|
||
the quotation from that section and the way it is processed by the
|
||
Pascal-compiler or runtime system.
|
||
.PP
|
||
For detected errors the corresponding message
|
||
and trap number are given.
|
||
Trap numbers are useful for exception-handling routines.
|
||
Normally, each error causes the program to terminate.
|
||
By using exception-handling routines one can
|
||
ignore errors or perform alternate actions.
|
||
Only some of the errors can be ignored
|
||
by restarting the failing instruction.
|
||
These errors are marked as non-fatal,
|
||
all others as fatal.
|
||
A list of errors with trap number between 0 and 63
|
||
(EM errors) can be found in [2].
|
||
Errors with trap number between 64 and 127 (Pascal errors) are listed in [8].
|
||
.IT 6.4.3.3
|
||
It shall be an error if any field-identifier defined within a variant
|
||
is used in a field-designator unless the value of the tag-field
|
||
is associated with that variant.
|
||
.IS
|
||
This error is not detected.
|
||
Sometimes this feature is used to achieve easy type conversion.
|
||
However, using record variants this way is dangerous, error prone and not portable.
|
||
.IT 6.4.6
|
||
It shall be an error if a value of type T2 must be
|
||
assignment-compatible with type T1, while
|
||
T1 and T2 are compatible ordinal-types and the value of
|
||
type T2 is not in the closed interval specified by T1.
|
||
.IS
|
||
The compiler distinguishes between array-index expressions and the other
|
||
places where assignment-compatibility is required.
|
||
.PP
|
||
Array subscripting is done using the EM array instructions.
|
||
These instructions have three arguments: the array base address,
|
||
the index and the address of the array descriptor.
|
||
An array descriptor describes one dimension by three values:
|
||
the element size, the lower bound on the index and the number of elements
|
||
minus one.
|
||
It depends on the EM implementation whether these bounds are checked:
|
||
.I1
|
||
\*(ONchecked (array bound error, trap 0, non-fatal).
|
||
.br
|
||
\*(OFnot checked
|
||
.I2
|
||
not checked.
|
||
.IE
|
||
The other places where assignment-compatibility is required are:
|
||
.IS
|
||
.CS
|
||
assignment
|
||
.CS
|
||
value parameters
|
||
.CS
|
||
procedures read and readln
|
||
.CS
|
||
the final value of the for-statement
|
||
.IE
|
||
For these places the compiler generates an EM range check instruction, except
|
||
when the r-option is turned off, or when the range of values of T2
|
||
is enclosed in the range of T1.
|
||
If the expression consists of a single variable and if that variable
|
||
is of a subrange type,
|
||
then the subrange type itself is taken as T2, not its host-type.
|
||
Therefore, a range instruction is only generated if T1 is a subrange type
|
||
and if the expression is a constant, an expression with two or more
|
||
operands, or a single variable with a type not enclosed in T1.
|
||
If a constant is assigned, then the EM optimizer removes the range check
|
||
instruction, except when the value is out of bounds.
|
||
.PP
|
||
It depends on the EM implementation whether the range check instruction
|
||
is executed or skipped:
|
||
.I1
|
||
\*(ONchecked (range bound error, trap 1, non-fatal).
|
||
.br
|
||
\*(OFskipped
|
||
.I2
|
||
skipped
|
||
.IE
|
||
.IT 6.4.6
|
||
It shall be an error if a value of type T2 must be
|
||
assignment-compatible with type T1, while T1 and T2 are compatible
|
||
set-types and any member of the value of type T2
|
||
is not in the closed interval specified by the base-type
|
||
of the type T1.
|
||
.IS
|
||
This error is not detected.
|
||
.IT 6.5.4
|
||
It shall be an error if
|
||
the pointer-variable has a nil-value or is undefined at the time
|
||
it is de-referenced.
|
||
.IS
|
||
The EM definition does not specify the binary representation of pointer
|
||
values, so that it is not possible to choose an otherwise illegal
|
||
binary representation for the pointer value NIL.
|
||
Rather arbitrary the compiler uses the integer value zero to represent NIL.
|
||
For all current implementations this does not cause problems.
|
||
.PP
|
||
The size of pointers depends on the implementation and is
|
||
preset in the compiler by \fIack\fP [4].
|
||
The compiler can be instructed, by the p-option, to use
|
||
any size for pointer objects.
|
||
NIL is represented here by the appropriate number of zero words.
|
||
.PP
|
||
It depends on the EM implementation whether de-referencing of a pointer
|
||
with value NIL causes an error:
|
||
.I1
|
||
\*(ONfor every de-reference the pointer value is checked to be legal.
|
||
The value NIL is always illegal.
|
||
Objects addressed by a NIL pointer always cause an error, except
|
||
when they are part of some extraordinary sized structure
|
||
(bad pointer, trap 22, fatal).
|
||
.br
|
||
\*(OFde-referencing for fetching will not cause
|
||
an error to occur.
|
||
However, if the pointer value is used for a store operation,
|
||
a segmentation violation probably results (memory fault, trap 21, fatal).
|
||
(Note: this is only true if the interpreter is executed with coinciding
|
||
address spaces and protected text part. The interpreter must therefore
|
||
be loaded with the '-n' option of the UNIX loader [5]).
|
||
.I2
|
||
de-referencing for a fetch operation will not cause an error.
|
||
A store operation probably causes an error if the '-n' flag is
|
||
specified to \fIack\fP [4] or ld [5] while loading your program.
|
||
.IE
|
||
Some implementations of EM initialize all memory cells for newly
|
||
created variables with a constant that probably causes an error if that variable
|
||
is not initialized with a value of its own type before use.
|
||
For each implementation we give whether memory cells are initialized,
|
||
with what value, and whether this value causes an error if de-referenced.
|
||
.I1
|
||
each memory word is initialized with the bit representation 1000000000000000,
|
||
representing -32768 in 2's complement notation.
|
||
For most small and medium sized programs this value will cause a segmentation
|
||
violation (memory fault, trap 21, fatal).
|
||
.I2
|
||
no initialization.
|
||
Whenever a pointer is de-referenced, without being properly initialized,
|
||
a segmentation violation (memory fault, trap 21, fatal)
|
||
or 'bus error' are possible.
|
||
.IE
|
||
.IT 6.5.5
|
||
It shall be an error if the value of a file-variable f is altered
|
||
while the buffer-variable is an actual variable parameter, or
|
||
an element of the record-variable-list of a with-statement, or both.
|
||
.IS
|
||
This error is not detected
|
||
.IT 6.5.5
|
||
It shall be an error if the value of a file-variable f is altered
|
||
by an assignment-statement which contains the buffer-variable f^ in
|
||
its left-hand side.
|
||
.IS
|
||
This error is not detected.
|
||
.IT 6.6.5.2
|
||
It shall be an error if
|
||
the stated pre-assertion does not hold immediately
|
||
prior to any use of the file handling procedures
|
||
rewrite, put, reset and get.
|
||
.IS
|
||
For each of these four operations the pre-assertions
|
||
can be reformulated as:
|
||
.sp
|
||
rewrite(f):~no pre-assertion.
|
||
.br
|
||
put(f):~~~~~f is opened for writing and f^ is not undefined.
|
||
.br
|
||
reset(f):~~~f exists.
|
||
.br
|
||
get(f):~~~~~f is opened for reading and eof(f) is false.
|
||
.sp
|
||
The following errors are detected for these operations:
|
||
.sp
|
||
rewrite(f):
|
||
.in +10
|
||
.ti -5
|
||
more args expected, trap 64, fatal:
|
||
.br
|
||
f is a program-parameter and the corresponding
|
||
file name is not supplied by the caller of the program.
|
||
.ti -5
|
||
rewrite error, trap 101, fatal:
|
||
.br
|
||
the caller of the program lacks the necessary
|
||
access rights to create the file in the file system
|
||
or operating system problems like table overflow
|
||
prevent creation of the file.
|
||
.in -10
|
||
.sp
|
||
put(f):
|
||
.in +10
|
||
.ti -5
|
||
file not yet open, trap 72, fatal:
|
||
.br
|
||
reset or rewrite are never applied to the file.
|
||
The checks performed by the run time system are not foolproof.
|
||
.ti -5
|
||
not writable, trap 96, fatal:
|
||
.br
|
||
f is opened for reading.
|
||
.ti -5
|
||
write error, trap 104, fatal:
|
||
.br
|
||
probably caused by file system problems.
|
||
For instance, the file storage is exhausted.
|
||
Because IO is buffered to improve performance,
|
||
it might happen that this error occurs if the
|
||
file is closed.
|
||
Files are closed whenever they are rewritten or reset, or on
|
||
program termination.
|
||
.in -10
|
||
.sp
|
||
reset(f):
|
||
.in +10
|
||
.ti -5
|
||
more args expected, trap 64, fatal:
|
||
.br
|
||
same as for rewrite(f).
|
||
.ti -5
|
||
reset error, trap 100, fatal:
|
||
.br
|
||
f does not exist, or the caller has insufficient access rights, or
|
||
operating system tables are exhausted.
|
||
.in -10
|
||
.sp
|
||
get(f):
|
||
.in +10
|
||
.ti -5
|
||
file not yet open, trap 72, fatal:
|
||
.br
|
||
as for put(f).
|
||
.ti -5
|
||
not readable, trap 97, fatal:
|
||
.br
|
||
f is opened for writing.
|
||
.ti -5
|
||
end of file, trap 98, fatal:
|
||
.br
|
||
eof(f) is true just before the call to get(f).
|
||
.ti -5
|
||
read error, trap 103, fatal:
|
||
.br
|
||
unlikely to happen. Probably caused by hardware problems
|
||
or by errors elsewhere in your program that destroyed
|
||
the file information maintained by the run time system.
|
||
.ti -5
|
||
truncated, trap 99, fatal:
|
||
.br
|
||
the file is not properly formed by an integer
|
||
number of file elements.
|
||
For instance, the size of a file of integer is odd.
|
||
.ti -5
|
||
non-ASCII char read, trap 106, non-fatal:
|
||
.br
|
||
the character value of the next character-type
|
||
file element is out of range (0..127).
|
||
Only for text files.
|
||
.in -10
|
||
.IT 6.6.5.3
|
||
It shall be an error to change any variant-part of a variable
|
||
allocated by the form new(p,c1,...,cn) from the variant specified.
|
||
.IS
|
||
This error is not detected.
|
||
.IT 6.6.5.3
|
||
It shall be an error if a variable to be disposed had been allocated
|
||
using the form new(p,c1,...,cn) with more variants specified than
|
||
specified to dispose.
|
||
.IS
|
||
This error can cause more memory to be freed then was allocated.
|
||
Dispose causes a fatal trap 73 when memory already on the free
|
||
list is freed again.
|
||
.IT 6.6.5.3
|
||
It shall be an error if the variants of a variable to be disposed
|
||
are different from those specified by the case-constants to dispose.
|
||
.IS
|
||
This error is not detected.
|
||
.IT 6.6.5.3
|
||
It shall be an error if the value of the pointer parameter of dispose has
|
||
nil-value or is undefined.
|
||
.IS
|
||
The same comments apply as for de-referencing NIL or undefined pointers.
|
||
.IT 6.6.5.3
|
||
It shall be an error if a variable that is identified by the pointer parameter
|
||
of dispose (or a component thereof) is currently either an actual
|
||
variable parameter, or an element of the record-variable-list of a
|
||
with-statement, or both.
|
||
.IS
|
||
This error is not detected.
|
||
.IT 6.6.5.3
|
||
It shall be an error if a referenced-variable created using the second form
|
||
of new is used in its entirety
|
||
as an operand in an expression, or as the variable in an assignment-statement
|
||
or as an actual-parameter.
|
||
.IS
|
||
This error is not detected.
|
||
.IT 6.6.6.2
|
||
It shall be an error if the mathematical defined result of an
|
||
arithmetic function would fall outside the set of values
|
||
of the indicated result.
|
||
.IS
|
||
Except for the errors for undefined arguments,
|
||
the following errors may occur for the arithmetic functions:
|
||
.in +16
|
||
.ti -11
|
||
abs(x):~~~~none.
|
||
.ti -11
|
||
sqr(x):~~~~real underflow, trap 5, non-fatal;
|
||
.br
|
||
real overflow, trap 4, non-fatal
|
||
.ti -11
|
||
sin(x):~~~~real underflow, trap 5, non-fatal
|
||
.ti -11
|
||
cos(x):~~~~real underflow, trap 5, non-fatal
|
||
.ti -11
|
||
exp(x):~~~~error in exp, trap 65, non-fatal (if x>10000);
|
||
.br
|
||
real underflow, trap 5, non-fatal;
|
||
.br
|
||
real overflow, trap 4, non-fatal
|
||
.ti -11
|
||
ln(x):~~~~~error in ln, trap 66, non-fatal ( if x<=0)
|
||
.ti -11
|
||
sqrt(x):~~~error in sqrt, trap 67, non-fatal (if x<0)
|
||
.ti -11
|
||
arctan(x):~real underflow, trap 5, non-fatal;
|
||
.br
|
||
real overflow, trap 4, non-fatal
|
||
.in -16
|
||
.IE
|
||
.IT 6.6.6.2
|
||
It shall be an error if x in ln(x) is not greater than zero.
|
||
.IS
|
||
See above.
|
||
.IT 6.6.6.2
|
||
It shall be an error if x in sqrt(x) is negative.
|
||
.IS
|
||
See above.
|
||
.IT 6.6.6.2
|
||
It shall be an error if
|
||
the integer value of trunc(x) does not exist.
|
||
.IS
|
||
This error is detected (conversion error, trap 10, non-fatal).
|
||
.IT 6.6.6.2
|
||
It shall be an error if
|
||
the integer value of round(x) does not exist.
|
||
.IS
|
||
This error is detected (conversion error, trap 10, non-fatal).
|
||
.IT 6.6.6.2
|
||
It shall be an error if
|
||
the integer value of ord(x) does not exist.
|
||
.IS
|
||
This error can not occur, because the compiler will not allow
|
||
such ordinal types.
|
||
.IT 6.6.6.2
|
||
It shall be an error if
|
||
the character value of chr(x) does not exist.
|
||
.IS
|
||
Except when the r-option is turned off, the compiler generates an EM
|
||
range check instruction. The effect of this instruction depends on the
|
||
EM implementation as described before.
|
||
.IT 6.6.6.2
|
||
It shall be an error if the value of succ(x) does not exist.
|
||
.IS
|
||
Same comments as for chr(x).
|
||
.IT 6.6.6.2
|
||
It shall be an error if the value of pred(x) does not exist.
|
||
.IS
|
||
Same comments as for chr(x).
|
||
.IT 6.6.6.5
|
||
It shall be an error if
|
||
f in eof(f) is undefined.
|
||
.IS
|
||
This error is detected (file not yet open, trap 72, fatal).
|
||
.IT 6.6.6.5
|
||
It shall be an error if
|
||
f in eoln(f) is undefined, or if eof(f) is true at that time.
|
||
.IS
|
||
The following errors may occur:
|
||
.IS
|
||
file not yet open, trap 72, fatal;
|
||
.br
|
||
not readable, trap 97, fatal;
|
||
.br
|
||
end of file, trap 98, fatal.
|
||
.IE
|
||
.IT 6.7.1
|
||
It shall be an error if any variable or function used as an operand in an expression is
|
||
undefined at the time of its use.
|
||
.IS
|
||
Detection of undefined operands is only possible if there is at least one bit
|
||
representation that is not allowed as legal value.
|
||
The set of legal values depends on the type of the operand.
|
||
To detect undefined operands, all newly created variables must be assigned
|
||
a value illegal for the type of the created variable.
|
||
The compiler itself does not generate code to initialize newly created variables.
|
||
Instead, the compiler generates code to allocate some new memory cells.
|
||
It is up to the EM implementation to initialize these memory cells.
|
||
However, the EM machine does not know the types of the variables for which
|
||
memory cells are allocated.
|
||
Therefore, the best an EM implementation can do is to initialize with a value
|
||
that is illegal for the most common types of operands.
|
||
.PP
|
||
For all current EM implementations we will describe whether memory cells
|
||
are initialized, which value is used to initialize, for each operand type
|
||
whether that value is illegal, and for all operations on all operand
|
||
types whether that value is detected as undefined.
|
||
.I1
|
||
\*(ONnew memory words are initialized with -32768.
|
||
Assignment of this value is always allowed. Errors may occur
|
||
whenever undefined operands are used in operations.
|
||
.br
|
||
.ul
|
||
integer:
|
||
-32768 is illegal. All arithmetic operations (except unary +) cause
|
||
an error (undefined integer, trap 8, non-fatal).
|
||
Relational operations do not, except for IN when the left operand is undefined.
|
||
Printing of -32768 using write is allowed.
|
||
.br
|
||
.ul
|
||
real:
|
||
the bit representation of a real, caused by initializing the constituent
|
||
memory words with -32768, is illegal.
|
||
All arithmetic and relational operations (except unary +) cause an error
|
||
(real undefined, trap 9, non-fatal).
|
||
Printing causes the same error.
|
||
.br
|
||
.ul
|
||
char:
|
||
the value -32768 is illegal. For objects of type 'packed array[] of char'
|
||
half the characters will have the value chr(0), which is legal, and the
|
||
others will have the value chr(128), outside the valid ASCII range.
|
||
The relational operators, however, do not cause an error.
|
||
.br
|
||
.ul
|
||
Boolean:
|
||
the value -32768 is illegal. For objects of type 'packed array[] of boolean'
|
||
half the booleans will have the value false, while the others have the value v,
|
||
where ord(v) = 128, naturally illegal.
|
||
However, the Boolean and relational operations do not cause an error.
|
||
.br
|
||
.ul
|
||
set:
|
||
undefined operands of type set can not be distinguished from
|
||
properly initialized ones.
|
||
The set and relational operations, therefore, can never cause an error.
|
||
However, if one forgets to initialize a set of character, then spurious
|
||
characters like '/', '?', 'O', '_' and 'o' appear.
|
||
.sp
|
||
\*(OFnew memory cells are initialized with -32768.
|
||
The only cases where this value causes an error are when
|
||
an undefined operand of type real is used in an arithmetic or relational
|
||
operation (except unary +) or when an undefined real is used as an
|
||
argument to a standard function.
|
||
.I2
|
||
Newly created memory cells are not initialized and therefore
|
||
they have a random value.
|
||
.IT 6.7.1
|
||
It shall be an error if
|
||
the value of any member denoted by any member-designator of the
|
||
set-constructor is outside the implementation-defined limits.
|
||
.IS
|
||
This error is detected (set bound error, trap 2, non-fatal).
|
||
.IT 6.7.1
|
||
It shall be an error if
|
||
the possible types of an set-constructor do not permit it
|
||
to assume a suitable type.
|
||
.IS
|
||
The compiler allocates as many bits as are necessary to store all
|
||
elements of the host-type of the base-type of the set, not the
|
||
base-type itself.
|
||
Therefore, all possible errors can be detected at compile time.
|
||
.IT 6.7.2.2
|
||
It shall be an error if j is zero in 'i div j'.
|
||
.IS
|
||
It depends on the EM implementation whether this error is detected:
|
||
.I1
|
||
\*(ONdetected (divide by 0, trap 6, non-fatal).
|
||
.br
|
||
\*(OFnot detected.
|
||
.I2
|
||
not detected.
|
||
.IE
|
||
.IT 6.7.2.2
|
||
It shall be an error if
|
||
j is zero or negative in i MOD j.
|
||
.IS
|
||
This error is detected (only positive j in 'i mod j', trap 71, non-fatal).
|
||
.IT 6.7.2.2
|
||
It shall be an error if the result of any operation on integer
|
||
operands is not performed according to the mathematical
|
||
rules for integer arithmetic.
|
||
.IS
|
||
The reaction depends on the EM implementation:
|
||
.I1
|
||
\*(ONerror detected if
|
||
.EQ
|
||
(result >= 32768) or (result < -32768).
|
||
.EN
|
||
(integer overflow, trap 3, non-fatal).
|
||
Note that if the result is -32768 the use of this value in further operations
|
||
may cause an error.
|
||
.br
|
||
\*(OFnot detected.
|
||
.I2
|
||
not detected.
|
||
.IT 6.8.3.5
|
||
It shall be an error if none of the case-constants is equal to the value of the
|
||
case-index upon entry to the case-statement.
|
||
.IS
|
||
This error is detected (case error, trap 20, fatal).
|
||
.IT 6.8.3.9
|
||
It shall be an error if the final-value of a for-statement is not
|
||
assignment-compatible with the control-variable when the
|
||
initial-value is assigned to the control-variable.
|
||
.IS
|
||
It is detected if the control variable leaves
|
||
its allowed range of values while stepping
|
||
from initial to final value.
|
||
This is equivalent with the requirements if the
|
||
for-statement is not terminated before
|
||
the final value is reached.
|
||
.IT 6.9.2
|
||
It shall be an error if the sequence of characters read looking for an integer does not
|
||
form a signed-integer as specified in 6.1.5.
|
||
.IS
|
||
This error is detected (digit expected, trap 105, non-fatal).
|
||
.IT 6.9.2
|
||
It shall be an error if the sequence of characters read looking for a real does not
|
||
form a signed-number as specified in 6.1.5.
|
||
.IS
|
||
This error is detected (digit expected, trap 105, non-fatal).
|
||
.IT 6.9.2
|
||
It shall be an error if read is applied to f while f is undefined or
|
||
not opened for reading.
|
||
.IS
|
||
This error is detected (see get(f)).
|
||
.IT 6.9.4
|
||
It shall be an error if write is applied to f while f is undefined or
|
||
not opened for writing.
|
||
.IS
|
||
This error is detected (see put(f)).
|
||
.IT 6.9.4
|
||
It shall be an error if TotalWidth or FracDigits as specified in
|
||
write or writeln procedure calls are less than one.
|
||
.IS
|
||
This error is not detected. Moreover, it is considered an extension to
|
||
allow zero or negative values.
|
||
.IT 6.9.6
|
||
It shall be an error if page is applied to f while f is undefined or
|
||
not opened for writing.
|
||
.IS
|
||
This error is detected (see put(f)).
|
||
.CH "Extensions to the standard"
|
||
.IS
|
||
.ti -3
|
||
1.~\
|
||
Separate compilation.
|
||
.sp
|
||
The compiler is able to (separately) compile a collection of declarations,
|
||
procedures and functions to form a library.
|
||
The library may be linked with the main program, compiled later.
|
||
The syntax of these modules is
|
||
.EQ
|
||
module = [constant-definition-part]
|
||
[type-definition-part]
|
||
[var-declaration-part]
|
||
[procedure-and-function-declaration-part]
|
||
.EN
|
||
The compiler accepts a program or a module:
|
||
.EQ
|
||
unit = program | module
|
||
.EN
|
||
All variables declared outside a module must be imported
|
||
by parameters, even the files input and output.
|
||
Access to a variable declared in a module is only possible
|
||
using the procedures and functions declared in that same module.
|
||
By giving the correct procedure/function heading followed by the
|
||
directive 'extern' you may use procedures and functions declared in
|
||
other units.
|
||
.sp
|
||
.ti -3
|
||
2.~\
|
||
Assertions.
|
||
.sp
|
||
The Ack-Pascal compiler recognizes an additional statement, the assertion.
|
||
Assertions can be used as an aid in debugging and documentation.
|
||
The syntax is:
|
||
.EQ
|
||
assertion = 'assert' Boolean-expression
|
||
.EN
|
||
An assertion is a simple-statement, so
|
||
.EQ
|
||
simple-statement = [assignment-statement |
|
||
procedure-statement |
|
||
goto-statement |
|
||
assertion
|
||
]
|
||
.EN
|
||
An assertion causes an error if the Boolean-expression is false.
|
||
That is its only purpose.
|
||
It does not change any of the variables, at least it should not.
|
||
Therefore, do not use functions with side-effects in the Boolean-expression.
|
||
If the a-option is turned off, then assertions are skipped by the
|
||
compiler. 'assert' is not a word-symbol (keyword) and may be used as identifier.
|
||
However, assignment to a variable and calling of a procedure with that name will be impossible.
|
||
.sp
|
||
.ti -3
|
||
3.~\
|
||
Additional procedures.
|
||
.sp
|
||
Three additional standard procedures are available:
|
||
.IS
|
||
.IS
|
||
.ti -8
|
||
halt:~~~a call of this procedure is equivalent to jumping to the
|
||
end of your program. It is always the last statement executed.
|
||
The exit status of the program may be supplied
|
||
as optional argument.
|
||
.ti -8
|
||
release:
|
||
.ti -8
|
||
mark:~~~for most applications it is sufficient to use the heap as second stack.
|
||
Mark and release are suited for this type of use, more suited than dispose.
|
||
mark(p), with p of type pointer, stores the current value of the
|
||
heap pointer in p. release(p), with p initialized by a call
|
||
of mark(p), restores the heap pointer to its old value.
|
||
All the heap objects, created by calls of new between the call of
|
||
mark and the call of release, are removed and the space they used
|
||
can be reallocated.
|
||
Never use mark and release together with dispose!
|
||
.sp
|
||
.in -10
|
||
.ti -3
|
||
4.~\
|
||
UNIX interfacing.
|
||
.sp
|
||
If the c-option is turned on, then some special features are available
|
||
to simplify an interface with the UNIX environment.
|
||
First of all, the compiler allows you to use a different type
|
||
of string constants.
|
||
These string constants are delimited by double quotes ('"').
|
||
To put a double quote into these strings, you must repeat the double quote,
|
||
like the single quote in normal string constants.
|
||
These special string constants are terminated by a zero byte (chr(0)).
|
||
The type of these constants is a pointer to a packed array of characters,
|
||
with lower bound 1 and unknown upper bound.
|
||
.br
|
||
Secondly, the compiler predefines a new type identifier 'string' denoting
|
||
this just described string type.
|
||
.PP
|
||
The only thing you can do with these features is declaration of
|
||
constants and variables of type 'string'.
|
||
String objects may not be allocated on the heap and string pointers
|
||
may not be de-referenced.
|
||
Still these strings are very useful in combination with external routines.
|
||
The procedure write is extended to print these zero-terminated strings correctly.
|
||
.sp
|
||
.ti -3
|
||
5.~\
|
||
Double length (32 bit) integers.
|
||
.sp
|
||
If the d-option is turned on, then the additional type 'long' is known to the compiler.
|
||
Long variables have integer values in the range -2147483647..+2147483647.
|
||
Long constants may be declared.
|
||
It is not allowed to form subranges of type long.
|
||
All operations allowed on integers are also
|
||
allowed on longs and are indicated by the same
|
||
operators: '+', '-', '*', '/', 'div', 'mod'.
|
||
The procedures read and write have been extended to handle long arguments correctly.
|
||
The default width for longs is 11.
|
||
The standard procedures 'abs' and 'sqr' have been extended to work on long arguments.
|
||
Conversion from integer to long, long to real,
|
||
real to long and long to integer are automatic, like the conversion from integer to real.
|
||
These conversions may cause a
|
||
.IS
|
||
conversion error, trap 10, non-fatal
|
||
.IE
|
||
This last error is only detected in implementation 1, with 'test on'.
|
||
Note that all current implementations use target
|
||
machine floating point instructions
|
||
to perform some of the long operations.
|
||
.sp
|
||
.ti -3
|
||
6.~\
|
||
Underscore as letter.
|
||
.sp
|
||
The character '_' may be used in forming identifiers, if the u-option is turned on.
|
||
.sp
|
||
.ti -3
|
||
7.~\
|
||
Zero field width in write.
|
||
.sp
|
||
Zero or negative TotalWidth arguments to write
|
||
are allowed.
|
||
No characters are written for character, string or Boolean type arguments then.
|
||
A zero or negative FracDigits argument for fixed-point representation of reals causes the
|
||
fraction and the character '.' to be suppressed.
|
||
.sp
|
||
.ti -3
|
||
8.~\
|
||
Alternate symbol representation.
|
||
.sp
|
||
The comment delimiters '(*' and '*)' are recognized and treated like '{' and '}'.
|
||
The other alternate representations of symbols are not recognized.
|
||
.sp
|
||
.ti -3
|
||
9.~\
|
||
Pre-processing.
|
||
.sp
|
||
If the very first character of a file containing a Pascal
|
||
program is the sharp ('#', ASCII 23(hex)) the file is preprocessed
|
||
in the same way as C programs.
|
||
Lines beginning with a '#' are taken as preprocessor command lines
|
||
and not fed to the Pascal compiler proper.
|
||
C style comments, /*......*/, are removed by the C preprocessor,
|
||
thus C comments inside Pascal programs are also removed when they
|
||
are fed through the preprocessor.
|
||
.CH "Deviations from the standard"
|
||
Ack-Pascal deviates from the (March 1980) standard proposal in the following ways:
|
||
.IS
|
||
.ti -3
|
||
1.~\
|
||
Only the first 8 characters of identifiers are significant,
|
||
as requested by all standard proposals prior to March 1980.
|
||
In that proposal, however, the sentence
|
||
.DS
|
||
"A conforming program should not have its meaning altered
|
||
by the truncation of its identifiers to eight characters
|
||
or the truncation of its labels to four digits."
|
||
.DE
|
||
is missing.
|
||
.sp
|
||
.ti -3
|
||
2.~\
|
||
The character sequences 'procedur', 'procedur8', 'functionXyZ' etc. are
|
||
all erroneously classified as the word-symbols 'procedure' and 'function'.
|
||
.sp
|
||
.ti -3
|
||
3.~\
|
||
Standard procedures and functions are not allowed as parameters in Ack-Pascal,
|
||
conforming to all previous standard proposals.
|
||
You can obtain the same result with negligible loss of performance
|
||
by declaring some user routines like:
|
||
.EQ
|
||
function sine(x:real):real;
|
||
begin
|
||
sine:=sin(x)
|
||
end;
|
||
.EN
|
||
.sp
|
||
.ti -3
|
||
4.~\
|
||
The scope of identifiers and labels should start at the beginning of the block
|
||
in which these identifiers or labels are declared.
|
||
The Ack-Pascal compiler, as most other one pass compilers, deviates in this respect,
|
||
because the scope of variables and labels start
|
||
at their defining-point.
|
||
.CH "Compiler options"
|
||
Some options of the compiler may be controlled by using "{$....}".
|
||
Each option consists of a lower case letter followed by +, - or an unsigned
|
||
number.
|
||
Options are separated by commas.
|
||
The following options exist:
|
||
.in 8
|
||
.sp
|
||
.ti -8
|
||
a~+/-~~~\
|
||
this option switches assertions on and off.
|
||
If this option is on, then code is included to test these assertions
|
||
at run time. Default +.
|
||
.sp
|
||
.ti -8
|
||
c~+/-~~~\
|
||
this option, if on, allows you to use C-type string constants
|
||
surrounded by double quotes.
|
||
Moreover, a new type identifier 'string' is predefined.
|
||
Default -.
|
||
.sp
|
||
.ti -8
|
||
d~+/-~~~\
|
||
this option, if on, allows you to use variables of type 'long'.
|
||
Default -.
|
||
.sp
|
||
.ti -8
|
||
f~<num>~\
|
||
the size of reals can be changed by this option. <num> should be specified in 8-bit bytes.
|
||
The default in most implementations is 8, but other values can
|
||
occur.
|
||
.sp
|
||
.ti -8
|
||
i~<num>~\
|
||
with this flag the setsize for a set of integers can be
|
||
manipulated.
|
||
The number must be the number of bits per set.
|
||
The default value is 16, just fitting in one word on the PDP and many other minis.
|
||
.sp
|
||
.ti -8
|
||
l~+/-~~~\
|
||
if + then code is inserted to keep track of the source line number.
|
||
When this flag is switched on and off, an incorrect line number may appear
|
||
if the error occurs in a part of your program for which this flag is off.
|
||
These same line numbers are used for the profile, flow and count options
|
||
of the EM interpreter em [6].
|
||
Default +.
|
||
.sp
|
||
.ti -8
|
||
p~<num>~the size of pointers can be changed by this option. <num> should be specified in bytes.
|
||
Default 2 in most implementations.
|
||
.sp
|
||
.ti -8
|
||
r~+/-~~~\
|
||
if + then code is inserted to check subrange variables against
|
||
lower and upper subrange limits.
|
||
Default +.
|
||
.sp
|
||
.ti -8
|
||
s~+/-~~~\
|
||
if + then the compiler will hunt for places in your program
|
||
where non-standard features are used, and for each place found
|
||
it will generate a warning. Default -.
|
||
.sp
|
||
.ti -8
|
||
t~+/-~~~\
|
||
if + then each time a procedure is entered, the routine 'procentry'
|
||
is called.
|
||
The compiler checks this flag just before the first symbol that follows the
|
||
first 'begin' of the body of the procedure.
|
||
Also, when the procedure exits, then the procedure 'procexit' is called
|
||
if the t flag is on just before the last 'end' of the procedure body.
|
||
Both 'procentry' and 'procexit' have a packed array of 8 characters as a parameter.
|
||
Default procedures are present in the run time library.
|
||
Default -.
|
||
.sp
|
||
.ti -8
|
||
u~+/-~~~\
|
||
if + then the character '_' is treated like a lower case letter,
|
||
so that it may be used in identifiers.
|
||
Procedure and function identifiers starting with an underscore may cause problems,
|
||
because they may collide with library routine names.
|
||
Default -.
|
||
.in 0
|
||
.sp
|
||
Seven of these flags (c, d, f, i, p, s and u) are only effective when they appear
|
||
before the 'program' symbol. The others may be switched on and off.
|
||
.PP
|
||
A second method of passing options to the compiler ia available.
|
||
This method uses the file on which the compact EM code will be written.
|
||
The compiler starts reading from this file scanning for options
|
||
in the same format as used normally, except for the comment delimiters and
|
||
the dollar sign.
|
||
All options found on the file override the options set in your program.
|
||
Note that the compact code file must always exist before the compiler is called.
|
||
.PP
|
||
The user interface program \fIack\fP[4]
|
||
takes care of creating this file normally
|
||
and also writes one of its options onto this file.
|
||
The user can specify, for instance, without changing any character in its
|
||
Pascal program, that the compiler must include code for
|
||
procedure/function tracing.
|
||
.PP
|
||
Another very powerful debugging tool is the knowledge that inaccessible
|
||
statements and useless tests are removed by the EM optimizer.
|
||
For instance, a statement like:
|
||
.sp
|
||
.nf
|
||
if debug then
|
||
writeln('initialization done');
|
||
.fi
|
||
.sp
|
||
is completely removed by the optimizer if debug is a constant with
|
||
value false.
|
||
The first line is removed if debug is a constant with value true.
|
||
Of course, if debug is a variable nothing can be removed.
|
||
.PP
|
||
A disadvantage of Pascal, the lack of preinitialized data, can be
|
||
diminished by making use of the possibilities of the EM optimizer.
|
||
For instance, initializing an array of reserved words is sometimes
|
||
optimized into 3 EM instructions. To maximize this effect you must initialize
|
||
variables as much as possible in order of declaration and array entries
|
||
in order of decreasing index.
|
||
.CH "References"
|
||
.in +5
|
||
.ti -5
|
||
[1]~~\
|
||
ISO standard proposal ISO/TC97/SC5-N462, dated February 1979.
|
||
The same proposal, in slightly modified form, can be found in:
|
||
A.M.Addyman e.a., "A draft description of Pascal",
|
||
Software, practice and experience, May 1979.
|
||
An improved version, received March 1980,
|
||
is followed as much as possible for the
|
||
current Ack-Pascal.
|
||
.sp
|
||
.ti -5
|
||
[2]~~\
|
||
A.S.Tanenbaum, J.W.Stevenson, Hans van Staveren, E.G.Keizer,
|
||
"Description of a machine architecture for use with block structured languages",
|
||
Informatica rapport IR-81.
|
||
.sp
|
||
.ti -5
|
||
[3]~~\
|
||
W.S.Brown, S.I.Feldman, "Environment parameters and basic functions
|
||
for floating-point computation",
|
||
Bell Laboratories CSTR #72.
|
||
.sp
|
||
.ti -5
|
||
[4]~~\
|
||
UNIX manual ack(I).
|
||
.sp
|
||
.ti -5
|
||
[5]~~\
|
||
UNIX manual ld(I).
|
||
.sp
|
||
.ti -5
|
||
[6]~~\
|
||
UNIX manual em(I).
|
||
.sp
|
||
.ti -5
|
||
[7]~~\
|
||
UNIX manual libpc(VII)
|
||
.sp
|
||
.ti -5
|
||
[8]~~\
|
||
UNIX manual pc_prlib(VII)
|