2091 lines
63 KiB
Groff
2091 lines
63 KiB
Groff
.TH ACK 7
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.SH NAME
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ACK \- Additional information on the Amsterdam Compiler Kit compilers
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.SH DESCRIPTION
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.de SP
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.if t .sp 0.4
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.if n .sp
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..
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.de XS
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.SP
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.in +.5i
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.nf
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..
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.de XE
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.fi
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.in -.5i
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.SP
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..
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.de NS
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.PP
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.B ANS\ \\$1
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..
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.de UX
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\s-2UNIX\s+2
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..
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.de MX
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.if n MINIX 3
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.if t \s-1MINIX 3\s-1
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..
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.if n .ds Mx MINIX 3
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.if t .ds Mx \s-1MINIX 3\s-1
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.if n .ds Mp Minix-PC
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.if t .ds Mx \s-2MINIX-PC\s+2
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.if n .ds Mv Minix-vmd
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.if t .ds Mv \s-1MINIX 3\s-1-vmd
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.if n .ds Cw \fR
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.if t .ds Cw \fC
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.de CW
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.if n .ft R
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.if t .ft C
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..
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.\"
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These are the details on the Amsterdam Compiler Kit compilers for the
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languages C, Modula-2, and Pascal. The design decisions that were made
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where the respective standards allowed or mandated this, and the extensions
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that were implemented.
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.SH "ANSI C REPORT"
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This section specifies the implementation-defined behavior of the ANSI-C
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compiler as required by ANS X3.159-1989.
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.NS A.6.3.1
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.IP \(bu
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Diagnostics are placed on the standard error output. They have the
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following specification:
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.XS
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"<file>", line <nr>: [(<class>)] <diagnostic>
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.XE
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There are three classes of diagnostics: 'error', 'strict' and 'warning'.
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When the class is 'error', the class specification is absent.
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The class 'strict' is used for violations of the standard which are
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not severe enough to stop compilation, for example the occurrence
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of non white-space after an '#endif' preprocessing
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directive. The class 'warning' is used for legal but dubious
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constructions, for example the declaration of a structure-tag in a
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parameter type list.
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.NS A.6.3.2
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.IP \(bu
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The function 'main' can have zero or two parameters. When it has two
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parameters, the first parameter is an integer specifying the number of
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arguments on the command line (including the command). The second
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parameter is a pointer to an array of pointers to the arguments
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(as strings).
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.IP \(bu
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Interactive devices are terminals.
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.NS A.6.3.3
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.IP \(bu
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The number of significant characters is 64.
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Corresponding upper-case and lower-case letters are different.
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.NS A.6.3.4
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.IP \(bu
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The compiler assumes ASCII-characters in both the source and execution
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character set.
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.IP \(bu
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There are no multibyte characters.
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.IP \(bu
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There are 8 bits in a character.
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.IP \(bu
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Character constants that cannot be represented in 8 bits
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are truncated.
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.IP \(bu
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Character constants that are more than 1 character wide will have the
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first character specified in the least significant byte.
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.IP \(bu
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The only supported locale is 'C'.
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.IP \(bu
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A plain 'char' has the same range of values as 'signed char'.
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.NS A.6.3.5
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.IP \(bu
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The i80x86 and 68000 both have a two's complement binary-number system.
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Shorts are 2 bytes; ints are 2 bytes under 16-bits \*(Mp and 68000 \*(Mx, 4
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bytes under 32-bits \*(Mp; longs occupy 4 bytes.
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.IP \(bu
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Converting an integer to a shorter signed integer is implemented by
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ignoring the high-order byte(s) of the former.
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Converting a unsigned integer to a signed integer of the same type is
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only done in administration. This means that the bit-pattern remains
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unchanged.
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.IP \(bu
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The result of bitwise operations on signed integers are what can be
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expected on a two's complement machine.
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.IP \(bu
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When either operand is negative, the result of the / operator is the
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largest integer less than or equal to the algebraic quotient.
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The sign of the remainder on integer division is the sign of the
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enumerator.
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.IP \(bu
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The right-shift of a negative value is negative.
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.NS A.6.3.6
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.IP \(bu
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The compiler uses IEEE format for floating-point numbers.
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High-precision floating-point is used for constant folding.
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.IP \(bu
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Truncation is done to the nearest floating-point number that can
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be represented.
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.NS A.6.3.7
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.IP \(bu
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The type of the sizeof-operator (also known as size_t) is 'unsigned int'.
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.IP \(bu
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Casting an integer to a pointer or vice versa has no effect in
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bit-pattern when the sizes are equal. Otherwise the value will be
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truncated or zero-extended (depending on the direction of the
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conversion and the relative sizes).
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.IP \(bu
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The type of a 'ptrdiff_t' is 'int' on \*(Mp, and 'long' on the 68000
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\*(Mx versions.
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.NS A.6.3.8
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.IP \(bu
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Since the front end has only limited control over the registers, it can
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only make it more likely that variables that are declared as
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|
registers also end up in registers. The only things that can possibly be
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put into registers are plain ints and pointers.
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.NS A.6.3.9
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.IP \(bu
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When a member of a union object is accessed using a member of a
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different type, the resulting value will usually be garbage. The
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compiler makes no effort to catch these errors.
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.IP \(bu
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The alignment of types under 16-bit \*(Mp is 1 byte for characters and 2
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bytes for all other types. Under other MINIX 3 versions 'int' and smaller
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types are aligned to a multiple of their size, bigger scalar types are
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aligned like 'int'. Arrays have the same alignment as their elements;
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structs and unions are aligned like their field with the worst alignment.
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.IP \(bu
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A plain 'int' bit-field is taken as a 'signed int'. This means that
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a field with a size 1 bit-field can only store the values 0 and \(mi1.
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.IP \(bu
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In bit-fields, high-order bits are allocated first.
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.IP \(bu
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An enum has the same size as a plain 'int'.
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.NS A.6.3.10
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.IP \(bu
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An access to a volatile object is either a load or a store. Just
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mentioning a volatile variable is not enough.
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E.g. the statement 'x;' where x is declared volatile, does not
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constitute an access. When a volatile object should be read, but its
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value ignored, 'if (x);' should do the trick.
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.NS A.6.3.11
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.IP \(bu
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There is no fixed limit on the number of declarators that may modify an
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arithmetic, structure or union type, although specifying too many may
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cause the compiler to run out of memory.
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.NS A.6.3.12
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.IP \(bu
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The maximum number of cases in a switch-statement is in the order of
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1e9, although the compiler may run out of memory somewhat earlier.
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.NS A.6.3.13
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.IP \(bu
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Since both the preprocessor and the compiler assume ASCII-characters,
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a single character constant in a conditional-inclusion directive
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matches the same value in the execution character set.
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.IP \(bu
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The preprocessor recognizes \fI\(enI...\fR command-line options. The
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directories thus specified are searched first. After that, /usr/include is
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visited.
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.IP \(bu
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Quoted names are first looked for in the directory in which the file
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which does the include resides.
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.IP \(bu
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The characters in a h- or q- char-sequence are taken to be
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.UX
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paths.
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.IP \(bu
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Neither the front-end nor the preprocessor know any pragmas.
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.IP \(bu
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Since the compiler runs on
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.MX ,
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_\^_DATE_\^_ and _\^_TIME_\^_ will always be
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|
defined.
|
|
.NS A.6.3.14
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.IP \(bu
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NULL is defined as ((void *)0). This in order to detect dubious
|
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constructions like 'int x = NULL;'.
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.IP \(bu
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The diagnostic printed by 'assert' is as follows:
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.XS
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Assertion "<expr>" failed, file "<file>", line <line>
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.XE
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|
where <expr> is the argument to the assert macro, printed as string.
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|
(the <file> and <line> should be clear)
|
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.IP \(bu
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The sets for character test macros for the C locale are as follows:
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.XS
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.ta +\w'isalnum 'u
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\fBName Set\fR
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\fIisalnum\fR 0-9A-Za-z
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\fIisalpha\fR A-Za-z
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\fIiscntrl\fR \e000-\e037\e177
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\fIislower\fR a-z
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\fIisupper\fR A-Z
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\fIisprint\fR \e040-\e176
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.DT
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.XE
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As an addition, there is an \fIisascii\fR macro, which tests whether a character
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is an ASCII character. Characters in the range from \e000 to \e177 are ASCII
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characters.
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.IP \(bu
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The behavior of ACK mathematical functions on domain error is as follows:
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.XS
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.ta +\w'log10 'u
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\fBName Returns\fR
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\fIasin\fR 0.0
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\fIacos\fR 0.0
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\fIatan2\fR 0.0
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\fIfmod\fR 0.0
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\fIlog\fR \(miHUGE_VAL
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\fIlog10\fR \(miHUGE_VAL
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\fIpow\fR 0.0
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\fIsqrt\fR 0.0
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.DT
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.XE
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\*(Mv uses the BSD4.4 C library and the Sun FDLIBM C math library instead
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of the ACK library. See
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.BR math (3)
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for details about the math functions. The \*(Mv libraries offer at
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least the same functionality as the ACK library.
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.IP \(bu
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Underflow range errors do not cause \fIerrno\fR to be set.
|
|
.IP \(bu
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The function \fIfmod\fR returns 0.0 and sets \fIerrno\fR to EDOM when the second
|
|
argument is 0.0.
|
|
.IP \(bu
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|
The set of signals for the \fIsignal\fR function is as described by
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.BR sigaction (2).
|
|
.IP \(bu
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|
A text-stream need not end in a new-line character.
|
|
.IP \(bu
|
|
White space characters before a new-line appear when read in.
|
|
.IP \(bu
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|
There may be any number of null characters appended to a binary
|
|
stream.
|
|
.IP \(bu
|
|
The file position indicator of an append mode stream is initially
|
|
positioned at the beginning of the file.
|
|
.IP \(bu
|
|
A write on a text stream does not cause the associated file to be
|
|
truncated beyond that point.
|
|
.IP \(bu
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|
The buffering intended by the standard is fully supported.
|
|
.IP \(bu
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|
A zero-length file actually exists.
|
|
.IP \(bu
|
|
A file name can consist of any character, except for the '\e0' and
|
|
the '/'.
|
|
.IP \(bu
|
|
A file can be open multiple times.
|
|
.IP \(bu
|
|
When a \fIremove\fR is done on an open file, reading and writing behave
|
|
just as can be expected from a non-removed file. When the associated
|
|
stream is closed, however, all written data will be lost.
|
|
.IP \(bu
|
|
When a file exists prior to a call to \fIrename\fR, it is removed.
|
|
.IP \(bu
|
|
The %p conversion in \fIfprintf\fR has the same effect as %#x on \*(Mp and
|
|
%#lx on the 68000 versions of \*(Mx.
|
|
.IP \(bu
|
|
The %p conversion in \fIfscanf\fR has the same effect as %x on \*(Mp and
|
|
%lx on the 68000 versions of \*(Mx.
|
|
.IP \(bu
|
|
A \(mi character that is neither the first nor the last character in the
|
|
scanlist for %[ conversion is taken to be a range indicator. When the
|
|
first character has a higher ASCII-value than the second, the \(mi will
|
|
just be put into the scanlist.
|
|
.IP \(bu
|
|
The value of \fIerrno\fR when \fIfgetpos\fR or \fIftell\fR failed is that of \fIlseek\fR.
|
|
This means:
|
|
.XS
|
|
.ta +\w'ESPIPE 'u +\w'\- 'u
|
|
EBADF \- when the stream is not valid
|
|
ESPIPE \- when fildes is associated with a pipe
|
|
EINVAL \- the resulting file pointer would be negative
|
|
.XE
|
|
.IP \(bu
|
|
The messages generated by \fIperror\fR depend on the value of \fIerrno\fR.
|
|
The mapping of errors to strings is done by \fIstrerror\fR.
|
|
.IP \(bu
|
|
When the requested size is zero, \fImalloc\fR, \fIcalloc\fR and \fIrealloc\fR
|
|
return a null-pointer under \*(Mx. Under \*(Mv a unique non-null pointer is
|
|
returned.
|
|
.IP \(bu
|
|
When \fIabort\fR is called, output buffers will be flushed. Temporary files
|
|
(made with the \fItmpfile\fR function) will have disappeared when SIGABRT
|
|
is not caught or ignored.
|
|
.IP \(bu
|
|
The \fIexit\fR function returns the low-order eight bits of its argument
|
|
to the environment.
|
|
.IP \(bu
|
|
The predefined environment names are controlled by the user.
|
|
Setting environment variables is done through the \fIputenv\fR function.
|
|
This function accepts a pointer to char as its argument.
|
|
To set, for example, the environment variable TERM to a230 one writes
|
|
.XS
|
|
static char terminal[] = "TERM=a230";
|
|
putenv(terminal);
|
|
.XE
|
|
The argument to \fIputenv\fR is stored in an internal table, so malloc'ed
|
|
strings cannot be freed until another call to \fIputenv\fR (which sets the
|
|
same environment variable) is made. The argument to \fIputenv\fR must be
|
|
writable, which means that officially, the argument cannot be a string
|
|
constant.
|
|
The function returns 1 if it fails, 0 otherwise.
|
|
.LP
|
|
.IP \(bu
|
|
The argument to \fIsystem\fR is passed as argument to \fI/bin/sh \(enc\fR.
|
|
.IP \(bu
|
|
The strings returned by \fIstrerror\fR depend on \fIerrno\fR. They are
|
|
listed in
|
|
.BR intro (2).
|
|
Everything else causes \fIstrerror\fR to return "unknown error" under \*(Mx,
|
|
or the result of sprintf("Error %d", errno) under \*(Mv.
|
|
.IP \(bu
|
|
The local time zone is per default GMT. This can be
|
|
changed through the TZ environment variable, e.g. TZ=EST6.
|
|
See
|
|
.BR TZ (5).
|
|
.IP \(bu
|
|
The \fIclock\fR function returns the number of ticks since process
|
|
startup.
|
|
.SS References
|
|
.IP [1]
|
|
ANS X3.159-1989
|
|
.ft I
|
|
American National Standard for Information Systems -
|
|
Programming Language C
|
|
.ft R
|
|
.SH "THE MINIX MODULA-2 COMPILER"
|
|
This section describes the implementation-specific features of the
|
|
.MX
|
|
Modula-2 compiler.
|
|
It is not intended to teach Modula-2 programming.
|
|
For a description of the Modula-2 language,
|
|
the reader is referred to [1].
|
|
.SS "The language implemented"
|
|
.PP
|
|
This paragraph discusses the deviations from the Modula-2 language as described
|
|
in the 'Report on The Programming Language Modula-2',
|
|
as it appeared in [1],
|
|
from now on referred to as 'the Report'.
|
|
Also,
|
|
the Report sometimes leaves room for interpretation.
|
|
The section numbers
|
|
mentioned are the section numbers of the Report.
|
|
.SS "Syntax (section 2)"
|
|
.PP
|
|
The syntax recognized is that of the Report,
|
|
with some extensions to
|
|
also recognize the syntax of an earlier definition,
|
|
given in [2].
|
|
Only one compilation unit per file is accepted.
|
|
.SS "Vocabulary and Representation (section 3)"
|
|
.PP
|
|
The input '\*(Cw10..\fR' is parsed as two tokens: '\*(Cw10\fR' and '\*(Cw..\fR'.
|
|
.PP
|
|
The empty string \*(Cw""\fR has type
|
|
.XS
|
|
.CW
|
|
ARRAY [0 .. 0] OF CHAR
|
|
.ft P
|
|
.XE
|
|
and contains one character: \*(Cw0C\fR.
|
|
.PP
|
|
When the text of a comment starts with a '\*(Cw$\fR',
|
|
it may be a pragma.
|
|
Currently,
|
|
the following pragmas exist:
|
|
.nf
|
|
.SP
|
|
.CW
|
|
(*$F (F stands for Foreign) *)
|
|
(*$R[+|-] (Runtime checks, on or off, default on) *)
|
|
(*$A[+|-] (Array bound checks, on or off, default off) *)
|
|
(*$U (Allow for underscores within identifiers) *)
|
|
.ft P
|
|
.SP
|
|
.fi
|
|
The Foreign pragma is only meaningful in a \*(CwDEFINITION MODULE\fR,
|
|
and indicates that this
|
|
\*(CwDEFINITION MODULE\fR describes an interface to a module written in another
|
|
language (for instance C or Pascal).
|
|
Runtime checks that can be disabled are:
|
|
range checks,
|
|
\*(CwCARDINAL\fR overflow checks,
|
|
checks when assigning a \*(CwCARDINAL\fR to an \*(CwINTEGER\fR and vice versa,
|
|
and checks that \*(CwFOR\fR-loop control-variables are not changed
|
|
in the body of the loop.
|
|
Array bound checks can be enabled,
|
|
because many EM implementations do not
|
|
implement the array bound checking of the EM array instructions.
|
|
When enabled,
|
|
the compiler generates a check before generating an
|
|
EM array instruction.
|
|
Even when underscores are enabled,
|
|
they still may not start an identifier.
|
|
.PP
|
|
Constants of type \*(CwLONGINT\fR are integers with a suffix letter \*(CwD\fR
|
|
(for instance \*(Cw1987D\fR).
|
|
Constants of type \*(CwLONGREAL\fR have suffix \*(CwD\fR if a scale factor is missing,
|
|
or have \*(CwD\fR in place of \*(CwE\fR in the scale factor (f.i. \*(Cw1.0D\fR,
|
|
\*(Cw0.314D1\fR).
|
|
This addition was made,
|
|
because there was no way to indicate long constants,
|
|
and also because the addition was made in Wirth's newest Modula-2 compiler.
|
|
.SS "Declarations and scope rules (section 4)"
|
|
.PP
|
|
Standard identifiers are predeclared,
|
|
and valid in all
|
|
parts of a program.
|
|
They are called \fIpervasive\fR.
|
|
Unfortunately,
|
|
the Report does not state how this pervasiveness is accomplished.
|
|
However,
|
|
page 87 of [1] states: 'Standard identifiers are automatically
|
|
imported into all modules'.
|
|
Our implementation therefore allows
|
|
redeclarations of standard identifiers within procedures,
|
|
but not within
|
|
modules.
|
|
.SS "Constant expressions (section 5)"
|
|
.PP
|
|
Each operand of a constant expression must be a constant:
|
|
a string,
|
|
a number,
|
|
a set,
|
|
an enumeration literal,
|
|
a qualifier denoting a
|
|
constant expression,
|
|
a type transfer with a constant argument,
|
|
or one of the standard procedures
|
|
\*(CwABS\fR,
|
|
\*(CwCAP\fR,
|
|
\*(CwCHR\fR,
|
|
\*(CwLONG\fR,
|
|
\*(CwMAX\fR,
|
|
\*(CwMIN\fR,
|
|
\*(CwODD\fR,
|
|
\*(CwORD\fR,
|
|
\*(CwSIZE\fR,
|
|
\*(CwSHORT\fR,
|
|
\*(CwTSIZE\fR,
|
|
or \*(CwVAL\fR,
|
|
with constant argument(s);
|
|
\*(CwTSIZE\fR and \*(CwSIZE\fR may also have a variable as argument.
|
|
.SS "Type declarations (section 6)"
|
|
.LP
|
|
.ft I
|
|
1. Basic types (section 6.1)
|
|
.PP
|
|
The type \*(CwCHAR\fR includes the ASCII character set as a subset.
|
|
Values range from
|
|
\*(Cw0C\fR to \*(Cw377C\fR,
|
|
not from \*(Cw0C\fR to \*(Cw177C\fR.
|
|
.LP
|
|
.ft I
|
|
2. Enumerations (section 6.2)
|
|
.PP
|
|
The maximum number of enumeration literals in any one enumeration type
|
|
is \*(CwMAX(INTEGER)\fR.
|
|
.LP
|
|
.ft I
|
|
3. Record types (section 6.5)
|
|
.PP
|
|
The syntax of variant sections in [1] is different from the one in [2].
|
|
Our implementation recognizes both,
|
|
giving a warning for the older one.
|
|
.LP
|
|
.ft I
|
|
4. Set types (section 6.6)
|
|
.PP
|
|
The only limitation imposed by the compiler is that the base type of the
|
|
set must be a subrange type,
|
|
an enumeration type,
|
|
\*(CwCHAR\fR,
|
|
or \*(CwBOOLEAN\fR.
|
|
So,
|
|
the lower bound may be negative.
|
|
However,
|
|
if a negative lower bound is used,
|
|
the compiler gives a warning of the \fIrestricted\fR class.
|
|
.PP
|
|
The standard type \*(CwBITSET\fR is defined as
|
|
.XS
|
|
.CW
|
|
TYPE BITSET = SET OF [0 .. 8*SIZE(INTEGER)-1];
|
|
.ft P
|
|
.XE
|
|
.SS "Expressions (section 8)"
|
|
.LP
|
|
.ft I
|
|
1. Operators (section 8.2)
|
|
.LP
|
|
.ft I
|
|
1.1. Arithmetic operators (section 8.2.1)
|
|
.PP
|
|
The Report does not specify the priority of the unary
|
|
operators \*(Cw+\fR or \*(Cw-\fR:
|
|
It does not specify whether
|
|
.XS
|
|
.CW
|
|
- 1 + 1
|
|
.ft P
|
|
.XE
|
|
means
|
|
.XS
|
|
.CW
|
|
- (1 + 1)
|
|
.ft P
|
|
.XE
|
|
or
|
|
.XS
|
|
.CW
|
|
(-1) + 1
|
|
.ft P
|
|
.XE
|
|
The
|
|
.MX
|
|
Modula-2 compiler implements the second alternative.
|
|
.SS "Statements (section 9)"
|
|
.LP
|
|
.ft I
|
|
1. Assignments (section 9.1)
|
|
.PP
|
|
The Report does not define the evaluation order in an assignment.
|
|
Our compiler certainly chooses an evaluation order,
|
|
but it is explicitly left undefined.
|
|
Therefore,
|
|
programs that depend on it may cease to work later.
|
|
.PP
|
|
The types \*(CwINTEGER\fR and \*(CwCARDINAL\fR are assignment-compatible with
|
|
\*(CwLONGINT\fR,
|
|
and \*(CwREAL\fR is assignment-compatible with \*(CwLONGREAL\fR.
|
|
.LP
|
|
.ft I
|
|
2. Case statements (section 9.5)
|
|
.PP
|
|
The size of the type of the case-expression must be less than or equal to
|
|
the word-size.
|
|
.PP
|
|
The Report does not specify what happens if the value of the case-expression
|
|
does not occur as a label of any case,
|
|
and there is no \*(CwELSE\fR-part.
|
|
In our implementation,
|
|
this results in a runtime error.
|
|
.LP
|
|
.ft I
|
|
3. For statements (section 9.8)
|
|
.PP
|
|
The Report does not specify the legal types for a control variable.
|
|
Our implementation allows the basic types (except \*(CwREAL\fR),
|
|
enumeration types,
|
|
and subranges.
|
|
A runtime warning is generated when the value of the control variable
|
|
is changed by the statement sequence that forms the body of the loop,
|
|
unless runtime checking is disabled.
|
|
.LP
|
|
.ft I
|
|
4. Return and exit statements (section 9.11)
|
|
.PP
|
|
The Report does not specify which result-types are legal.
|
|
Our implementation allows any result type.
|
|
.SS "Procedure declarations (section 10)"
|
|
.PP
|
|
Function procedures must exit through a RETURN statement,
|
|
or a runtime error occurs.
|
|
.LP
|
|
.ft I
|
|
1. Standard procedures (section 10.2)
|
|
.PP
|
|
Our implementation supports \*(CwNEW\fR and \*(CwDISPOSE\fR
|
|
for backwards compatibility,
|
|
but issues warnings for their use.
|
|
.PP
|
|
Also,
|
|
some new standard procedures were added,
|
|
similar to the new standard procedures in Wirth's newest compiler:
|
|
.IP \-
|
|
\*(CwLONG\fR converts an argument of type \*(CwINTEGER\fR or \*(CwREAL\fR to the
|
|
types \*(CwLONGINT\fR or \*(CwLONGREAL\fR.
|
|
.IP \-
|
|
\*(CwSHORT\fR performs the inverse transformation,
|
|
without range checks.
|
|
.IP \-
|
|
\*(CwFLOATD\fR is analogous to \*(CwFLOAT\fR,
|
|
but yields a result of type
|
|
\*(CwLONGREAL\fR.
|
|
.IP \-
|
|
\*(CwTRUNCD\fR is analogous to \*(CwTRUNC\fR,
|
|
but yields a result of type
|
|
\*(CwLONGINT\fR.
|
|
.SS "System-dependent facilities (section 12)"
|
|
.PP
|
|
The type \*(CwBYTE\fR is added to the \*(CwSYSTEM\fR module.
|
|
It occupies a storage unit of 8 bits.
|
|
\*(CwARRAY OF BYTE\fR has a similar effect to \*(CwARRAY OF WORD\fR,
|
|
but is safer.
|
|
In some obscure cases the \*(CwARRAY OF WORD\fR mechanism does not quite
|
|
work properly.
|
|
.PP
|
|
The procedure \*(CwIOTRANSFER\fR is not implemented.
|
|
.SS "Backwards compatibility"
|
|
.PP
|
|
Besides recognizing the language as described in [1],
|
|
the compiler recognizes most of the language described in [2],
|
|
for backwards compatibility.
|
|
It warns the user for old-fashioned
|
|
constructions (constructions that [1] does not allow).
|
|
If the \fI\(en3\fR option is passed to \fIm2\fR,
|
|
this backwards compatibility feature is disabled.
|
|
.SS "Compile time errors"
|
|
.PP
|
|
The compile time error messages are intended to be self-explanatory,
|
|
and not listed here.
|
|
The compiler also sometimes issues warnings,
|
|
recognizable by a warning-classification between parentheses.
|
|
There are 3 classifications:
|
|
.IP "(old-fashioned use)"
|
|
.br
|
|
These warnings are given on constructions that are not allowed by [1],
|
|
but are allowed by [2].
|
|
.IP (strict)
|
|
.br
|
|
These warnings are given on constructions that are supported by the
|
|
.MX
|
|
Modula-2 compiler,
|
|
but might not be supported by others.
|
|
Examples: functions returning structured types,
|
|
SET types of subranges with
|
|
negative lower bound.
|
|
.IP (warning)
|
|
.br
|
|
The other warnings,
|
|
such as warnings about variables that are never assigned,
|
|
never used,
|
|
etc.
|
|
.SS "Runtime errors"
|
|
.PP
|
|
The \fITraps\fR module enables the user to install his own runtime
|
|
error handler.
|
|
The default one just displays what happened and exits.
|
|
Basically,
|
|
a trap handler is just a procedure that takes an INTEGER as
|
|
parameter.
|
|
The INTEGER is the trap number.
|
|
This INTEGER can be one of the
|
|
EM trap numbers,
|
|
listed in [3],
|
|
or one of the numbers listed in the
|
|
\fITraps\fR definition module.
|
|
.PP
|
|
The following runtime errors may occur:
|
|
.IP "array bound error"
|
|
.br
|
|
This error is detected if the \fI\(enA\fR option is given to \fIm2\fR.
|
|
.IP "range bound error"
|
|
.br
|
|
Range bound errors are always detected,
|
|
unless runtime checks are disabled.
|
|
.IP "set bound error"
|
|
.IP "cardinal overflow"
|
|
.br
|
|
This error is detected,
|
|
unless runtime checks are disabled.
|
|
.IP "cardinal underflow"
|
|
.br
|
|
This error is detected,
|
|
unless runtime checks are disabled.
|
|
.IP "divide by 0"
|
|
.IP "divide by 0.0"
|
|
.IP "conversion error"
|
|
.br
|
|
This error occurs when assigning a negative value of type INTEGER to a
|
|
variable of type CARDINAL,
|
|
or when assigning a value of CARDINAL that is > MAX(INTEGER),
|
|
to a variable of type INTEGER.
|
|
It is detected,
|
|
unless runtime checking is disabled.
|
|
.IP "heap overflow"
|
|
.br
|
|
This might happen when ALLOCATE fails.
|
|
.IP "case error"
|
|
.br
|
|
This error occurs when non of the cases in a CASE statement are selected,
|
|
and the CASE statement has no ELSE part.
|
|
.IP "stack size of process too large"
|
|
.br
|
|
This is most likely to happen if the reserved space for a coroutine stack
|
|
is too small.
|
|
In this case,
|
|
increase the size of the area given to
|
|
\*(CwNEWPROCESS\fR.
|
|
It can also happen if the stack needed for the main
|
|
process is too large and there are coroutines.
|
|
In this case,
|
|
the only fix is to reduce the stack size needed by the main process,
|
|
f.i. by avoiding local arrays.
|
|
.IP "too many nested traps + handlers"
|
|
.br
|
|
This error can only occur when the user has installed his own trap handler.
|
|
It means that during execution of the trap handler another trap has occurred,
|
|
and that several times.
|
|
In some cases,
|
|
this is an error because of overflow of some internal tables.
|
|
.IP "no RETURN from function procedure"
|
|
.br
|
|
This error occurs when a function procedure does not return properly
|
|
('falls' through).
|
|
.IP "illegal instruction"
|
|
.br
|
|
This error might occur when you use floating point operations on an
|
|
implementation that does not have floating point.
|
|
.PP
|
|
In addition,
|
|
some of the library modules may give error messages.
|
|
The \fBTraps\fR-module has a suitable mechanism for this.
|
|
.SS "The procedure call interface"
|
|
.PP
|
|
Parameters are pushed on the stack in reversed order.
|
|
For VAR parameters,
|
|
its address is passed,
|
|
for value parameters its value.
|
|
The only exception to this rule is with conformant arrays.
|
|
For conformant arrays,
|
|
the address is passed,
|
|
and an array descriptor is
|
|
passed.
|
|
The descriptor is an EM array descriptor.
|
|
It consists of three
|
|
fields: the lower bound (always 0),
|
|
upper bound \(mi lower bound,
|
|
and the size of the elements.
|
|
The descriptor is pushed first.
|
|
If the parameter is a value parameter,
|
|
the called routine must make sure
|
|
that its value is never changed,
|
|
for instance by making its own copy
|
|
of the array.
|
|
.PP
|
|
When the size of the return value of a function procedure is larger than
|
|
the maximum of \*(CwSIZE(LONGREAL)\fR and twice the pointer-size,
|
|
the caller reserves this space on the stack,
|
|
above the parameters.
|
|
Callee then stores
|
|
its result there,
|
|
and returns no other value.
|
|
.SS "The Modula-2 runtime library"
|
|
.PP
|
|
The definition modules of the modules available in the
|
|
.MX
|
|
Modula-2 runtime library reside in the directory \fI/usr/lib/ack/m2\fR.
|
|
.SS References
|
|
.IP [1]
|
|
Niklaus Wirth,
|
|
.ft I
|
|
Programming in Modula-2, third, corrected edition,
|
|
.ft R
|
|
Springer-Verlag, Berlin (1985)
|
|
.IP [2]
|
|
Niklaus Wirth,
|
|
.ft I
|
|
Programming in Modula-2,
|
|
.ft R
|
|
Stringer-Verlag, Berlin (1983)
|
|
.IP [3]
|
|
A.S.Tanenbaum, J.W.Stevenson, Hans van Staveren, E.G.Keizer,
|
|
.ft I
|
|
Description of a machine architecture for use with block structured languages,
|
|
.ft R
|
|
Informatica rapport IR-81, Vrije Universiteit, Amsterdam
|
|
.SH "THE MINIX PASCAL COMPILER"
|
|
.PP
|
|
.de IT
|
|
.PP
|
|
.B BS\ \\$1:
|
|
..
|
|
.de IS
|
|
.PP
|
|
.in +.5i
|
|
..
|
|
.PP
|
|
This section refers to the (1982) BSI standard for Pascal [1].
|
|
.MX
|
|
Pascal complies with the requirements of level 1 of BS 6192: 1982, with
|
|
the exceptions as listed in this section.
|
|
.PP
|
|
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 section.
|
|
.SS "Implementation-defined features"
|
|
.PP
|
|
For each implementation-defined feature mentioned in the BSI standard
|
|
we give the section number, the quotation from that section and the definition.
|
|
First we quote the definition of implementation-defined:
|
|
.PP
|
|
.RS
|
|
Possibly differing between processors, but defined for any particular
|
|
processor.
|
|
.RE
|
|
.IT 6.1.7
|
|
Each string-character shall denote an implementation-defined value of the
|
|
required char-type.
|
|
.IS
|
|
All 7-bit ASCII characters except linefeed LF (10) are allowed.
|
|
.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 by the signed-real values.
|
|
.IS
|
|
The set of real values range from a low of \(mi1.7976931348623157e+308 to
|
|
a high of 1.7976931348623157e+308.
|
|
.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-bit 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.
|
|
.IT 6.6.5.2
|
|
The post-assertions imply corresponding activities on the external entities,
|
|
if any, to which the file-variables are bound.
|
|
These activities, and the
|
|
point at which they are actually performed, shall be
|
|
implementation-defined.
|
|
.IS
|
|
The reading and writing writing of objects on files is buffered.
|
|
This means that when a program terminates abnormally, I/O may be
|
|
unfinished.
|
|
Terminal I/O is unbuffered.
|
|
Files are closed whenever they are rewritten or reset, or on
|
|
program termination.
|
|
.IT 6.7.2.2
|
|
The predefined constant \fImaxint\fR shall be of integer-type and shall denote
|
|
an implementation-defined value, that satisfies the following conditions:
|
|
.IP (a)
|
|
All integral values in the closed interval from \fI\(mimaxint\fR to \fI+maxint\fR
|
|
shall be values of the integer-type.
|
|
.IP (b)
|
|
Any monadic operation performed on an integer value in this interval
|
|
shall be correctly performed according to the mathematical rules for
|
|
integer arithmetic.
|
|
.IP (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.
|
|
.IP (d)
|
|
Any relational operation on two integer values in this same interval
|
|
shall be correctly performed according to the mathematical rules for
|
|
integer arithmetic.
|
|
.SP
|
|
The representation of integers under 16-bit \*(Mp or under 68000 \*(Mx
|
|
is a 16-bit word using two's complement arithmetic. The integers range
|
|
from \(mi32768 to +32767. Under 32-bit \*(Mp a 32-bit integer is used
|
|
ranging from \(mi2147483648 to +2147483647.
|
|
.IT 6.7.2.2
|
|
The result of the real arithmetic operators and functions shall be
|
|
approximations to the corresponding mathematical results.
|
|
The accuracy of
|
|
this approximation shall be implementation-defined
|
|
.IS
|
|
The default size of reals is 8 bytes, the accuracy is 11 bits for the exponent,
|
|
and 53 bits for the mantissa.
|
|
This gives an accuracy of about 16 digits.
|
|
and exponents ranging from \(mi307 to +307.
|
|
.IT 6.9.3.1
|
|
The default TotalWidth values for integer, Boolean and real types
|
|
shall be implementation-defined.
|
|
.IS
|
|
The defaults are:
|
|
.XS
|
|
.ta +\w'Boolean 'u +\w'14 'u
|
|
integer 6 (16-bit)
|
|
integer 11 (32-bit)
|
|
Boolean 5
|
|
real 14
|
|
.DT
|
|
.XE
|
|
.IT 6.9.3.4.1
|
|
ExpDigits, the number of digits written in an exponent part of a real,
|
|
shall be implementation-defined.
|
|
.IS
|
|
ExpDigits is defined as 3.
|
|
.IT 6.9.3.4.1
|
|
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 6.9.3.5
|
|
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 6.9.5
|
|
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 the Pascal library.
|
|
.IT 6.10
|
|
The effect of an explicit use of reset or rewrite
|
|
on the standard text files input or output shall be implementation-defined.
|
|
.IS
|
|
The procedures reset and rewrite are no-ops
|
|
if applied to input or output.
|
|
.in 0
|
|
.SS "Implementation-dependent features"
|
|
.PP
|
|
For each implementation-dependent feature mentioned in the BSI standard,
|
|
we give the section number, the quotation from that section and the way
|
|
this feature is treated by the
|
|
.MX
|
|
Pascal system.
|
|
First we quote the definition of 'implementation-dependent':
|
|
.PP
|
|
.RS
|
|
Possibly differing between processors and not necessarily defined for any
|
|
particular processor.
|
|
.RE
|
|
.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
|
|
.XS
|
|
if (p<>nil) and (p^.value<>0) then
|
|
.XE
|
|
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:
|
|
.IP 1.
|
|
The modulo operation is performed by a library routine to
|
|
check for negative values of the right operand.
|
|
.IP 2.
|
|
The expression
|
|
.XS
|
|
set1 <= set2
|
|
.XE
|
|
where set1 and set2 are compatible set types is evaluated in the
|
|
following steps:
|
|
.XS
|
|
.ta +\w'\- 'u
|
|
\- evaluate set2;
|
|
\- evaluate set1;
|
|
\- compute set2+set1;
|
|
\- test set2 and set2+set1 for equality.
|
|
.DT
|
|
.XE
|
|
.IP 3.
|
|
The expression
|
|
.XS
|
|
set1 >= set2
|
|
.XE
|
|
where set1 and set2 are compatible set types is evaluated in the following steps:
|
|
.XS
|
|
.ta +\w'\- 'u
|
|
\- evaluate set1;
|
|
\- evaluate set2;
|
|
\- compute set1+set2;
|
|
\- test set1 and set1+set2 for equality.
|
|
.DT
|
|
.XE
|
|
.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
|
|
The decision as to the order of accessing the variable and evaluating
|
|
the expression in an assignment-statement, 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 6.9.5
|
|
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.
|
|
.in 0
|
|
.SS "Error handling"
|
|
.PP
|
|
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:
|
|
.PP
|
|
.RS
|
|
An error is a violation by a program of the requirements of this standard
|
|
that a processor is permitted to leave undetected.
|
|
.RE
|
|
.LP
|
|
.ft I
|
|
Compiler errors
|
|
.PP
|
|
Error are written on the standard error output.
|
|
Each line has the form:
|
|
.XS
|
|
<file>, line <number>: <description>
|
|
.XE
|
|
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
|
|
Sometimes the compiler produces several errors for the same line.
|
|
They are only shown up to a maximum of 5 errors per line.
|
|
Warning are also shown up to a maximum of 5 per line.
|
|
.PP
|
|
Extensive treatment of these errors is outside the scope of this manual.
|
|
.LP
|
|
.ft I
|
|
Runtime errors
|
|
.PP
|
|
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 \fI\(enn\fR option is turned on, the compiler generates code to keep track
|
|
of which source line causes which instructions to be generated.
|
|
.PP
|
|
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 below.
|
|
.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 errors are only detected when the 'A' option is used.
|
|
In the other cases, a range bound error occurs when the value of type T2
|
|
is not in the closed interval specified by T1, unless range checks are
|
|
disabled.
|
|
.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 6.5.3.3
|
|
It shall be an error if a component of a variant-part of a variant,
|
|
where the selector of the variant-part is not a field,
|
|
is accessed unless the variant is active for the entirety of each
|
|
reference and access to each component of the variant.
|
|
.IS
|
|
This error is not detected.
|
|
.IT 6.5.4
|
|
It shall be an error if
|
|
the pointer-variable of an identified-variable either denotes a
|
|
nil-value or is undefined.
|
|
.IS
|
|
This error is not detected.
|
|
.IT 6.5.4
|
|
It shall be an error to remove the identifying-value of an identified
|
|
variable from its pointer-type when a reference to the variable exists.
|
|
.IS
|
|
When the identified variable is an element of the record-variable-list of
|
|
a with-statement, a warning is given at compile-time.
|
|
Otherwise, this error is not detected.
|
|
.IT 6.5.5
|
|
It shall be an error to alter the value of a file-variable f when a
|
|
reference to the buffer-variable f^ exists.
|
|
.IS
|
|
When f is altered when it is an element of the record-variable-list of a
|
|
with-statement, a warning is given.
|
|
When a buffer-variable is used as a
|
|
variable-parameter, an error is given.
|
|
This is done at compile-time.
|
|
.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:
|
|
.XS
|
|
.ta +\w'rewrite(f): 'u
|
|
rewrite(f): no pre-assertion.
|
|
put(f): f is opened for writing and f^ is not undefined.
|
|
reset(f): f exists.
|
|
get(f): f is opened for reading and eof(f) is false.
|
|
.DT
|
|
.XE
|
|
The following errors are detected for these operations:
|
|
.SP
|
|
rewrite(f):
|
|
.in +6
|
|
.ti -3
|
|
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 -3
|
|
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 -6
|
|
.SP
|
|
put(f):
|
|
.in +6
|
|
.ti -3
|
|
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 -3
|
|
not writable, trap 96, fatal:
|
|
.br
|
|
f is opened for reading.
|
|
.ti -3
|
|
write error, trap 104, fatal:
|
|
.br
|
|
probably caused by file system problems.
|
|
For instance, the file storage is exhausted.
|
|
Because I/O 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 -6
|
|
.SP
|
|
reset(f):
|
|
.in +6
|
|
.ti -3
|
|
more args expected, trap 64, fatal:
|
|
.br
|
|
same as for rewrite(f).
|
|
.ti -3
|
|
reset error, trap 100, fatal:
|
|
.br
|
|
f does not exist, or the caller has insufficient access rights, or
|
|
operating system tables are exhausted.
|
|
.in -6
|
|
.SP
|
|
get(f):
|
|
.in +6
|
|
.ti -3
|
|
file not yet open, trap 72, fatal:
|
|
.br
|
|
as for put(f).
|
|
.ti -3
|
|
not readable, trap 97, fatal:
|
|
.br
|
|
f is opened for writing.
|
|
.ti -3
|
|
end of file, trap 98, fatal:
|
|
.br
|
|
eof(f) is true just before the call to get(f).
|
|
.ti -3
|
|
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 -3
|
|
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 -3
|
|
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 -6
|
|
.IT 6.6.5.3
|
|
It shall be an error if a variant of a variant-part within the new
|
|
variable becomes active and a different variant of the variant-part is
|
|
one of the specified variants.
|
|
.IS
|
|
This error is not detected.
|
|
.IT 6.6.5.3
|
|
It shall be an error to use dispose(q) if the identifying variable has been
|
|
allocated using the form new(p,c1,...,cn).
|
|
.IS
|
|
This error is not detected.
|
|
However, 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 to use dispose(q,k1,...,km) if the identifying
|
|
variable has been allocated using the form new(p,c1,...,cn) and m is not
|
|
equal to n.
|
|
.IS
|
|
This error is not detected.
|
|
However, 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
|
|
This error is detected for nil-value (dispose error, trap 73, fatal).
|
|
.IT 6.6.5.3
|
|
It shall be an error if a variable created using the second form of new is
|
|
accessed by the identified variable of the variable-access of a factor,
|
|
of an assignment-statement, or of an actual-parameter.
|
|
.IS
|
|
This error is not detected.
|
|
.IT 6.6.6.2
|
|
It shall be an error if the value of sqr(x) does not exist.
|
|
.IS
|
|
This error is detected for real-type arguments (real overflow,
|
|
trap 4, non-fatal).
|
|
.IT 6.6.6.2
|
|
It shall be an error if x in ln(x) is smaller than or equal to 0.
|
|
.IS
|
|
This error is detected (error in ln, trap 66, non-fatal)
|
|
.IT 6.6.6.2
|
|
It shall be an error if x in sqrt(x) is smaller than 0.
|
|
.IS
|
|
This error is detected (error in sqrt, trap 67, non-fatal)
|
|
.SP
|
|
In addition to these errors, overflow in the expression exp(x) is
|
|
detected (error in exp, trap 65, non-fatal; real overflow, trap 4, non-fatal)
|
|
.IT 6.6.6.3
|
|
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 6.6.6.3
|
|
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 6.6.6.4
|
|
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 6.6.6.4
|
|
It shall be an error if
|
|
the character value of chr(x) does not exist.
|
|
.IS
|
|
This error is detected (range bound error, trap 1, non-fatal).
|
|
.IT 6.6.6.4
|
|
It shall be an error if the value of succ(x) does not exist.
|
|
.IS
|
|
Same comments as for chr(x).
|
|
.IT 6.6.6.4
|
|
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.
|
|
.IT 6.7.1
|
|
It shall be an error if a variable-access used as an operand
|
|
in an expression is undefined at the time of its use.
|
|
.IS
|
|
The compiler performs some limited checks to see if identifiers are
|
|
used before they are set.
|
|
Since it can not always be sure (one could, for
|
|
instance, jump out of a loop), only a warning is generated.
|
|
When an
|
|
expression contains a function-call, an error occurs if the
|
|
function is not assigned at run-time.
|
|
.IT 6.7.2.2
|
|
A term of the form x/y shall be an error if y is zero.
|
|
.IS
|
|
This error is detected (divide by 0.0, trap 7, non-fatal).
|
|
.IT 6.7.2.2
|
|
It shall be an error if j is zero in 'i div j'.
|
|
.IS
|
|
This error is detected (divide by 0, trap 6, non-fatal).
|
|
.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
|
|
This implementation does not detect integer overflow.
|
|
.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 6.9.1
|
|
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 6.9.1
|
|
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 6.9.1
|
|
When read is applied to f, it shall be an error if the buffer-variable f^
|
|
is undefined or the pre-assertions for get do not hold.
|
|
.IS
|
|
This error is detected (see get(f)).
|
|
.IT 6.9.3
|
|
When write is applied to a text file f, it shall be an error if f is
|
|
undefined or f is opened for reading.
|
|
.IS
|
|
This error is detected (see put(f)).
|
|
Furthermore, this error is also
|
|
detected when f is not a text file.
|
|
.IT 6.9.3.1
|
|
The values of TotalWidth or FracDigits shall be greater than or equal to
|
|
one; it shall be an error if either value is less then one.
|
|
.IS
|
|
When either value is less than zero, an error (illegal field width, trap
|
|
75, non-fatal) occurs.
|
|
Zero values are allowed, in order to maintain some
|
|
compatibility with the old
|
|
.MX
|
|
Pascal compiler.
|
|
.IT 6.9.5
|
|
It shall be an error if the pre-assertion required for writeln(f) doe not
|
|
hold prior to the invocation of page(f);
|
|
.IS
|
|
This error is detected (see put(f)).
|
|
.in 0
|
|
.SS "Extensions to the standard"
|
|
.LP
|
|
.ft I
|
|
1. External routines
|
|
.LP
|
|
Except for the required directive 'forward' the
|
|
.MX
|
|
Pascal compiler recognizes
|
|
the 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.
|
|
.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.
|
|
.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
|
|
.XS
|
|
.ta +\w'function a(pars):type 'u
|
|
\fBPascal C\fR
|
|
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 ;
|
|
}
|
|
.DT
|
|
.XE
|
|
The Pascal runtime system uses the following algorithm when calling
|
|
function/procedures passed as parameters.
|
|
.XS
|
|
if (static_link) {
|
|
(*a)(static_link, pars);
|
|
} else {
|
|
(*a)(pars);
|
|
}
|
|
.XE
|
|
.LP
|
|
.ft I
|
|
2. Separate compilation.
|
|
.LP
|
|
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
|
|
.XS
|
|
.in +\w'module = 'u
|
|
.ti -\w'module = 'u
|
|
module = [constant-definition-part]
|
|
[type-definition-part]
|
|
[var-declaration-part]
|
|
[procedure-and-function-declaration-part]
|
|
.in -\w'module = 'u
|
|
.XE
|
|
The compiler accepts a program or a module:
|
|
.XS
|
|
unit = program | module
|
|
.XE
|
|
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.
|
|
.LP
|
|
.ft I
|
|
3. Assertions.
|
|
.LP
|
|
When the s-option is off,
|
|
.MX
|
|
Pascal compiler recognizes an additional
|
|
statement, the assertion.
|
|
Assertions can be used as an aid in debugging
|
|
and documentation.
|
|
The syntax is:
|
|
.XS
|
|
assertion = 'assert' Boolean-expression
|
|
.XE
|
|
An assertion is a simple-statement, so
|
|
.XS
|
|
.in +\w'simple-statement = ['u
|
|
.ti -\w'simple-statement = ['u
|
|
simple-statement = [assignment-statement |
|
|
procedure-statement |
|
|
goto-statement |
|
|
assertion
|
|
.in -\w'['u
|
|
]
|
|
.in -\w'simple-statement = 'u
|
|
.XE
|
|
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 on, 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.
|
|
If the s-option is turned on, the compiler will not know a thing about
|
|
assertions, so using assertions will then give a parse error.
|
|
.LP
|
|
.ft I
|
|
4. Additional procedures.
|
|
.LP
|
|
Three additional standard procedures are available:
|
|
.IP "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.
|
|
If not, it will be zero.
|
|
.IP release:
|
|
.IP 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!
|
|
.RE
|
|
.LP
|
|
.ft I
|
|
5. UNIX interfacing.
|
|
.LP
|
|
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.
|
|
.LP
|
|
.ft I
|
|
6. Double length (32 bit) integers.
|
|
.LP
|
|
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 \(mi2147483648 .. +2147483647.
|
|
Long constants can not be declared.
|
|
Longs can not be used as control-variables.
|
|
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.
|
|
It is possible to read longs from a file of integers
|
|
and vice-versa, but only if longs and integers have the same size.
|
|
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
|
|
.PP
|
|
.RS
|
|
conversion error, trap 10, non-fatal
|
|
.RE
|
|
.LP
|
|
.ft I
|
|
7. Underscore as letter.
|
|
.LP
|
|
The character '_' may be used in forming identifiers, if the u- or U-option
|
|
is turned on.
|
|
It is forbidden to start identifiers with underscores, since
|
|
this may cause name-clashes with run-time routines.
|
|
.LP
|
|
.ft I
|
|
8. Zero field width in write.
|
|
.LP
|
|
Zero TotalWidth arguments are allowed.
|
|
In this case, no characters are written for
|
|
character, string or Boolean type arguments.
|
|
A zero FracDigits
|
|
argument for fixed-point representation of reals causes the fraction and
|
|
the character '.' to be suppressed.
|
|
.LP
|
|
.ft I
|
|
9. Pre-processing.
|
|
.LP
|
|
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.
|
|
.in 0
|
|
.SS "Deviations from the standard"
|
|
.PP
|
|
.MX
|
|
Pascal deviates from the standard in the following ways:
|
|
.IP 1.
|
|
Standard procedures and functions are not allowed as parameters in
|
|
.MX
|
|
Pascal.
|
|
You can obtain the same result with negligible loss of performance
|
|
by declaring some user routines like:
|
|
.XS
|
|
.CW
|
|
function sine(x:real):real;
|
|
begin
|
|
sine:=sin(x)
|
|
end;
|
|
.ft R
|
|
.XE
|
|
.IP 2.
|
|
The standard procedures read, readln, write and writeln are implemented as
|
|
word-symbols, and can therefore not be redeclared.
|
|
.SS "Compiler options"
|
|
.PP
|
|
Some options of the compiler may be controlled by using '{$....}'.
|
|
Each option consists of a lower case letter followed by +, \(mi or an unsigned
|
|
number.
|
|
Options are separated by commas.
|
|
The following options exist:
|
|
.IP a+/\(mi
|
|
This option switches assertions on and off.
|
|
If this option is on, then code is included to test these assertions
|
|
at run time.
|
|
Default +.
|
|
.IP c+/\(mi
|
|
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 \(mi.
|
|
.IP d+/\(mi
|
|
This option, if on, allows you to use variables of type 'long'.
|
|
Default \(mi.
|
|
.IP i<num>
|
|
.br
|
|
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.
|
|
.IP l+/\(mi
|
|
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.
|
|
Default +.
|
|
.IP r+/\(mi
|
|
If + then code is inserted to check subrange variables against
|
|
lower and upper subrange limits.
|
|
Default +.
|
|
.IP s+/\(mi
|
|
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 \(mi.
|
|
.IP t+/\(mi
|
|
If + then each time a procedure is entered, the routine 'procentry' is
|
|
called, and each time a procedure exits, the procedure 'procexit' is
|
|
called.
|
|
Both 'procentry' and 'procexit' have a 'string' as parameter.
|
|
This means that when a user specifies his or her own procedures, the c-option
|
|
must be used.
|
|
Default procedures are present in the run time library.
|
|
Default \(mi.
|
|
.IP u+/\(mi
|
|
If + then the character '_' is treated like a letter,
|
|
so that it may be used in identifiers.
|
|
Procedure and function identifiers are not allowed to start with an
|
|
underscore because they may collide with library routine names.
|
|
Default \(mi.
|
|
.PP
|
|
Some of these flags (c, d, i, s, u, C and U) are only effective when
|
|
they appear before the 'program' symbol.
|
|
The others may be switched
|
|
on and off.
|
|
.PP
|
|
A very powerful debugging tool is the knowledge that inaccessible statements
|
|
and useless tests are removed by the optimizer.
|
|
For instance, a statement like:
|
|
.XS
|
|
.CW
|
|
if debug then
|
|
writeln('initialization done');
|
|
.ft R
|
|
.XE
|
|
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.
|
|
.SS "Library routines"
|
|
.PP
|
|
The following library of external routines for Pascal programs is available:
|
|
.nf
|
|
.SP
|
|
.CW
|
|
.ta 12n
|
|
const bufsize = ?;
|
|
type br1 = 1..bufsize;
|
|
br2 = 0..bufsize;
|
|
br3 = -1..bufsize;
|
|
ok = -1..0;
|
|
buf = packed array[br1] of char;
|
|
alfa = packed array[1..8] of char;
|
|
string = ^packed array[1..?] of char;
|
|
filetype = file of ?;
|
|
long = ?;
|
|
.SP
|
|
{all routines must be declared extern}
|
|
.SP
|
|
function argc:integer;
|
|
function argv(i:integer):string;
|
|
function environ(i:integer):string;
|
|
procedure argshift;
|
|
.SP
|
|
procedure buff(var f:filetype);
|
|
procedure nobuff(var f:filetype);
|
|
procedure notext(var f:text);
|
|
procedure diag(var f:text);
|
|
procedure pcreat(var f:text; s:string);
|
|
procedure popen(var f:text; s:string);
|
|
procedure pclose(var f:filetype);
|
|
.SP
|
|
procedure trap(err:integer);
|
|
procedure encaps(procedure p; procedure q(n:integer));
|
|
.SP
|
|
function perrno:integer;
|
|
function uread(fd:integer; var b:buf; len:br1):br3;
|
|
function uwrite(fd:integer; var b:buf; len:br1):br3;
|
|
.SP
|
|
function strbuf(var b:buf):string;
|
|
function strtobuf(s:string; var b:buf; len:br1):br2;
|
|
function strlen(s:string):integer;
|
|
function strfetch(s:string; i:integer):char;
|
|
procedure strstore(s:string; i:integer; c:char);
|
|
.SP
|
|
function clock:integer;
|
|
.fi
|
|
.ft R
|
|
.PP
|
|
This library contains some often used external routines for Pascal programs.
|
|
The routines can be divided into several categories:
|
|
.PP
|
|
.ti -2
|
|
Argument control:
|
|
.RS
|
|
.IP argc 10
|
|
Gives the number of arguments provided when the program is called.
|
|
.IP argv
|
|
Selects the specified argument from the argument list and returns a
|
|
pointer to it.
|
|
This pointer is nil if the index is out of bounds (<0 or >=argc).
|
|
.IP environ
|
|
Returns a pointer to the i-th environment string (i>=0).
|
|
Returns nil
|
|
if i is beyond the end of the environment list (UNIX version 7).
|
|
.IP argshift
|
|
Effectively deletes the first argument from the argument list.
|
|
Its function is equivalent to \fIshift\fR in the UNIX shell: argv[2] becomes
|
|
argv[1], argv[3] becomes argv[2], etc.
|
|
It is a useful procedure to skip optional flag arguments.
|
|
Note that the matching of arguments and files
|
|
is done at the time a file is opened by a call to reset or rewrite.
|
|
.PP
|
|
.ti -2
|
|
Additional file handling routines:
|
|
.IP buff
|
|
Turn on buffering of a file.
|
|
Not very useful, because all
|
|
files are buffered except standard output to a terminal and diagnostic output.
|
|
Input files are always buffered.
|
|
.IP nobuff
|
|
Turn off buffering of an output file.
|
|
It causes the current contents of the
|
|
buffer to be flushed.
|
|
.IP notext
|
|
Only useful for input files.
|
|
End of line characters are not replaced by a space and character codes out of
|
|
the ASCII range (0..127) do not cause an error message.
|
|
.IP diag
|
|
Initialize a file for output on the diagnostic output stream (fd=2).
|
|
Output is not buffered.
|
|
.IP pcreat
|
|
The same as rewrite(f), except that you must provide the file name yourself.
|
|
The name must be zero terminated.
|
|
Only text files are allowed.
|
|
.IP popen
|
|
The same as reset(f), except that you must provide the file name yourself.
|
|
The name must be zero terminated.
|
|
Only text files are allowed.
|
|
.IP pclose
|
|
Gives you the opportunity to close files hidden in records or arrays.
|
|
All other files are closed automatically.
|
|
.PP
|
|
.ti -2
|
|
String handling:
|
|
.IP strbuf
|
|
Type conversion from character array to string.
|
|
It is your own responsibility that the string is zero terminated.
|
|
.IP strtobuf
|
|
Copy string into buffer until the string terminating zero byte
|
|
is found or until the buffer if full, whatever comes first.
|
|
The zero byte is also copied.
|
|
The number of copied characters, excluding the zero byte, is returned.
|
|
So if
|
|
the result is equal to the buffer length, then the end of buffer is reached
|
|
before the end of string.
|
|
.IP strlen
|
|
Returns the string length excluding the terminating zero byte.
|
|
.IP strfetch
|
|
Fetches the i-th character from a string.
|
|
There is no check against the string length.
|
|
.IP strstore
|
|
Stores a character in a string.
|
|
There is no check against
|
|
string length, so this is a dangerous procedure.
|
|
.PP
|
|
.ti -2
|
|
Trap handling:
|
|
.PP
|
|
These routines allow you to handle almost all
|
|
the possible error situations yourself.
|
|
You may define your own trap handler, replacing the
|
|
default handler that produces an error message and quits.
|
|
You may also generate traps yourself.
|
|
.IP trap
|
|
Trap generates the trap passed as argument (0..252).
|
|
The trap numbers 128..252 may be used freely.
|
|
The others are reserved.
|
|
.IP encaps
|
|
Encapsulate the execution of \fIp\fR with the trap handler \fIq\fR.
|
|
Encaps replaces the previous trap handler by \fIq\fR, calls \fIp\fR
|
|
and restores
|
|
the previous handler when \fIp\fR returns.
|
|
If, during the execution of \fIp\fR, a trap occurs,
|
|
then \fIq\fR is called with the trap number as parameter.
|
|
For the duration of \fIq\fR the previous trap handler is restored, so that
|
|
you may handle only some of the errors in \fIq\fR.
|
|
All the other errors must
|
|
then be raised again by a call to \fItrap\fR.
|
|
.br
|
|
Encapsulations may be nested: you may encapsulate a procedure while executing
|
|
an encapsulated routine.
|
|
.br
|
|
Jumping out of an encapsulated procedure (non-local goto) is dangerous,
|
|
because the previous trap handler must be restored.
|
|
Therefore, you may only jump out of procedure \fIp\fR from inside \fIq\fR and
|
|
you may only jump out of one level of encapsulation.
|
|
If you want to exit several levels of encapsulation, use traps.
|
|
See pc_prlib(7) for lists of trap numbers
|
|
for EM machine errors and Pascal run time system errors.
|
|
Note that \fIp\fR may not have parameters.
|
|
.PP
|
|
.ti -2
|
|
UNIX system calls:
|
|
.IP uread
|
|
Equal to the read system call.
|
|
Its normal name is blocked by the standard Pascal routine read.
|
|
.IP uwrite
|
|
As above but for write(2).
|
|
.IP perrno
|
|
Because external data references are not possible in Pascal,
|
|
this routine returns the global variable \fIerrno\fR, indicating the result of
|
|
the last system call.
|
|
.PP
|
|
.ti -2
|
|
Miscellaneous:
|
|
.IP clock
|
|
Return the number of ticks of user and system time consumed by the program.
|
|
.PP
|
|
The following program presents an example of how these routines can be used.
|
|
This program is equivalent to the UNIX command cat(1).
|
|
.nf
|
|
.SP
|
|
.CW
|
|
{$c+}
|
|
.CW
|
|
program cat(input,inp,output);
|
|
.CW
|
|
var inp:text;
|
|
.CW
|
|
s:string;
|
|
.SP
|
|
.CW
|
|
function argc:integer; extern;
|
|
.CW
|
|
function argv(i:integer):string; extern;
|
|
.CW
|
|
procedure argshift; extern;
|
|
.CW
|
|
function strlen(s:string):integer; extern;
|
|
.CW
|
|
function strfetch(s:string; i:integer):char; extern;
|
|
.SP
|
|
.CW
|
|
procedure copy(var fi:text);
|
|
.CW
|
|
var c:char;
|
|
.CW
|
|
begin reset(fi);
|
|
.CW
|
|
while not eof(fi) do
|
|
.CW
|
|
begin
|
|
.CW
|
|
while not eoln(fi) do
|
|
.CW
|
|
begin
|
|
.CW
|
|
read(fi,c);
|
|
.CW
|
|
write(c)
|
|
.CW
|
|
end;
|
|
.CW
|
|
readln(fi);
|
|
.CW
|
|
writeln
|
|
.CW
|
|
end
|
|
.CW
|
|
end;
|
|
.SP
|
|
.CW
|
|
begin {main}
|
|
.CW
|
|
if argc = 1 then
|
|
.CW
|
|
copy(input)
|
|
.CW
|
|
else
|
|
.CW
|
|
repeat
|
|
.CW
|
|
s := argv(1);
|
|
.CW
|
|
if (strlen(s) = 1) and (strfetch(s,1) = '-')
|
|
.CW
|
|
then copy(input)
|
|
.CW
|
|
else copy(inp);
|
|
.CW
|
|
argshift;
|
|
.CW
|
|
until argc <= 1;
|
|
.CW
|
|
end.
|
|
.fi
|
|
.ft R
|
|
.PP
|
|
Another example gives some idea of the way to manage trap handling:
|
|
.nf
|
|
.SP
|
|
.CW
|
|
program bigreal(output);
|
|
.CW
|
|
const EFOVFL=4;
|
|
.CW
|
|
var trapped:boolean;
|
|
.CW
|
|
.SP
|
|
.CW
|
|
procedure encaps(procedure p; procedure q(n:integer)); extern;
|
|
.CW
|
|
procedure trap(n:integer); extern;
|
|
.CW
|
|
.SP
|
|
.CW
|
|
procedure traphandler(n:integer);
|
|
.CW
|
|
begin if n=EFOVFL then trapped:=true else trap(n) end;
|
|
.CW
|
|
.SP
|
|
.CW
|
|
procedure work;
|
|
.CW
|
|
var i,j:real;
|
|
.CW
|
|
begin trapped:=false; i:=1;
|
|
.CW
|
|
while not trapped do
|
|
.CW
|
|
begin j:=i; i:=i*2 end;
|
|
.CW
|
|
writeln('bigreal = ',j);
|
|
.CW
|
|
end;
|
|
.CW
|
|
.SP
|
|
.CW
|
|
begin
|
|
.CW
|
|
encaps(work,traphandler);
|
|
.CW
|
|
end.
|
|
.fi
|
|
.ft R
|
|
.PP
|
|
Two routines may cause fatal error messages to be generated.
|
|
These are:
|
|
.IP pcreat
|
|
Rewrite error (trap 77) if the file cannot be created.
|
|
.IP popen
|
|
Reset error (trap 76) if the file cannot be opened for reading
|
|
.SS References
|
|
.IP [1]
|
|
BSI standard BS 6192: 1982 (ISO 7185).
|
|
.IP [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.
|