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Differences to Z.200/1988
*************************
This chapter lists the differences and extensions between GNUCHILL
and the CCITT recommendation Z.200 in its 1988 version (reffered to as
Z.200/1988).
* 2.2 Vocabulary
The definition of <simple name string> is changed to:
<simple name string> ::=
{<letter> | _ } { <letter> | <digit | _ }
* 2.6 Compiler Directives
Only one directive is allowed between the compiler directive
delimiters `<>' and `<>' or the end-of-line, i.e.
<> USE_SEIZE_FILE "foo.grt" <>
<> ALL_STATIC_OFF
* 3.3 Modes and Classes
The syntax of <mode> is changed to:
<mode> ::=
[READ] <non-composite-mode>
| [READ] composite-mode>
<non-composite-mode> ::=
<discrete mode>
| <real modes>
| <powerset modes>
| <reference mode>
| <procedure mode>
| <instance mode>
| <synchronization mode>
| <timing mode>
* 3.4 Discrete Modes
The list of discrete modes is enhanced by the following modes:
BYTE 8-bit signed integer
UBYTE 8-bit unsigned integer
UINT 16-bit unsigned integer
LONG 32-bit signed integer
ULONG 32-bit unsigned integer
*Please note* that INT is implemented as 16-bit signed integer.
* 3.4.6 Range Modes
The mode BIN(n) is not implemented. Using INT(0 : 2 ** n - 1)
instead of BIN(n) makes this mode unneccessary.
* 3.X Real Modes
Note: This is an extension to Z.200/1988, however, it is defined in
Z.200/1992.
syntax:
<real mode> ::=
<floating point mode>
semantics:
A real mode specifies a set of numerical values which approximate a
contiguous range of real numbers.
* 3.X.1 Floating point modes
syntax:
<floating point mode> ::=
<floating point mode name
predefined names:
The names REAL and LONG_REAL are predefined as floating point mode
names.
semantics:
A floating point mode defines a set of numeric approximations to a
range of real values, together with their minimum relative
accuracy, between implementation defined bounds, over which the
usual ordering and arithmetic operations are defined. This set
contains only the values which can be represented by the
implementation.
examples:
REAL
LONG_REAL
* 3.6 Reference Modes
Row modes are not implemeted at all.
* 3.7 Procedure Mode
The syntax for procedure modes is changed to:
<procedure mode> ::=
PROC ([<parameter list>]) [ <result spec> ]
[EXCEPTIONS(<exception list>)] [RECURSIVE]
| <procedure mode name>
<parameter list> ::=
<parameter spec> {, <parameter spec> } *
<parameter spec> ::=
<mode> [ <parameter attribute> ]
<parameter attribute> ::=
IN | OUT | INOUT | LOC
<result spec> ::=
RETURNS ( <mode> [LOC])
<exception list> ::=
<exception name> {, <exception name> } *
* 3.10 Input-Output Modes
Due to the absence of row modes, DYNAMIC has no meaning in an
access or text mode definition.
* 3.12.2 String Modes
As <string modes> were defined differently in Z.200/1984, the
syntax of <string mode> is changed to:
<string mode> ::=
<string type> ( <string length> ) [ VARYING ]
| <parametrized string mode>
| <string mode name>
<parameterized string mode> ::=
<origin string mode name> ( <string length> )
| <parameterized string mode name>
<origin string mode name> ::=
<string mode name>
string type
BOOLS
| BIT
| CHARS
| CHAR
<string length> ::=
<integer literal expression>
VARYING is not implemented for <string type> BIT and BOOL.
* 3.11.1 Duration Modes
The predefined mode DURATION is implemented as a NEWMODE ULONG and
holds the duration value in miliseconds. This gives a maximum
duration of
MILLISECS (UPPER (ULONG)),
SECS (4294967),
MINUTES (71582),
HOURS (1193), and
DAYS (49).
* 3.11.2 Absolute Time Modes
The predefined mode TIME is implemented as a NEWMODE ULONG and
holds the absolute time in seconds since Jan. 1st, 1970. This is
equivalent to the mode `time_t' defined on different systems.
* 3.12.4 Structure Modes
Variant fields are allowed, but the CASE-construct may define only
one tag field (one dimensional CASE). OF course, several variant
fields may be specified in one STRUCT mode. The tag field will
(both at compile- and runtime) not be interpreted in any way,
however, it must be interpreted by a debugger. As a consequence,
there are no parameterized STRUCT modes.
* 3.12.5 Layout description for array and structure modes
STEP and POS is not implemeted at all, therefore the syntax of
<element layout and field layout is changed to:
<element layout> ::=
PACK | NOPACK
<field layout> ::=
PACK | NOPACK
* 3.13.4 Dynamic parameterised structure modes
Dynamic parameterised structure modes are not implemented.
* 4.1.2 Location declaration
The keyword STATIC is allowed, but has no effect at module level,
because all locations declared there are assumed to be `static' by
default. Each granted location will become `public'. A `static'
declaration inside a block, procedure, etc. places the variable in
the data section instead of the stack section.
* 4.1.4 Based decleration
The based declaration was taken from Z.200/1984 and has the
following syntax:
syntax:
<based declaration> ::=
<defining occerrence list> <mode> BASED
( <free reference location name> )
semantics:
A based declaration with <free reference location name> specifies
as many access names as are defining occerrences in the defining
occurrence list. Names declared in a base declaration serve as an
alternative way accessing a location by dereferencing a reference
value. This reference value is contained in the location specified
by the free reference location name. This dereferencing operation
is made each time and only when an access is made via a declared
based name.
static properties:
A defining occurrence in a based declaration with free reference
location name defines a based name. The mode attached to a based
name is the mode specified in the based declaration. A based name
is referable.
* 4.2.2 Access names
The syntax of access names is changed to:
<access name> ::=
<location name>
| <loc-identity name>
| <based name>
| <location enumeration name>
| <location do-with name>
The semantics, static properties and dynamic conditions remain
unchanged except that they are enhanced by base name.
* 5.2.4.1 Literals General
The syntax of <literal> is change to:
<literal> ::=
<integer literal>
| <boolean literal>
| <charater literal>
| <set literal>
| <emptiness literal>
| <character string literal>
| <bit string literal>
| <floating point literal>
Note: The <floating point literal> is an extension to Z.200/1988
and will be described later on.
* 5.2.4.2 Integer literals
The <decimal integer literal> is changed to:
<decimal integer literal> ::=
{ D | d } ' { <digit> | _ } +
| <digit> { <digit> | _ } *
* 5.2.4.4 Character literals
A character literal, e.g. 'M', may serve as a charater string
literal of length 1.
* 5.2.4.7 Character string literals
The syntax of a character string literal is:
<character string literal> ::=
'{ <non-reserved character> | <single quote> |
<control sequence> } * '
| '{ <non-reserved character> | <double quote> |
<control sequence> } * '
<single quote> ::=
"
<double quote> ::=
""
A character string litaral of length 1, enclosed in apostrophes
(e.g. 'M') may also serve as a charater literal.
* 5.2.4.9 Floating point literal
Note: This is an extension to Z.200/1988 ans was taken from
Z.200/1992.
syntax:
<floating point literal> ::=
<unsigned floating point literal>
| <signed floating point literal>
<unsigned floating point literal> ::=
<digit sequence> . [ <digit sequence> ] [ <exponent> ]
| [ <digit sequence> ] . <digit sequence> [ <exponent> ]
<signed floating point literal> ::=
- <unsigned floating point literal>
<digit sequence> ::=
<digit> { <digit> | _ } *
<exponent> ::=
[ E | D | e | d ] <digit sequence>
| [ E | D | e | d ] - <digit sequence>
* 5.2.14 Start Expression
The START expression is not implemented.
* 5.3 Values and Expressions
The undefined value, denoted by `*', is not implemented.
* 5.3.8 Operand-5
The <string repetition operator> is defined as:
<string repetition operator> ::=
(<integer expression>)
* 6.4 Case Action
There may be only one case selector specified. The optional range
list must not be specified.
* 6.5 Do Action
A Do-Action without control part is not implemented. Grouping of
statements can be achieved via BEGIN and END. A location
enumeration is not allowed for BIT strings, only for (varying)
CHAR strings and ARRAYs.
The expression list in a DO WITH must consist of locations only.
* 6.13 Start Action
The syntax of the START action is changed to:
<start action> ::=
START <process name> (<copy number> [, <actual parameter list>])
[ SET <instance location> ]
<copy number> ::=
<integer expression>
* 6.16 Delay Action
The optional PRIORITY specification need not be a constant.
* 6.17 Delay Case Action
The optional SET branch and the, also optional, PRIORITY branch
must be seperated by `;'.
* 6.18 Send Action
The send action must define a destination instance (via the TO
branch), since undirected signals are not supported. The optional
PRIORITY specification need not be a constant. Additional to the
data transported by the signal, there will be a user defined
argument.
The syntax of the <send signal action> is therefore:
<send signal action> ::=
SEND <signal name> [ ( <value> {, <value> } * ) ]
[ WITH <expression> ]
TO <instance primitive value> [ <priority> ]
The default priority can be specified by the compiler directive
SEND_SIGNAL_DEFAULT_PRIORITY. If this also is omitted, the default
priority is 0.
* 6.20.3 CHILL value built-in calls
The CHILL value buit-in calls are enhanced by some calls, and
other calls will have different arguments as described in
Z.200/1988. Any call not mentioned here is the same as described
in Z.200/1988.
syntax:
CHILL value built-in routine call> ::=
ADDR (<location>)
| PRED (<pred succ argument>)
| SUCC (<pred succ argument>)
| ABS (<numeric expression>)
| LENGTH (<length argument>)
| SIN (<floating point expression>)
| COS (<floating point expression>)
| TAN (<floating point expression>)
| ARCSIN (<floating point expression>)
| ARCCOS (<floating point expression>)
| ARCTAN (<floating point expression>)
| EXP (<floating point expression>)
| LN (<floating point expression>)
| LOG (<floating point expression>)
| SQRT (<floating point expression>)
| QUEUE_LENGTH (<buffer location> | <event location>)
| GEN_INST (<integer expression> | <process name> ,
<integer expression>)
| COPY_NUMBER (<instance expression>)
| GEN_PTYE (<process name>)
| PROC_TYPE (<instance expression>)
| GEN_CODE (<process name> | <signal name>)
| DESCR (<location>)
<pred succ argument> ::=
<discrete expression>
| <bound reference expression>
<numeric expression> ::=
<integer expression>
| floating point expression>
<length argument> ::=
<string location>
| <string expression>
| <string mode name>
| <event location>
| <event mode name>
| <buffer location>
| <buffer mode name>
| <text location>
| <text mode name>
semantics:
ADDR is derived syntax for -> <location>.
PRED and SUCC delivers respectively, in case of a discrete
expression, the next lower or higher discrete value of their
argument, in case of bound reference expression these built-in
calls deliver a pointer to the previous or next element.
ABS is defined on numeric values, i.e. integer values and floating
point values, delivering the corresponding absolute value.
LENGTH is defined on
* string and text locations and string expressions, delivering
the length of them;
* event locations, delivering the event length of the mode of
the location;
* buffer locations, delivering the buffer length of the mode of
the location;
* string mode names, delivering the string length of the mode;
* text mode names, delivering the text length of the mode;
* buffer mode names, delivering the buffer length of the mode;
* event mode names, delivering the event length of the mode;
* Additionally, LENGTH also may be used on the left hand side
of an assignment to set a new length of a varying character
string location. However, to avoid undefined elements in the
varying string, the new length may only be less or equal to
the current length. Otherwise a RANGEFAIL exception will be
generated.
SIN delivers the sine of its argument (interpreted in radians).
COS delivers the cosine of its argument (interpreted in radians).
TAN delivers the tangent of its argument (interpreted in radians).
ARCSIN delivers the sin -1 function of its argument.
ARCCOS delivers the cos -1 function of its argument.
ARCTAN delivers the tan -1 function of its argument.
EXP delivers the exponential function, where x is the argument.
LN delivers the natural logarithm of its argument.
LOG delivers the base 10 logarithm of its argument.
SQRT delivers the sqare root of its argument.
QUEUE_LENGTH delivers either the number of sending delayed
processes plus the number of messages in a buffer queue (if the
argument is a buffer location), or the number of delayed processes
(if the argument specifies an event location) as integer
expression.
GEN_INST delivers an instance expression constructed from the
arguments. Both arguments must have the &INT-derived class.
COPY_NUMBER delivers as &INT-derived class the copy number of an
instance location.
GEN_PTYPE delivers as &INT-derived class the associated number of
the process name.
PROC_TYPE delivers as &INT-derived class the process type of an
instance expression.
GEN_CODE delivers as &INT-derived class the associated number of
the process name or signal name.
DESCR delivers a free reference expression pointing to a structure
with the following layout describing the location argument.
SYNMODE __tmp_descr = STRUCT (p PTR, l ULONG);
* 7.4.2 Associating an outside world object
The syntax of the associate built-in routine call is defined as:
<associate built-in routine call> ::=
ASSOCIATE ( <association location>, <string expression>, [, <string expression> ] )
The ASSOCIATE call has two parameters besides the association
location: a pathname and an optional mode string.
The value of the first string expression must be a pathname
according to the rules of the underlying operating system. (Note
that a relative pathname implies a name relative to the working
directory of the process.)
The mode string may contain the value "VARIABLE", which requests
an external representation of records consisting of an UINT record
length followed by as many bytes of data as indicated by the
length field. Such a file with variable records is not indexable.
A file with variable records can be written using any record mode.
If the record mode is CHARS(n) VARYING, the record length is equal
to the actual length of the value written. (Different record may
have differing lengths.) With all other record modes, all records
written using the same access mode will have the same length, but
will still be prefixed with the length field. (Note that by
re-connecting with different access modes, the external
representation may ultimately contain records with differing
lengths.)
A file with variable records can only be read by using a record
mode of CHARS(n) VARYING.
* 7.4.2 Accessing association attributes
The value of the READABLE and WRITEABLE attributes is determined
using the file status call provided by the operating system. The
result will depend on the device being accessed, or on the file
mode.
The INDEXABLE attribute has the value false for files with
variable records, and for files associated with devices not
supporting random positioning (character devices, FIFO special
files, etc.).
The variable attribute is true for files associated with the mode
sting "VARIABLE", and false otherwise.
* 7.4.5 Modifying association attributes
The syntax of the MODIFY built-in routine call is defined as:
<modify built-in call> ::=
MODIFY ( <association location>, <string expression> )
At present, MODIFY accepts a character string containing a pathname
in addition to the association location, which will cause a
renaming of the associated file.
* 7.4.9 Data transfer operations
READRECORD will fail (causing READFAIL) if the number of bytes
from the current position in the file to the end of the file is
greater than zero but less than the size of the record mode, and
no data will be transferred. (If the number of bytes is zero, no
error occurs and OUTOFFILE will return TRUE.)
The number of bytes transferred by READRECORD and WRITERECORD is
equal to the size of the record mode of the access location. Note
that the internal representation of this mode may vary depending
on the record mode being packed or not.
* 7.5 Text Input Output
Sequential text files will be represented so as to be compatible
with the standard representation of texts on the underlying
operating system, where control characters are used to delimit
text records on files as well as to control the movement of a
cursor or printing head on a device.
For indexed text files, records of a uniform length (i.e. the size
of the text record, including the length field) are written. All
i/o codes cause an i/o transfer without any carriage control
characters being added to the record, which will be expanded with
spaces.
An indexed text file is therefore not compatible with the standard
text representation of the underlying operating system.
* 7.5.3 Text transfer operations
The syntax of <text argument> is changed to:
<text argument> ::=
<text location>
| <predefined text location>
| <varying string location>
<predefined text location> ::=
STDIN
| STDOUT
| STDERR
NOTE: The identifiers STDIN, STDOUT, and STDERR are predefined.
Association and connection with files or devices is done according
to operating system rules.
The effect of using READTEXT or WRITETEXT with a character string
location as a text argument (i.e. the first parameter) where the
same location also appears in the i/o list is undefined.
The current implementation of formatting assumes run-to-completion
semantics of CHILL tasks within an image.
* 7.5.5 Conversion
Due to the implementation of <floating point modes> the syntax is
changed to:
<conversion clause> ::=
<conversion code> { <conversion qualifier } *
[ <clause width> ]
<conversion code> ::=
B | O | H | C | F
<conversion qualifier> ::=
L | E | P<character>
<clause width> ::=
{ <digit> } + | V
| <real clause width>
<real clause width> ::=
{ { <digit> + | V } : { { <digit> } + | V }
Note: The <real clause width> is only valid for <conversion code>
`C' or `F'.
* 7.5.7 I/O control
To achieve compatibility of text files written with CHILL i/o with
the standard representation of text on the underlying operating
system the interpretation of the i/o control clause of the format
deviates from Z.200. The following table shows the i/o codes
together with the control characters written before and after the
text record, to achieve the indicated function:
`/'
Write next record (record, line feed)
`+'
Write record on next page (form feed, record, line feed)
`-'
Write record on current line (record, carriage return)
`?'
Write record as a prompt (carriage return, record)
`!'
Emit record (record).
`='
Force new page for the next line: The control character
written before the next record will be form feed,
irrespective of the i/o control used for transferring the
record.
When reading a text file containing control characters other than
line feed, these characters have to be reckoned with by the format
used to read the text records.
* 11.2.2 Regionality
Regionality is not implemented at all, so there is no difference
in the generated code when REGION is substituted by MODULE in a
GNUCHILL compilation unit.
* 11.5 Signal definition statement
The <signal definition statement> may only occur at module level.
* 12.3 Case Selection
The syntax of <case label specification> is changed to:
<case label specification> ::=
( <case label> {, <case label> } * )
<case label> ::=
<discrete literal expression>
| <literal range>
| <discrete mode name>
| ELSE
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