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@\input texinfo @c -*-texinfo-*-
@setfilename chill.info
@settitle Guide to GNU Chill


@ifinfo
@format
START-INFO-DIR-ENTRY
* Chill: (chill).               Chill compiler
END-INFO-DIR-ENTRY
@end format
@end ifinfo

@titlepage
@title GNU Chill
@author William Cox, Per Bothner, Wilfried Moser
@end titlepage
@contents

@ifinfo
@node Top
@top

@menu
* Options::               Compiler options
* Missing::               Unimplemented parts of the Chill language
* Enhancements::          GNU-specific enhancements to the Chill language
* Conversions::           Value and location conversions
* Separate compilation::  Separate compilation
* Differences::           Differences between GNUCHILL and Z.200/1988
* Directives::            Implemented Compiler Directives
* References::            Language definition references
@end menu

@end ifinfo

@node Options
@chapter Compiler options

Invoking the compiler:

The @sc{gnu} CHILL compiler supports several new command line options, and
brings a new use to another:

@table @code
@item -lang-chill
This option instructs gcc that the following file is a CHILL source file,
even though its extension is not the default `.ch'.

@item -flocal-loop-counter
The CHILL compiler makes a separate reach, or scope,
for each DO FOR loop.  If @code{-flocal-loop-counter} is
specified, the loop counter of value enumeration and location
enumeration is automatically declared inside that reach.
This is the default behavior, required by Z.200.

@item -fno-local-loop-counter
When this option is specified, the above automatic declaration
is not performed, and the user must declare all loop counters 
explicitly.

@item -fignore-case
When this option is specified, the compiler ignores case. All 
identifiers are converted to lower case. This enables the usage
of C runtime libraries.

@item -fno-ignore-case
Ignoring the case of identifiers is turned off.

@item -fruntime-checking
The CHILL compiler normally generates code to check 
the validity of expressions assigned to variables or
expressions passed as parameters to procedures and processes,
if those expressions cannot be checked at compile time.
This is the default behavior, required by Z.200.
This option allows you to re-enable the default behavior
after disabling it with the @code{-fno-runtime-checking}
option.

@item -fno-runtime-checking
The CHILL compiler normally generates code to check 
the validity of expressions assigned to variables, or
expressions passed as parameters to procedures and processes.
This option allows you to disable that code generation.
This might be done to reduce the size of a program's
generated code, or to increase its speed of execution.
Compile time range-checking is still performed.

@item -fgrant-only
@itemx -fchill-grant-only
This option causes the compiler to stop successfully
after creating the grant file specified by the source
file (see modular programming in CHILL).  No code is
generated, and many categories of errors are not reported.

@item -fold-string
Implement the semantics of Chill 1984 with respect to strings:
String indexing yields a slice of length one;  CHAR is similar
to CHAR(1) (or CHARS(1)); and BOOL is similar to BIT(1) (or BOOLS(1)).

@item -fno-old-string
Don't implement 1984 Chill string semantics.  This is the default.

@item -I@var{seize_path}
This directive adds the specified seize path to the compiler's
list of paths to search for seize files.  When processing a 
USE_SEIZE_FILE directive, the compiler normally searches for
the specified seize file only in the current directory.  When
one or more seize paths are specified, the compiler also 
searches in those directories, in the order of their
specification on the command line, for the seize file.

@item -c
This C-related switch, which normally prevents gcc from 
attempting to link, is *not* yet implemented by the @code{chill} command,
but you can use the @code{gcc} command with this flag.
@end table

@node Missing
@chapter Implemented and missing parts of the Chill language

The numbers in parentheses are Z.200(1988) section numbers.

@itemize @bullet
@item The FORBID keyword in a GRANT statement is currently ignored.

@item A CASE action or expression allows only a single expression
in a case selector list (5.3.2, 6.4).

@item ROW modes are not implemented (3.6.3, 3.13.4).

@item Due to the absence of ROW modes, DYNAMIC has no meaning in
connection with access and text modes.

@item Array and structure layout (PACK, POS, NOPACK, 
STEP keywords) is ignored (3.12.6).

@item Bit-string slices are not implemented.

@item The support for synchronization modes and concurrent execution
is slightly non-standard.

@item Exception handling is implemented, but exceptions are not
generated in all of the required situations.

@item Dynamic modes are not implemented (though string slices should work).

@item Reach-bound initializations are not implemented (4.1.2).

@end itemize

@node Enhancements
@chapter GNU-specific enhancements to the Chill language

@itemize @bullet
@item Grantfiles.  See @xref{Separate compilation}.
@item Precisions.  Multiple integer and real precisions are supported,
as well as signed and unsigned variants of the integer modes.
@item DESCR built-in. The new built-in function 
DESCR ( <descriptor argument> ) returns a pointer to 
STRUCT( addr PTR, length ULONG ) where <descriptor argument> can be
anything the compiler can handle but at least a location of any mode
(except synchronizing modes) and any character string or powerset value.
(A temporary location within the current stack frame may be allocated
if an expression is used.)

CHILL does not permit the writing of procedures with parameters of
any type. Yet some interfaces---in particular those to system 
calls---require
the handling of a wide range of modes, e.g. any string mode, any structure
mode, or any powerset mode. This could be handled by specifying two
parameters (PTR, INT for the length) but this is error-prone (no guarantee
the same location is used after in ADDR and LENGTH), and it will not be
possible for expressions.

Caveats: This feature permits the programmer to obtain the address of
a literal (if the compiler takes this shortcut---see 1st example below).
If hardware features protect constant parts of the program, erronous
abuse will be detected.

    Examples:
       OFFER_HANDLER( descr("dbs"), ->dbs);

       SYNMODE m_els = SET( ela, elb, elc );
       SYNMODE m_elsel = POWERSET m_els;
       DCL user_buf STRUCT( a mx, b my, c mz);
       DCL select POWERSET m_elsel;

       select := m_elsel[LOWER(m_els) : UPPER(m_els)];

       GET_RECORD( relation, recno, descr(user_buf), descr(select) );

       PUT_RECORD( relation, recno, descr(user_buf.b), descr(m_elsel[elb]) );

@item LENGTH built-in on left-hand-side.       The LENGTH built-in may be
used on the left-hand-side of an assignment, where its argument is a VARYING
character string.
@end itemize

@node Conversions
@chapter Value and location conversions

Value and location conversions are highly dependent on the target machine.
They are also very loosely specified in the 1988 standard.
(The 1992 standard seems an improvement.)

The GNU Chill compiler interprets @code{@var{mode}(@var{exp})} as follows:

@itemize @bullet
@item
If @var{exp} is a referable location,
and the size of (the mode of) @var{exp} is the same as the size of @var{mode},
a location conversion is used.
It is implemented exactly as:  @code{(@var{refmode}(-> @var{exp}))->},
where @var{refmode} is a synmode for @code{REF @var{mode}}.

The programmer is responsible for making sure that alignment
restrictions on machine addresses are not violated.

If both @var{mode} and the mode of @var{exp} are discrete modes,
alignment should not be a problem, and we get the same conversion
as a standard value conversion.

@item
If @var{exp} is a constant,
and the size of (the mode of) @var{exp} is the same as the size of @var{mode},
then a value conversion is performed.  This conversion is done
at compile time, and it has not been implemented for all types.
Specifically, converting to or from a floating-point type is not implemented.

@item
If both @var{mode} and the mode of @var{exp} are discrete modes,
then a value conversion is performed, as described in Z.200.

@item
If both @var{mode} and the mode of @var{exp} are reference modes,
then a value conversion is allowed.
The same is true is one mode is a reference mode, and the other
is an integral mode of the same size.

@end itemize

@node Separate compilation
@chapter Separate compilation

The GNU CHILL compiler supports modular programming.  It
allows the user to control the visibility of variables
and modes, outside of a MODULE, by the use of GRANT
and SEIZE directives.  Any location or mode may be made
visible to another MODULE by GRANTing it in the MODULE
where it is defined, and SEIZEing it in another MODULE
which needs to refer to it.

When variables are GRANTed in one or more modules of a
CHILL source file, the compiler outputs a grant file,
with the original source file name as the base name,
and the extension `.grt'.  All of the variables and modes
defined in the source file are written to the grant file,
together with any use_seize_file directives, and the
GRANT directives.  A grant file is created for every such
source file, except if an identical grant file already 
exists.  This prevents unnecessary makefile activity.

The referencing source file must:

@enumerate
@item specify the grant file in a use_seize_file directive, and
@item SEIZE each variable or mode definition that it needs.
@end enumerate

An attempt to SEIZE a variable or mode which is not
GRANTed in some seize file is an error.

An attempt to refer to a variable which is defined in
some seize file, but not explicitly granted, is an
error.

An attempt to GRANT a variable or mode which is not
defined in the current MODULE is an error.

Note that the GNU CHILL compiler will *not* write out a
grant file if:

@itemize @bullet
@item there are no GRANT directives in the source file, or
@item the entire grant file already exists, and is
     identical to the file which the compiler has just built.
(This latter ``feature'' may be removed at some point.)
@end itemize

Otherwise, a grant file is an automatic, unsuppressable
result of a successful CHILL compilation.

A future release will also support using remote spec modules
in a similar (but more Blue Book-conforming) manner.

@node Differences
@chapter 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).

@itemize @bullet

@item 2.2 Vocabulary@*
The definition of @i{<simple name string>} is changed to:

@example
@i{<simple name string> ::=}
@example
@i{@{<letter> | _ @} @{ <letter> | <digit | _ @}}
@end example
@end example

@item 2.6 Compiler Directives@*
Only one directive is allowed between the compiler directive delimiters
`<>' and `<>' or the end-of-line, i.e.
@example
<> USE_SEIZE_FILE "foo.grt" <>
<> ALL_STATIC_OFF
@end example

@item 3.3 Modes and Classes@*
The syntax of @i{<mode>} is changed to:

@example
@i{<mode> ::=}
@example
  [@b{READ}] @i{<non-composite-mode>}
| [@b{READ}] @i{composite-mode>}
@end example

@i{<non-composite-mode> ::=}
@example
  @i{<discrete mode>}
| @i{<real modes>}
| @i{<powerset modes>}
| @i{<reference mode>}
| @i{<procedure mode>}
| @i{<instance mode>}
| @i{<synchronization mode>}
| @i{<timing mode>}
@end example
@end example

@item 3.4 Discrete Modes@*
The list of discrete modes is enhanced by the following modes:

@example
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
@end example

@strong{Please note} that INT is implemented as 16-bit signed integer.

@item 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.

@item 3.X Real Modes@*
Note: This is an extension to Z.200/1988, however, it is defined in
Z.200/1992.

@b{syntax:}

@example
@i{<real mode> ::=}
@example
@i{<floating point mode>}
@end example
@end example

@b{semantics:}

@example
A real mode specifies a set of numerical values which approximate a
contiguous range of real numbers.
@end example

@item 3.X.1 Floating point modes@*

@b{syntax:}

@example
@i{<floating point mode> ::=}
@example
@i{<floating point mode name}
@end example
@end example

@b{predefined names:}

The names @i{REAL} and @i{LONG_REAL} are predefined as @b{floating
point mode} names.

@b{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.

@b{examples:}

@example
@i{REAL}
@i{LONG_REAL}
@end example

@item 3.6 Reference Modes@*
Row modes are not implemeted at all.

@item 3.7 Procedure Mode@*
The syntax for procedure modes is changed to:

@example
@i{<procedure mode> ::=}
@example
  @b{PROC} @i{([<parameter list>]) [ <result spec> ]}
  @i{[}@b{EXCEPTIONS}@i{(<exception list>)] [}@b{RECURSIVE}@i{]}
| @i{<procedure mode name>}
@end example

@i{<parameter list> ::=}
@example
@i{<parameter spec> @{, <parameter spec> @} *}
@end example

@i{<parameter spec> ::=}
@example
@i{<mode> [ <parameter attribute> ]}
@end example

@i{<parameter attribute> ::=}
@example
@b{IN} | @b{OUT} | @b{INOUT} | @b{LOC}
@end example

@i{<result spec> ::=}
@example
@b{RETURNS} @i{( <mode> [}@b{LOC}@i{])}
@end example

@i{<exception list> ::=}
@example
@i{<exception name> @{, <exception name> @} *}
@end example
@end example


@item 3.10 Input-Output Modes@*
Due to the absence of row modes, DYNAMIC has no meaning in an access
or text mode definition.


@item 3.12.2 String Modes@*
As @i{<string modes>} were defined differently in Z.200/1984, the syntax
of @i{<string mode>} is changed to:

@example
@i{<string mode> ::=}
@example
  @i{<string type> ( <string length> ) [} @b{VARYING} @i{]}
| @i{<parametrized string mode>}
| @i{<string mode name>}
@end example

@i{<parameterized string mode> ::=}
@example
  @i{<origin string mode name> ( <string length> )}
| @i{<parameterized string mode name>}
@end example

@i{<origin string mode name> ::=}
@example
@i{<string mode name>}
@end example

@i{string type}
@example
  @b{BOOLS}
| @b{BIT}
| @b{CHARS}
| @b{CHAR}
@end example

@i{<string length> ::=}
@example
@i{<integer literal expression>}
@end example
@end example

@b{VARYING} is not implemented for @i{<string type>} @b{BIT}
and @b{BOOL}.

@item 3.11.1 Duration Modes@*
The predefined mode @i{DURATION} is implemented as a NEWMODE ULONG and
holds the duration value in miliseconds. This gives a maximum duration
of

@example
MILLISECS (UPPER (ULONG)),
SECS (4294967),
MINUTES (71582),
HOURS (1193), and
DAYS (49).
@end example

@item 3.11.2 Absolute Time Modes@*
The predefined mode @i{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.

@item 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.

@item 3.12.5 Layout description for array and structure modes@*
STEP and POS is not implemeted at all, therefore the syntax of
@i{<element layout} and @i{field layout} is changed to:

@example
@i{<element layout> ::=}
@example
@b{PACK} | @b{NOPACK}
@end example

@i{<field layout> ::=}
@example
@b{PACK} | @b{NOPACK}
@end example
@end example

@item 3.13.4 Dynamic parameterised structure modes@*
Dynamic parameterised structure modes are not implemented.

@item 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.

@item 4.1.4 Based decleration@*
The based declaration was taken from Z.200/1984 and has the following
syntax:

@b{syntax:}

@example
@i{<based declaration> ::=}
@example
@i{<defining occerrence list> <mode>} @b{BASED}
@i{( <free reference location name> )}
@end example
@end example

@b{semantics:}

A based declaration with @i{<free reference location name>} specifies
as many access names as are defining occerrences in the @i{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 @i{free reference location name}. This dereferencing operation is 
made each time and only when an access is made via a declared @b{based} 
name.

@b{static properties:}

A defining occurrence in a @i{based declaration} with @i{free reference
location name} defines a @b{based} name. The mode attached to a
@b{based} name is the @i{mode} specified in the @i{based declaration}. A
@b{based} name is @b{referable}.

@item 4.2.2 Access names@*
The syntax of access names is changed to:

@example
@i{<access name> ::=}
@example
  @i{<location name>}
| @i{<loc-identity name>}
| @i{<based name>}
| @i{<location enumeration name>}
| @i{<location do-with name>}
@end example
@end example

The semantics, static properties and dynamic conditions remain
unchanged except that they are enhanced by @i{base name}.

@item 5.2.4.1 Literals General@*
The syntax of @i{<literal>} is change to:

@example
@i{<literal> ::=}
@example
  @i{<integer literal>}
| @i{<boolean literal>}
| @i{<charater literal>}
| @i{<set literal>}
| @i{<emptiness literal>}
| @i{<character string literal>}
| @i{<bit string literal>}
| @i{<floating point literal>}
@end example
@end example

Note: The @i{<floating point literal>} is an extension to Z.200/1988 and
will be described later on.

@item 5.2.4.2 Integer literals@*
The @i{<decimal integer literal>} is changed to:

@example
@i{<decimal integer literal> ::=}
@example
  @i{@{ D | d @} ' @{ <digit> | _ @} +}
| @i{<digit> @{ <digit> | _ @} *}
@end example
@end example

@item 5.2.4.4 Character literals@*
A character literal, e.g. 'M', may serve as a charater string literal of
length 1.

@item 5.2.4.7 Character string literals@*
The syntax of a character string literal is:

@example
@i{<character string literal> ::=}
@example
  @i{'@{ <non-reserved character> | <single quote> |}
  @i{<control sequence> @} * '}
| @i{'@{ <non-reserved character> | <double quote> |}
  @i{<control sequence> @} * '}
@end example

@i{<single quote> ::=}
@example
@i{''}
@end example

@i{<double quote> ::=}
@example
@i{""}
@end example
@end example

A character string litaral of length 1, enclosed in apostrophes
(e.g. 'M') may also serve as a charater literal.

@item 5.2.4.9 Floating point literal@*
Note: This is an extension to Z.200/1988 ans was taken from Z.200/1992.

@b{syntax:}

@example
@i{<floating point literal> ::=}
@example
  @i{<unsigned floating point literal>}
| @i{<signed floating point literal>}
@end example

@i{<unsigned floating point literal> ::=}
@example
  @i{<digit sequence> . [ <digit sequence> ] [ <exponent> ]}
| @i{[ <digit sequence> ] . <digit sequence> [ <exponent> ]}
@end example

@i{<signed floating point literal> ::=}
@example
@i{- <unsigned floating point literal>}
@end example

@i{<digit sequence> ::=}
@example
@i{<digit> @{ <digit> | _ @} *}
@end example

@i{<exponent> ::=}
@example
  @i{[ E | D | e | d ] <digit sequence>}
| @i{[ E | D | e | d ] - <digit sequence>}
@end example
@end example

@item 5.2.14 Start Expression@*
The START expression is not implemented.

@item 5.3 Values and Expressions@*
The undefined value, denoted by `*', is not implemented.

@item 5.3.8 Operand-5@*
The @i{<string repetition operator>} is defined as:

@example
@i{<string repetition operator> ::=}
@example
@i{(<integer expression>)}
@end example
@end example

@item 6.4 Case Action@*
There may be only one case selector specified. The optional range list
must not be specified.

@item 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.

@item 6.13 Start Action@*
The syntax of the START action is changed to:

@example
@i{<start action> ::=}
@example
@b{START} @i{<process name> (<copy number> [, <actual parameter list>])}
@i{[} @b{SET} @i{<instance location> ]}
@end example

@i{<copy number> ::=}
@example
@i{<integer expression>}
@end example
@end example

@item 6.16 Delay Action@*
The optional PRIORITY specification need not be a constant.

@item 6.17 Delay Case Action@*
The optional SET branch and the, also optional, PRIORITY branch must be
separated by `;'.

@item 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 @i{<send signal action>} is therefore:

@example
@i{<send signal action> ::=}
@example
@b{SEND} @i{<signal name> [ ( <value> @{, <value> @} * ) ]}
@i{[} @b{WITH} @i{<expression> ]}
@b{TO} @i{<instance primitive value> [ <priority> ]}
@end example
@end example

The default priority can be specified by the compiler directive
SEND_SIGNAL_DEFAULT_PRIORITY. If this also is omitted, the default
priority is 0.

@item 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.

@b{syntax:}

@example
@i{CHILL value built-in routine call> ::=}
@example
  @i{ADDR (<location>)}
| @i{PRED (<pred succ argument>)}
| @i{SUCC (<pred succ argument>)}
| @i{ABS (<numeric expression>)}
| @i{LENGTH (<length argument>)}
| @i{SIN (<floating point expression>)}
| @i{COS (<floating point expression>)}
| @i{TAN (<floating point expression>)}
| @i{ARCSIN (<floating point expression>)}
| @i{ARCCOS (<floating point expression>)}
| @i{ARCTAN (<floating point expression>)}
| @i{EXP (<floating point expression>)}
| @i{LN (<floating point expression>)}
| @i{LOG (<floating point expression>)}
| @i{SQRT (<floating point expression>)}
| @i{QUEUE_LENGTH (<buffer location> | <event location>)}
| @i{GEN_INST (<integer expression> | <process name> ,}
               @i{<integer expression>)}
| @i{COPY_NUMBER (<instance expression>)}
| @i{GEN_PTYE (<process name>)}
| @i{PROC_TYPE (<instance expression>)}
| @i{GEN_CODE (<process name> | <signal name>)}
| @i{DESCR (<location>)}
@end example

@i{<pred succ argument> ::=}
@example
  @i{<discrete expression>}
| @i{<bound reference expression>}
@end example

@i{<numeric expression> ::=}
@example
  @i{<integer expression>}
| @i{floating point expression>}
@end example

@i{<length argument> ::=}
@example
  @i{<string location>}
| @i{<string expression>}
| @i{<string mode name>}
| @i{<event location>}
| @i{<event mode name>}
| @i{<buffer location>}
| @i{<buffer mode name>}
| @i{<text location>}
| @i{<text mode name>}
@end example
@end example

@b{semantics:}

@i{ADDR} is derived syntax for -> @i{<location>}.

@i{PRED} and @i{SUCC} delivers respectively, in case of a @i{discrete
expression}, the next lower or higher discrete value of their argument,
in case of @i{bound reference expression} these built-in calls deliver a
pointer to the previous or next element.

@i{ABS} is defined on numeric values, i.e. integer values and floating
point values, delivering the corresponding absolute value.

@i{LENGTH} is defined on

@itemize @bullet

@item string and text locations and string expressions, delivering the
length of them;

@item event locations, delivering the @b{event length} of the mode of the
location;

@item buffer locations, delivering the @b{buffer length} of the mode of
the location;

@item string mode names, delivering the @b{string length} of the mode;

@item text mode names, delivering the @b{text length} of the mode;

@item buffer mode names, delivering the @b{buffer length} of the mode;

@item event mode names, delivering the @b{event length} of the mode;

@item Additionally, @i{LENGTH} also may be used on the left hand
side of an assignment to set a new length of a @i{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 @b{RANGEFAIL} exception will be generated.
@end itemize

@i{SIN} delivers the sine of its argument (interpreted in radians).

@i{COS} delivers the cosine of its argument (interpreted in radians).

@i{TAN} delivers the tangent of its argument (interpreted in radians).

@i{ARCSIN} delivers the sin -1 function of its argument.

@i{ARCCOS} delivers the cos -1 function of its argument.

@i{ARCTAN} delivers the tan -1 function of its argument.

@i{EXP} delivers the exponential function, where x is the argument.

@i{LN} delivers the natural logarithm of its argument.

@i{LOG} delivers the base 10 logarithm of its argument.

@i{SQRT} delivers the sqare root of its argument.

@i{QUEUE_LENGTH} delivers either the number of sending delayed processes
plus the number of messages in a buffer queue (if the argument is a
@i{buffer location}), or the number of delayed processes (if the
argument specifies an @i{event location}) as @i{integer expression}.

@i{GEN_INST} delivers an @i{instance expression} constructed from the
arguments. Both arguments must have the @i{&INT}-derived class.

@i{COPY_NUMBER} delivers as @i{&INT}-derived class the copy number of an
@i{instance location}.

@i{GEN_PTYPE} delivers as @i{&INT}-derived class the associated number
of the @i{process name}.

@i{PROC_TYPE} delivers as @i{&INT}-derived class the process type of an
@i{instance expression}.

@i{GEN_CODE} delivers as @i{&INT}-derived class the associated number of
the @i{process name} or @i{signal name}.

@i{DESCR} delivers a @i{free reference expression} pointing to a
structure with the following layout describing the @i{location} argument.

@example
SYNMODE __tmp_descr = STRUCT (p PTR, l ULONG);
@end example


@item 7.4.2 Associating an outside world object@*
The syntax of the associate built-in routine call is defined as:

@example
@i{<associate built-in routine call> ::=}
@example
@i{ASSOCIATE ( <association location>, <string expression>,} [@i{, <string expression>} ] @i{)}
@end example
@end example

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.


@item 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.


@item 7.4.5 Modifying association attributes@*
The syntax of the MODIFY built-in routine call is defined as:

@example
@i{<modify built-in call> ::=}
@example
@i{MODIFY ( <association location>, <string expression> )}
@end example
@end example

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.


@item 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.


@item 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. 



@item 7.5.3 Text transfer operations@*
The syntax of @i{<text argument>} is changed to:

@example
@i{<text argument> ::=}
@example
  @i{<text location>}
| @i{<predefined text location>}
| @i{<varying string location>}
@end example

@i{<predefined text location> ::=}
@example
  STDIN
| STDOUT
| STDERR
@end example
@end example

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.



@item 7.5.5 Conversion@*
Due to the implementation of @i{<floating point modes>} the syntax
is changed to:

@example
@i{<conversion clause> ::=}
@example
@i{<conversion code> @{ <conversion qualifier @} *}
@i{[ <clause width> ]}
@end example

@i{<conversion code> ::=}
@example
@i{B} | @i{O} | @i{H} | @i{C} | @i{F}
@end example

@i{<conversion qualifier> ::=}
@example
@i{L} | @i{E} | @i{P<character>}
@end example

@i{<clause width> ::=}
@example
  @i{@{ <digit> @} +} | @i{V}
| @i{<real clause width>}
@end example

@i{<real clause width> ::=}
@example
@i{@{ @{ <digit> + | V @} : @{ @{ <digit> @} + | V @}}
@end example
@end example

Note: The @i{<real clause width>} is only valid for @i{<conversion
code>} `C' or `F'.


@item 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:
@table @samp
@item /
Write next record (record, line feed)

@item +
Write record on next page (form feed, record, line feed)

@item -
Write record on current line (record, carriage return)

@item ?
Write record as a prompt (carriage return, record)

@item !
Emit record (record).

@item =
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.
@end table

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.




@item 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.

@item 11.5 Signal definition statement@*
The @i{<signal definition statement>} may only occur at module level.

@item 12.3 Case Selection@*
The syntax of @i{<case label specification>} is changed to:

@example
@i{<case label specification> ::=}
@example
@i{( <case label> @{, <case label> @} * )}
@end example

@i{<case label> ::=}
@example
  @i{<discrete literal expression>}
| @i{<literal range>}
| @i{<discrete mode name>}
| @b{ELSE}
@end example
@end example

@end itemize

@node Directives
@chapter Compiler Directives

@itemize @bullet

@item ALL_STATIC_ON, ALL_STATIC_OFF@*
These directives control where procedure local variables are
allocated. ALL_STATIC_ON turns allocation of procedure local variables
in the data space ON, regardless of the keyword STATIC being used or not.
ALL_STATIC_OFF places procedure local variables in the stack space.
The default is ALL_STATIC_OFF.

@item RANGE_ON, RANGE_OFF@*
Turns generation of rangecheck code ON and OFF.

@item USE_SEIZE_FILE <character string literal>@*
Specify the filename (as a character string literal) where 
subsequent SEIZE statements are related to. This directive 
and the subsequent SEIZEs are written
to a possibly generated grant file for this module.

@example
<> USE_SEIZE_FILE "foo.grt" <>
SEIZE bar;
@end example

@item USE_SEIZE_FILE_RESTRICTED "filename"@*
Same as USE_SEIZE_FILE. The difference is that this directive
and subsequent SEIZEs are *not* written to a possibly generated
grant file. 

@item PROCESS_TYPE = <integer expression>@*
Set start value for all PROCESS delclarations. This value automatically
gets incremented after each PROCESS declaration and may be changed with
a new PROCESS_TYPE compiler directive.

@item SIGNAL_CODE = <integer expression>@*
Set start value for all SIGNAL definitions. This value automatically
gets incremented after each SIGNAL definition and may be changed with a
new SIGNAL_CODE compiler directive.

@item SEND_SIGNAL_DEFAULT_PRIORITY = <integer expression>@*
Set default priority for send signal action.

@item SEND_BUFFER_DEFAULT_PRIORITY = <integer expression>@*
Set default priority for send buffer action.

Note: Every <integer expression> in the above mentioned compiler
directives may also be specified by a SYNONYM of an integer type.

@example
SYN first_signal_code = 10;
<> SIGNAL_CODE = first_signal_code <>
SIGNAL s1;
@end example

@end itemize

@node References
@chapter Language Definition References

@itemize @bullet
@item   CCITT High Level Language (CHILL) Recommendation Z.200
        ISO/IEC 9496, Geneva 1989                ISBN 92-61-03801-8

@item   An Analytic Description of CHILL, the CCITT high-level
        language, Branquart, Louis & Wodon, Springer-Verlag 1981
                                                 ISBN 3-540-11196-4

@item   CHILL User's Manual
        CCITT, Geneva 1986                       ISBN 92-61-02601-X

@item   Introduction to CHILL
        CCITT, Geneva 1983                       ISBN 92-61-017771-1

@item   CHILL CCITT High Level Language
        Proceedings of the 5th CHILL Conference
        North-Holland, 1991                      ISBN 0 444 88904 3

@item   Introduction to the CHILL programming Language
        TELEBRAS, Campinas, Brazil 1990

@end itemize

Z.200 is mostly a language-lawyer's document, but more readable
than most.  The User's Guide is more readable by far, but doesn't
cover the whole language.  Our copies of these documents came through
Global Engineering Documents, in Irvine, CA, USA. (714)261-1455.

@bye