Barrett G.Occam 3 reference manual.1992
.pdf
I Invalid processes
Processes which become invalid during program execution may behave in one of three ways, determined by a compiler option. An invalid process may behave in one of these ways: the process may stop, the system may halt, or the behaviour of the process may be undefined.
The three modes of existence in detail are:
Stop process mode In this mode, processes which become invalid behave like the primitive process STOP, thus allowing other processes to continue. The invalid process stops, and in particular does not make erroneous outputs to other processes. Other processes continue until they become dependent upon data from the stopped process. In this mode it is therefore possible to write communications which will timeout to warn of a stopped process, and to construct a system with redundancy in which a number of processes performing the same task may be used to enable the system to continue after one of the processes has failed.
Halt system mode In this mode an invalid process may cause the whole system to halt, and is useful for the development of programs, particularly when debugging concurrent systems. In this mode the primitive process STOP will also cause the whole system to halt.
Undefined mode In this mode, an invalid process may have an arbitrary effect, and is only useful for optimising programs known to be correct!
DRAFT --- March 31, 1992
J Syntax summary
J.1 |
Collected syntax |
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J.1.1 |
Assignment |
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assignment |
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variable.list := expression.list |
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expression.list |
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name ( 0 , expression ) |
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1 , expression |
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( value.process |
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) |
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variable.list |
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1 , variable |
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J.1.2 |
Replicator |
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replicator |
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name = base FOR count |
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base |
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expression |
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count |
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expression |
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J.1.3 |
Process constructions |
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sequence |
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SEQ |
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process |
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SEQ replicator |
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process |
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conditional |
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IF |
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choice |
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IF replicator |
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choice |
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choice |
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guarded.choice |
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conditional |
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specification |
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choice |
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guarded.choice |
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boolean |
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process |
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DRAFT --- March 31, 1992
selection
selector
option
case.expression
loop
parallel
alternation
alternative
guarded.alternative
variant
CASE selector |
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option |
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expression
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1 , case.expression |
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process |
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| ELSE process
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expression
WHILE boolean |
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process |
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PAR |
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process |
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| PAR replicator process
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ALT |
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alternative |
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ALT replicator |
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alternative |
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guarded.alternative |
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alternation |
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channel ? CASE |
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variant |
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boolean & channel ? CASE |
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variant |
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specification |
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alternative |
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guard |
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process |
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specification |
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variant |
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tagged.list |
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process |
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specification |
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variant |
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DRAFT --- March 31, 1992
guard
discrimination
discriminant
process
specification
J.1.4 Data types
data.type
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input |
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boolean & input |
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boolean & SKIP |
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ACCEPT call.channel ( , call.formal |
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process |
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boolean & ACCEPT call.channel ( , |
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process |
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GRANT channel |
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process |
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boolean & GRANT channel |
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process |
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CASETAG expression |
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discriminant |
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name |
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process |
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SKIP |
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STOP |
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specification |
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process |
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declaration |
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abbreviation |
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definition |
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EXPORT |
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export.item |
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FROM |
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specification |
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BOOL |
BYTE |
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INT |
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INT16 |
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INT32 |
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INT64 |
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REAL32 |
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REAL64 |
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NONE |
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[ expression ] data.type |
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name |
)
call.formal )
DRAFT --- March 31, 1992
definition
structured.type
field.name
specifier
J.1.5 Values
abbreviation
J.1.6 Variables
variable
declaration
abbreviation
J.1.7 Channels
channel.type
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DATA TYPE name IS data.type : |
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DATA TYPE name |
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structured.type |
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RECORD |
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data.type 1, field.name : |
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UNION |
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data.type 1, name : |
name
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data.type |
[]specifier |
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[ expression ]specifier |
VAL name IS expression :
| VAL specifier name IS expression :
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variable[name] |
[ variable FROM base FOR count ] |
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[ variable FOR count ] |
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[ variable FROM base ] |
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variable[expression] |
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data.type 1 , name : |
INITIAL data.type name IS expression : |
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name IS variable : |
| specifier name IS variable : |
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RESULT name IS variable : |
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RESULT specifier name IS variable : |
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CHAN OF protocol |
name |
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[expression]channel.type |
DRAFT --- March 31, 1992
channel
declaration
abbreviation
input
input.item
tagged.list
variant
output
output.item
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name |
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channel[expression] |
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[channel FROM base FOR count] |
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[channel FROM base ] |
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[channel FOR count] |
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[ 1, channel ] |
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[CHAN replicator : channel] |
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module[name] |
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channel.type 1, name : |
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name IS channel : |
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specifier name IS channel : |
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channel ? 1 ; input.item |
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channel ? CASE tagged.list |
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channel ? CASE |
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variant |
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variable |
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variable :: variable |
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tag |
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tag ; 1 ; input.item |
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specification |
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variant |
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tagged.list |
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process |
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specification |
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variant |
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channel ! 1 ; output.item |
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channel ! tag |
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channel ! tag ; 1 ; output.item |
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port ! expression |
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expression |
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expression :: expression |
DRAFT --- March 31, 1992
definition |
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CHAN TYPE name |
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RECORD |
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declaration |
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CHAN TYPE name |
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RECORD |
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declaration |
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PROTOCOL name |
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CASE |
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tagged.protocol |
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PROTOCOL name IS simple.protocol : |
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PROTOCOL name IS sequential.protocol : |
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protocol |
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name |
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simple.protocol |
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simple.protocol |
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data.type |
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data.type::[]data.type |
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sequential.protocol |
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1 ; simple.protocol |
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tagged.protocol |
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tag |
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tag ; sequential.protocol |
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tag
specifier
J.1.8 Call channels
call.channel
name
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channel.type |
[]specifier |
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[expression]specifier |
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name |
call.channel[expression] |
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[ 1, call.channel ] |
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[CALL replicator : call.channel ] |
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[ call.channel FROM base FOR count ] |
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[ call.channel FROM base ] |
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[ call.channel FOR count ] |
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module[name] |
DRAFT --- March 31, 1992
declaration
abbreviation
call.actual
call.formal
call.type
specifier
J.1.9 Sharing
declaration
shared.call
shared.channels
J.1.10 Timers
timer
declaration
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call.type name ( , call.formal ) : |
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name IS call.channel : |
specifier call.header IS call.channel : |
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expression |
variable |
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data.type 1 , name |
VAL data.type 1 , name |
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INITIAL data.type 1 , name |
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RESULT data.type 1 , name |
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CALL |
[expression]call.type |
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call.type |
[]specifier |
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[expression]specifier |
shared.call name ( 0, formal ) : | shared.channels name :
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SHARED CALL |
[expression]shared.call |
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SHARED name |
[expression]shared.channels |
name
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timer[expression] |
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[timer FROM base FOR count] |
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[timer FROM base] |
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[timer FOR count] |
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timer.type 1, name : |
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DRAFT --- March 31, 1992
abbreviation
timer.type
timer.input
delayed.input
specifier
J.1.11 Expressions
boolean byte
expression
operand
valof
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name IS timer : |
specifier name IS timer : |
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[expression]timer.type |
TIMER |
timer ? variable
timer ? AFTER expression
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timer.type |
[]specifier |
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[expression]specifier |
expression
’character’
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operand |
monadic.operator operand |
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operand dyadic.operator operand |
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MOSTPOS data.type |
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MOSTNEG data.type |
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expression[name] |
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conversion |
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WIDTHOF (data.type) |
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variable |
literal |
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table |
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(expression) |
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( value.process |
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name ( 0 , expression ) |
specification valof
DRAFT --- March 31, 1992
literal
table
conversion
digit
exponent
hex.digit
integer
real
decoration
J.1.12 Procedures
definition
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integer |
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byte |
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integer(decoration) |
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byte(decoration) |
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real(decoration) |
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string |
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TRUE | FALSE |
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[](NONE) |
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[ 1 , expression |
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[ , expression |
](decoration) |
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[VAL replicator : expression] |
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( name :- expression ) (decoration) |
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table [ subscript ] |
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[ 1 , expression |
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[ table FROM subscript FOR count ] |
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[ table FROM subscript ] |
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[ table FOR count ] |
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data.type operand |
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data.type ROUND operand |
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data.type TRUNC operand |
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0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9
+digits | -digits
digit | A | B | C | D | E | F
digits | #hex.digits
digits.digits | digits.digits Eexponent
data.type
PROC name ( 0 , formal ) |
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process |
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DRAFT --- March 31, 1992