Language Reference/Facts - Revision history

Thomas Linder Puls: release

2019-03-12T16:16:19Z

release

← Older revision		Revision as of 18:16, 12 March 2019
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	=== Constant fact variable ===		=== Constant fact variable ===

	~~{{Template:NonReleased}}~~

	A constant fact variable is a fact variable that never changes value after it has been initialized. It can for example be a global "table" that initialized at some point and then used for lookup afterwards. Or an "id" in an object identifying what the object represents.		A constant fact variable is a fact variable that never changes value after it has been initialized. It can for example be a global "table" that initialized at some point and then used for lookup afterwards. Or an "id" in an object identifying what the object represents.

Thomas Linder Puls: release

2019-03-12T16:16:04Z

release

← Older revision		Revision as of 18:16, 12 March 2019
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	If the initialization expression can be evaluated to a constant at compile time then the fact is initialized immediately, rather than '''late'''.		If the initialization expression can be evaluated to a constant at compile time then the fact is initialized immediately, rather than '''late'''.

	~~{{Template:NonReleased}}~~

	Late initialization of facts is threadsafe in the following way: if two or more threads are reading a late fact simultaneously, they will/may potentially all execute the initialization code. But only '''''one''''' of the results will be used as the initial value, and all the threads will receive '''''that''''' value; all the other calculated initialization values will be discarded.		Late initialization of facts is threadsafe in the following way: if two or more threads are reading a late fact simultaneously, they will/may potentially all execute the initialization code. But only '''''one''''' of the results will be used as the initial value, and all the threads will receive '''''that''''' value; all the other calculated initialization values will be discarded.

Thomas Linder Puls: late fact atomic initialization

2019-02-21T13:27:06Z

late fact atomic initialization

← Older revision		Revision as of 15:27, 21 February 2019
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	If the initialization expression can be evaluated to a constant at compile time then the fact is initialized immediately, rather than '''late'''.		If the initialization expression can be evaluated to a constant at compile time then the fact is initialized immediately, rather than '''late'''.

			{{Template:NonReleased}}

			Late initialization of facts is threadsafe in the following way: if two or more threads are reading a late fact simultaneously, they will/may potentially all execute the initialization code. But only '''''one''''' of the results will be used as the initial value, and all the threads will receive '''''that''''' value; all the other calculated initialization values will be discarded.

	The attribute <vp>immediate</vp> can be used to enforce immediate initialization of a fact variable.		The attribute <vp>immediate</vp> can be used to enforce immediate initialization of a fact variable.

Thomas Linder Puls: constant facts

2019-02-19T15:39:41Z

constant facts

@@ Line 99: / Line 99: @@
 </vip>
-then the initialization expression will neer be evaluated, since the code never needed the value.
+then the initialization expression will never be evaluated, since the code never needed the value.
 The behavior of the code is very similar to this code:
@@ Line 148: / Line 148: @@
     ...
 end implement aaa_class</vip>
 }}

Thomas Linder Puls: released

2017-08-09T20:42:49Z

released

← Older revision		Revision as of 22:42, 9 August 2017
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	The idea of assigning <vp>erroneous</vp> value is to give clear runtime error if some code uses uninitialized fact variable by mistake.		The idea of assigning <vp>erroneous</vp> value is to give clear runtime error if some code uses uninitialized fact variable by mistake.

	~~{{Template:NonReleased}}~~

	Visual Prolog has '''late''' initialization of fact variables, meaning that the initialization code for a fact variable is not execute before and unless it is needed.		Visual Prolog has '''late''' initialization of fact variables, meaning that the initialization code for a fact variable is not execute before and unless it is needed.

Thomas Linder Puls: late fact initialization

2017-08-07T13:46:34Z

late fact initialization

@@ Line 52: / Line 52: @@
 <vipbnf><InitialValue> :
-    := <ConstantValue>
+    := <Term>
     := erroneous</vipbnf>
@@ Line 58: / Line 58: @@
     <LowerCaseIdentifier></vipbnf>
-A constant value <vpbnf><ConstantValue></vpbnf> should be a term (of the <vpbnf><Domain></vpbnf> type), which can be evaluated at compile time.
+The initialization expression <vpbnf><InitialValue></vpbnf> must evaluate to a value of <vpbnf><Domain></vpbnf> type.
-The constant value can be omitted only if the fact variable is initialized in a constructor. Class fact variables should always have an initial constant value.
+The initialization expression can be omitted (only) if the fact variable is initialized in a constructor. Class fact variables should always have an initialization expression.
-Notice that the keyword <vp>erroneous</vp> can be used as value to be assigned to fact variables. That is both lines below are valid:
+The keyword <vp>erroneous</vp> can be used as value to be assigned to fact variables. That is both lines below are valid:
 <vip>facts
@@ Line 70: / Line 70: @@
 The idea of assigning <vp>erroneous</vp> value is to give clear runtime error if some code uses uninitialized fact variable by mistake.
 === Facts ===

Thomas Linder Puls: /* Fact Declarations */ spelling

2015-03-28T14:29:40Z

Fact Declarations: spelling

← Older revision		Revision as of 16:29, 28 March 2015
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	<vipbnf><FactFunctorDeclaration> :		<vipbnf><FactFunctorDeclaration> :
	<FactName> : ( <Argument>-comma-sep-list-opt ) <~~FfactMode~~>-opt</vipbnf>		<FactName> : ( <Argument>-comma-sep-list-opt ) <FactMode>-opt</vipbnf>

	<vipbnf><FactName> :		<vipbnf><FactName> :

Thomas Linder Puls: Consistency

2012-10-26T08:49:07Z

Consistency

← Older revision		Revision as of 10:49, 26 October 2012
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	{{languageReferenceNavbar\|Facts}}		{{languageReferenceNavbar\|Facts}}

			=== Facts Sections ===

	A <vp>facts</vp> section declares a fact database, consisting of a number of facts. The fact database and the facts belong to the current scope.		A <vp>facts</vp> section declares a fact database, consisting of a number of facts. The fact database and the facts belong to the current scope.

Thomas Linder Puls: Example Template

2008-11-05T10:12:14Z

Example Template

← Older revision		Revision as of 12:12, 5 November 2008
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	Facts can only be declared in a class implementation and subsequently they can only be referenced from this implementation. So the scope of facts is the implementation in which they are declared. But the lifetime of object facts is the lifetime of the object to which they belong. Likewise the lifetime of class facts are from program start to program termination.		Facts can only be declared in a class implementation and subsequently they can only be referenced from this implementation. So the scope of facts is the implementation in which they are declared. But the lifetime of object facts is the lifetime of the object to which they belong. Likewise the lifetime of class facts are from program start to program termination.

	~~'''~~Example~~'''~~		{{Example\| The following class declares an object fact <vp>objectFact</vp> and a class fact <vp>classFact</vp>:

	The following class declares an object fact <vp>objectFact</vp> and a class fact <vp>classFact</vp>:

	<vip>implement aaa_class		<vip>implement aaa_class
Line 84:		Line 82:
	...		...
	end implement aaa_class</vip>		end implement aaa_class</vip>
			}}

Thomas Linder Puls: header levels

2008-10-14T22:10:49Z

header levels

← Older revision		Revision as of 00:10, 15 October 2008
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	- <LowerCaseIdentifier></vipbnf>		- <LowerCaseIdentifier></vipbnf>

	== Fact Declarations ==		=== Fact Declarations ===

	A fact declaration declares a fact of a fact database. A fact declaration is either a fact variable, or a functor fact.		A fact declaration declares a fact of a fact database. A fact declaration is either a fact variable, or a functor fact.
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	If mode is <vp>nondeterm</vp>, then the fact can have zero, one, or any other number of values. If mode is <vp>determ</vp>, then the fact can have zero or one value. If fact has zero values, then any read access to it gives fail.		If mode is <vp>nondeterm</vp>, then the fact can have zero, one, or any other number of values. If mode is <vp>determ</vp>, then the fact can have zero or one value. If fact has zero values, then any read access to it gives fail.

	== Fact Variable Declarations ==		=== Fact Variable Declarations ===

	A fact variable is similar to a one-argument <vp>single</vp> functor fact. However, syntactically it is used as a mutable variable (i.e. with assignment).		A fact variable is similar to a one-argument <vp>single</vp> functor fact. However, syntactically it is used as a mutable variable (i.e. with assignment).
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	The idea of assigning <vp>erroneous</vp> value is to give clear runtime error if some code uses uninitialized fact variable by mistake.		The idea of assigning <vp>erroneous</vp> value is to give clear runtime error if some code uses uninitialized fact variable by mistake.

	== Facts ==		=== Facts ===

	Facts can only be declared in a class implementation and subsequently they can only be referenced from this implementation. So the scope of facts is the implementation in which they are declared. But the lifetime of object facts is the lifetime of the object to which they belong. Likewise the lifetime of class facts are from program start to program termination.		Facts can only be declared in a class implementation and subsequently they can only be referenced from this implementation. So the scope of facts is the implementation in which they are declared. But the lifetime of object facts is the lifetime of the object to which they belong. Likewise the lifetime of class facts are from program start to program termination.