5.8.2. Directed Formal Parameters

5.8.2. Directed Formal Parameters
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	Description
	Directed formal parameters define the interface of a GT rule or an ASM rule by a list of ASM variables.

Syntax

	Syntax
DirectedFormalParamsAST ::= DirectionKindAST VariableDefAST \| DirectedFormalParamsAST , DirectionKindAST VariableDefAST DirectionKindAST ::= in \| out \| inout Directed formal parameters are defined by is a comma-separated list of variables (each having a direction specification). It can contain an arbitrary number of variables (including none). In contrast to the formal parameters, it defines a direction for each parameter, namely either `in`, `out` or `inout`.

	DirectedFormalParamsAST ::= DirectionKindAST VariableDefAST 
	                          | DirectedFormalParamsAST , DirectionKindAST VariableDefAST

	DirectionKindAST ::= in | out | inout

Directed formal parameters are defined by is a comma-separated list of variables (each having a direction specification). It can contain an arbitrary number of variables (including none). In contrast to the formal parameters, it defines a direction for each parameter, namely either in, out or inout.

Semantics

	Semantics
An input-only variable (with tag `in`) takes the value of the actual parameter, but at the end of the execution of the rule the value of the actual parameter is not updated. An output-only variable(with tag `out`) does not take the value of the actual parameter: it is considered as undefined having the undefined value (`undef`). At the end of the execution of the rule, the value of the actual parameter is overwritten with the value of the variable defined as formal parameter. An input-output variable(with tag `inout`) takes the value of the actual parameter, and at the end of the execution of the rule the value of the actual parameter is updated with the value of the variable defined as formal parameter.

An input-only variable (with tag in) takes the value of the actual parameter, but at the end of the execution of the rule the value of the actual parameter is not updated.

An output-only variable(with tag out) does not take the value of the actual parameter: it is considered as undefined having the undefined value (undef). At the end of the execution of the rule, the value of the actual parameter is overwritten with the value of the variable defined as formal parameter.

An input-output variable(with tag inout) takes the value of the actual parameter, and at the end of the execution of the rule the value of the actual parameter is updated with the value of the variable defined as formal parameter.

Used By: GT rule definition, ASM rule definition

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5.8.1. Formal Parameters	Home	5.8.3. Actual Parameters