TOPIC:

Hello ,
I am getting Reduce -Reduce Conflict for the following grammar. How can I resolve it?

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Production Rules

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VariableRef ::= (VarIdentifier | ValueParIdentifier) [ExtendedFieldReference]

VarIdentifier ::= Identifier
ValueParIdentifier ::= Identifier

ExtendedFieldReference:=...........

---

As 'Identifier' is giving two production we will get this conflict. What is the way to resolve it?
I am using Yacc for the parsing.

regards,
Anil Krishna

Hi Anil,

this is one of the examples why I said earlier that then TTCN-3 BNF as given in the standard is not suitable as an implementation grammar. The grammar states that a VariableRef is either a VarId or a ValueParId, which are in turn both identifiers. From a context free grammar point of view, there is no easy way to distinguish between an id that refers to a variable and an id that refers to a value parameter - this is context sensitive information.

To solve this problem, you need to simplify the grammar, e.g., into

VariableRef ::= Identifier [ExtendedFieldReference]

and then at during the analysis phase of the compilation, e.g., during name resolving, determine what this particular id refers to.

Best regards

Stephan Tobies

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Original Message

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From: ext AnilKrishna [This email address is being protected from spambots. You need JavaScript enabled to view it.]
Sent: Wednesday, November 06, 2002 10:10 AM
To: This email address is being protected from spambots. You need JavaScript enabled to view it.
Subject: R-R Conflict


Hello ,
I am getting Reduce -Reduce Conflict for the following grammar. How can I resolve it?

---

Production Rules

---

VariableRef ::= (VarIdentifier | ValueParIdentifier) [ExtendedFieldReference]

VarIdentifier ::= Identifier
ValueParIdentifier ::= Identifier

ExtendedFieldReference:=...........

---

As 'Identifier' is giving two production we will get this conflict. What is the way to resolve it?
I am using Yacc for the parsing.

regards,
Anil Krishna

Hello Anil,

the point is you can not resolve this problem. Stephan mentioned already
before that you have to modify your grammar in order to be able to write
a parser. This is an example of the issues.

The question whether an identifier is a variable identifier or a
parameter identifier can not be decided with a context free grammar. In
fact you need a context in order to be able to answer this questions.

Best regards,

Theo

AnilKrishna schrieb:
> Hello ,
> I am getting Reduce -Reduce Conflict for the following grammar.
> How can I resolve it?
>
>

---

Production
> Rules

---

> VariableRef ::= (VarIdentifier | ValueParIdentifier)
> [ExtendedFieldReference]
>
> VarIdentifier ::= Identifier
> ValueParIdentifier ::= Identifier
>
> ExtendedFieldReference:=...........
>

---

---

>
> As 'Identifier' is giving two production we will get this conflict. What
> is the way to resolve it?
> I am using Yacc for the parsing.
>
> regards,
> Anil Krishna


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