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Conditional Statement Body [message #939363]

Wed, 10 October 2012 13:41

A Jaro
Messages: 3
Registered: October 2012

Junior Member

I am trying to set up the Xtext grammar file so it can parse a few different styles of conditional statements. There are two if statements that I am trying which are very common in programming languages today below.

The first one is pretty straight forward; left-curly braces around the body. The second one is where there isn't left-curly braces and only one line of body is allowed.

The else portion seems to be working fine, but I can't get the 'if' portion to generate properly. I continue to get the error (where the '...' is various functions):

Decision can match input such as "..." using multiple alternatives: 1, 2

if (expression)
{
     body
}
else
{
     body
}

if (expression)
     one-line body
else
     one-line body

Here is what I have for the grammar:

IfStatement:
	'if' parexpression+=Expression+ 
		((=>'{' (ifstatement+=Statement|declaration+=Declare)* '}') | 
				ifstatement+=Statement)
	(=>	'else' ((=>'{' (elsestatement+=Statement|declaration+=Declare)* '}')|
				(elsestatement+=Statement|declaration+=Declare))
		)?
;

How can I make this one work?

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Re: Conditional Statement Body [message #939605 is a reply to message #939363]

Wed, 10 October 2012 18:59

Henrik Lindberg
Messages: 2429
Registered: July 2009

Senior Member

One way is to make ExpressionBlock be an Expression.

Regards
- henrik

On 2012-10-10 19:41, A Jaro wrote:
> I am trying to set up the Xtext grammar file so it can parse a few
> different styles of conditional statements. There are two if statements
> that I am trying which are very common in programming languages today
> below.
> The first one is pretty straight forward; left-curly braces around the
> body. The second one is where there isn't left-curly braces and only
> one line of body is allowed.
>
> The else portion seems to be working fine, but I can't get the 'if'
> portion to generate properly. I continue to get the error (where the
> '...' is various functions):
>
> Decision can match input such as "..." using multiple alternatives: 1, 2
>
>
> if (expression)
> {
> body
> }
> else
> {
> body
> }
>
>
> or
>
>
> if (expression)
> one-line body
> else
> one-line body
>
>
>
> Here is what I have for the grammar:
>
>
> IfStatement:
> 'if' parexpression+=Expression+ ((=>'{'
> (ifstatement+=Statement|declaration+=Declare)* '}') |
> ifstatement+=Statement)
> (=> 'else' ((=>'{'
> (elsestatement+=Statement|declaration+=Declare)* '}')|
> (elsestatement+=Statement|declaration+=Declare))
> )?
> ;
>
>
> How can I make this one work?

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Re: Conditional Statement Body [message #939998 is a reply to message #939363]

Thu, 11 October 2012 04:06

Sebastian Zarnekow
Messages: 2788
Registered: July 2009

Senior Member

The problem could be caused the cardinality in the parexpression
assignment. You allow multiple expressions there. Is that intentional?

I'd go for

'if' parexpression=Expression

instead of

'if' parexpression=Expression+

Regards,
Sebastian
--
Looking for professional support for Xtext, Xtend or Eclipse Modeling?
Go visit: http://xtext.itemis.com

Am 10.10.12 19:41, schrieb A Jaro:
> I am trying to set up the Xtext grammar file so it can parse a few
> different styles of conditional statements. There are two if statements
> that I am trying which are very common in programming languages today
> below.
> The first one is pretty straight forward; left-curly braces around the
> body. The second one is where there isn't left-curly braces and only
> one line of body is allowed.
>
> The else portion seems to be working fine, but I can't get the 'if'
> portion to generate properly. I continue to get the error (where the
> '...' is various functions):
>
> Decision can match input such as "..." using multiple alternatives: 1, 2
>
>
> if (expression)
> {
> body
> }
> else
> {
> body
> }
>
>
> or
>
>
> if (expression)
> one-line body
> else
> one-line body
>
>
>
> Here is what I have for the grammar:
>
>
> IfStatement:
> 'if' parexpression+=Expression+ ((=>'{'
> (ifstatement+=Statement|declaration+=Declare)* '}') |
> ifstatement+=Statement)
> (=> 'else' ((=>'{'
> (elsestatement+=Statement|declaration+=Declare)* '}')|
> (elsestatement+=Statement|declaration+=Declare))
> )?
> ;
>
>
> How can I make this one work?

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Re: Conditional Statement Body [message #940489 is a reply to message #939998]

Thu, 11 October 2012 13:30

A Jaro
Messages: 3
Registered: October 2012

Junior Member

That seems like such a simple fix; to remove the cardinality. I thought I had added that for a specific reason, but it seems to work much better with your suggestion. Thank you very much for your help, you have saved me quite a bit of time.

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