shift/reduce problem

["yuntao" <yuntao@eventmonitor.com>]

Hi,

 

I am using sablecc to parse some if statements, the grammar is as follows:

 

  if_statement =
   {if} if general_expression then [true]:statement |
   {if_else} if general_expression then [true]:statement else statement;

 

After run SableCC, I got the following error message:

 

     [exec] shift/reduce conflict in state [stack: TIf PGeneralExpression TThen
PStatement *] on TElse in {
     [exec]     [ PIfStatement = TIf PGeneralExpression TThen PStatement * TElse
 PStatement ] (shift),
     [exec]     [ PIfStatement = TIf PGeneralExpression TThen PStatement * ] fol
lowed by TElse (reduce)
     [exec]

 

The message basically says that there is a reduce/shift conflict after it sees the

keyword "else". I would like the code behaving do shift first. Any suggestion?

 

Also I look at simplecc.sablecc sample, it looks like they have similar grammar to

define the "if" statements, just wondering how they can avoid the problem.

 

Thanks a lot.

 

Yuntao Cui