[antlr-interest] common prefix on Parser rules.

[jbb at acm.org]

>Hello, this is more a grammar design question but antlr related ;)
>
>Look:
>
>Supose I have the next grammar description:
>
>MemberExpresion: new  MemberExpression Arguments
>
>NewExpression: new NewExpression | MemberExpression
>
>
>Obviously the new prefix is causing a non-determinism escenario. Any
>suggestion for transforming this description to let antlr generate a
>correct parser?
>
>MemberExpression has others rules too, not just "new MemberExpression
>Arguments".

[I assume that you meant MemberExpression on the lhs of the first rule above]
                                    ^^

Note that this is *not* a grammar design question but rather is a
question of how to transform a grammar into proper LL(k) form (for
some finite value of k).

Observe that:

NewExpression: new NewExpression | MemberExpression

is equivalent to (unless there are also other NewExpression rules you
didn't tell us about):

NewExpression: ( new )* MemberExpression


Thus we now have

MemberExpression: new  MemberExpression Arguments ;
NewExpression: ( new )* MemberExpression ;

which is the same as

MemberExpression: ( new )+  MemberExpression Arguments ;
NewExpression: MemberExpression ;

You said that there are other MemberExpression rules so this result
may not be of any use to you...
-- 
	-jbb
----------------+----------------------------
 John B. Brodie | Email : jbrodie at cs.fit.edu
----------------+----------------------------

 

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