Precise precedence

[Tjad Clark]

Hi

I am having precedence issues where I would like to control precisely how the precedence works.

Example

RULE_A
    //More specific than RULE_B (Larger)
;


RULE_B
    //Some rule also matched by RULE_A
;


RULE_C
    : RULE_B
    | RULE_A
;

I would like RULE_B to be matched instead of RULE_A and there is no way to differentiate RULE_B from RULE_A

So I tried to use gate predicates as follows

@members { boolean notB = true }

RULE_C
    : RULE_B {notB = false}
    | {notB}? RULE_A
;

However to my surprise, this didn't work as the action does not get executed.

This would mean the lexing is being done as a side process - only returning the matched rule, and thereafter executing the matched rule's action code. In other words it will run through RULE_B, then run through RULE_A, and return as RULE_A as that rule is more specific.

Is there a way to change the variable 'notB' (execute the action) during the lexing ?

[Terence Parr]

hi. try fragment keyword on A and B.

Ter

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[Tjad Clark]

Perfect! Thanks a million!! :)

Hmmm.. Will need to read up on that section again

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