Ambiguous call expression in ANTLR4 grammar

Question

I have a simple grammar (for demonstration)

grammar Test;


program
    :   expression* EOF
    ;


expression
    :   Identifier
    |   expression \'(\' ex         


        

Answer 1

The solution to this is to temporary "unhide" whitespace in your second alternative. Have a look at this question for how this can be done.

With that solution your code could look somthing like this

expression
    :   Identifier
    |   {enableWS();} expression '(' {disableWS();} expression? ')'
    |   '(' expression ')'
    ;

That way the second alternative matches the input WS-sensitive and will therefore only be matched if the identifier is directly followed by the bracket.

See here for the implementation of the MultiChannelTokenStream that is mentioned in the linked question.