Using first-set in recursive descent parser

I'm writing a recursive descent parser for C in C++. I don't know how to choose the right production in the following case:

statement: labeled-statement | compound-statement | expression-statement | selection-statement | iteration-statement | jump-statement

I read about the "first"-set which compares the lookahead-token/char with possible terminals which comes first in the productions. Currently I'm stuck at using a first-set in a recursive descent parser, because I only have a function and nothing else, no object for each ru开发者_JAVA技巧le or anything else with which I can identify a rule/production.

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Your grammar is invalid for recursive descent parsers because it's ambiguous on the left side:

• labeled-statement starts with an identifier
• compound-statement starts with a { (this is fine)
• expression-statement starts with an identifier or a number (or ()

Can stop here, you have a clash between labeled statement and expression statement. You need to transform your grammer to get rid of left-side ambiguities (through temporary grammar nodes to contain the common parts so when you branch you can determine which branch to go to using only the look-ahead).