 A "predictive parser" is a recursive descent parser that does not require backtracking.Predictive parsing is possible only for the class of LL("k") grammars, which are the context-free grammars for which there exists some positive integer "k" that allows a recursive descent parser to decide which production to use by examining only the next "k" tokens of input.The LL("k") grammars therefore exclude all ambiguous grammars, as well as all grammars that contain left recursion.