Chevrotain

LL(K) Grammars

Chevrotain can be used to build parsers for LL(K)open in new window Grammars. This means that the number of lookahead tokens needed to disambiguate two alternatives must be a fixed number and known in advance.

For example given the grammar

statement:
   A B C |
   A B D |
   A B E

Chevrotain will look three tokens ahead to decide between the two alternatives.

But given the following grammar

statement:
   longRule B  |
   longRule C  |
   longRule D

longRule:
   A+

Chevrotain will throw a an error during the parser initialization in this case. This is because there is no fixed number of tokens we can use to choose between the alternatives that is due to a potentially infinite number of "A" tokens that can appear before the "B" - "C" tokens.