LL(1)
In computer science, an LL parser is a top-down parser for a subset of context-free languages. It parses the input from Left to right, performing Leftmost derivation of the sentence.
An LL parser is called an LL(k) parser if it uses k tokens of lookahead when parsing a sentence. If such a parser exists for a certain grammar and it can parse sentences of this grammar without backtracking then it is called an LL(k) grammar. LL(k) grammars can generate more languages the higher the number k of lookahead tokens. A corollary of this is that not all context-free languages can be recognized by an LL(k) parser. An LL parser is called an LL(*) parser (an LL-regular parser) if it is not restricted to a finite k tokens of lookahead, but can make parsing decisions by recognizing whether the following tokens belong to a regular language (for example by means of a Deterministic Finite Automaton).
LL grammars, particularly LL(1) grammars, are of great practical interest, as parsers for these grammars are easy to construct, and many computer languages are designed to be LL(1) for this reason. LL parsers are table-based parsers, similar to LR parsers. LL grammars can also be parsed by recursive descent parsers.
For a given context-free grammar, the parser attempts to find the leftmost derivation. Given an example grammar :
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