LALR parser generator: Difference between revisions

Revision as of 08:54, 8 November 2015

Revision as of 22:57, 23 January 2017

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An '''LALR parser generator''' is a software tool that reads a [[BNF grammar]] and creates an [[LALR parser]] which is capable of parsing files written in the [[computer language]] defined by the BNF grammar. [[LALR parser]]s are desirable because they are very fast and small in comparison to other types of parsers.

There are other types of [[parser generator]]s, such as SLR, LR, GLR, LL and LLGLL parser generators. What differentiates one from another is the type of BNF grammar which they are capable of accepting and the type of parsing algorithm which is used in the generated parser. An LALR parser generator accepts an LALR grammar as input and generates a parser that uses an LALR parsing algorithm (which is driven by LALR parser tables).

In practice, LALR offers a good solution, because LALR(1) grammars are more powerful than SLR(1), and can parse most practical LL(1) grammars. LR(1) grammars are more powerful than LALR(1), however, canonical LR(1) parsers can be extremely large in size and are considered not practical. Minimal LR(1) parsers are small in size and comparable to LALR(1) parsers.