Compilers/Parsers

Earley v/s PEG parsers

Earley and PEG parsers are two different parsing algorithms with some similarities and differences.

Earley parser is a general-purpose parsing algorithm that can parse any context-free grammar. It uses a dynamic programming technique to predict, scan, and complete input tokens to construct a parse tree. Earley parser can handle ambiguous grammars and provides the most expressive power, but it can also be slow for large grammars or inputs.

PEG (Parsing Expression Grammar) parser, on the other hand, is a top-down parsing algorithm that matches input against a set of parsing expressions, which are similar to regular expressions but with more features. PEG parser prioritizes parsing rules and avoids ambiguities by always choosing the first matching rule. PEG parsers can be fast and efficient for parsing structured text, but they may not be suitable for complex grammars that require backtracking or lookahead.

Here are some key differences between Earley and PEG parsers:

Earley parser can handle arbitrary context-free grammars, whereas PEG parser can only handle a subset of context-free grammars that are deterministic and unambiguous.
Earley parser uses a bottom-up parsing approach, whereas PEG parser uses a top-down parsing approach.
Earley parser can handle ambiguity by constructing multiple parse trees, whereas PEG parser resolves ambiguity by prioritizing rules and not backtracking.

In summary, Earley parser is more general and powerful but can be slower and more memory-intensive than PEG parser. PEG parser is more limited in scope but can be faster and easier to use for certain types of parsing tasks.