Principle:Ggml org Llama cpp PEG Parser Framework
| Knowledge Sources | |
|---|---|
| Domains | Parsing, Grammar |
| Last Updated | 2026-02-15 00:00 GMT |
Overview
The PEG Parser Framework is the principle of using Parsing Expression Grammars to define and execute structured text parsers within llama.cpp.
Description
This principle provides a general-purpose PEG (Parsing Expression Grammar) parser implementation that can be used to define formal grammars and parse text against them. PEG grammars offer unambiguous parsing with ordered choice, making them well-suited for parsing model outputs, configuration formats, and structured text. The framework also includes partial regex matching capabilities for incremental text validation.
Usage
Apply this principle when you need to define formal grammars for parsing structured text, such as chat model output formats, or when incremental regex-based validation of partially generated text is required.
Theoretical Basis
Parsing Expression Grammars (PEGs) differ from context-free grammars in that the choice operator is ordered (prioritized), eliminating ambiguity. A PEG parser uses recursive descent with backtracking, attempting alternatives in order and committing to the first match. This makes PEGs particularly suitable for parsing programming languages and structured output formats. The partial regex component extends standard regex matching to handle incomplete strings, which is essential for validating text as it is being generated token by token during inference.