Question 1

How does PEGTL compare to ANTLR for C++ parsing?

Accepted Answer

PEGTL is a header-only C++ library with grammars defined in code, offering more control and integration but requiring template expertise. ANTLR uses external grammar files and generates code, which can be easier for complex languages but adds dependencies and may have slower runtime performance. PEGTL is better for tight C++ integration, while ANTLR suits multi-language projects.

Question 2

How to handle errors and recovery in a PEGTL parser?

Accepted Answer

PEGTL provides mechanisms for error reporting through custom actions and states, but error recovery must be manually implemented by defining rules that catch failures and adjust parsing state. The library's grammar analysis helps prevent errors, but robust recovery requires careful design of action classes and control flow.

Question 3

What C++ version is needed for PEGTL?

Accepted Answer

PEGTL requires C++17 for the main branch and latest releases, as noted in the documentation. Older versions (2.x and 1.x) support C++11, but new features and improvements are only available in the C++17-compatible versions, so upgrading compilers might be necessary.

Question 4

Can PEGTL parse left-recursive grammars?

Accepted Answer

No, PEGTL does not support left recursion natively because it uses Parsing Expression Grammars (PEGs), which prohibit left recursion. The grammar analysis feature detects left recursion as an error, so users must rewrite grammars to eliminate it, often by using iterative or right-recursive rules.

Question 5

Are there performance benchmarks for PEGTL vs other libraries?

Accepted Answer

The README does not include specific benchmarks, but PEGTL emphasizes simplicity and efficiency, with compile-time optimizations. Performance is generally competitive for static grammars, but runtime parsing speed can vary based on action complexity; users should test with their specific use cases for accurate comparisons.

Question 6

How to build an abstract syntax tree (AST) with PEGTL?

Accepted Answer

To build an AST, you define custom action classes that are attached to grammar rules, creating nodes and relationships during parsing. The library provides examples, like the JSON parser, where actions construct data structures incrementally, but the design and implementation of the AST are entirely up to the user.

Question 7

Is PEGTL suitable for parsing very large files?

Accepted Answer

PEGTL can handle large files, but performance depends on grammar complexity and action efficiency. Since it's a single-pass parser with optional buffering, memory usage can be controlled, but for gigabyte-scale files, users may need to implement streaming or chunked parsing manually, as the library does not provide built-in support for this.

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