peco

This is a tiny (100 LOC) parser combinator library in Python.

Installation:

pip install pecolib

Main features:

• Combined lexical and syntactic parsing using the PEG formalism.
• Lexical rules with regular expressions (see eat).
• Stack-based implementation of semantic actions (see push and to).
• Selective memoization for performance (see memo).
• Support for left recursion (see left).

Parsers are built from combinators and operate on a Peco namedtuple:

• text: str. Source text.
• pos: int. Position in the text.
• ok: bool. Parsing result.
• stack: tuple | None. Semantic result stack.
• glob: dict. Global data, including the error position field (err).

Most combinators follow PEG constructs:

• empty. Empty string.
• seq. Sequence.
• alt. Ordered choice.
• many. Zero-or-more.
• some. One-or-more.
• opt. Optional.
• peek. And-predicate.
• npeek. Not-predicate.

Support for semantic actions:

• push(f). Pushes a text fragment parsed by the f combinator onto the stack.
• to(f). Pops n elements from the stack and passes them as arguments to function f with arity n. The result is pushed back onto the stack.
• group(f). Combines all elements pushed onto the stack by f into a single tuple.

For examples of using peco's combinators, see the tests.