parsil-peg 0.1.1

A lightweight PEG parser combinator library for Python.

Parsil

A lightweight PEG parser combinator library for Python.

Parsil provides a small set of composable parsing rules for building recursive-descent parsers. It is designed to be simple, readable, and easy to extend.

Features

• Lightweight and dependency-free
• PEG-style parser combinators
• Recursive grammars
• Regular expression support
• Rule composition with operators
• Rule transformation with Map
• Structured parsing results (Success / Failure)
• Full-input parsing
• Helpful parse error reporting

Installation

Install from PyPI:

pip install parsil-peg

Or install the latest development version from source:

git clone https://github.com/shahilahmed/parsil.git
cd parsil
pip install -e .

Quick Start

from parsil import *

grammar = Grammar()

grammar["number"] = R(r"\d+").map(int)

parser = Parser(grammar, "123")

result = parser.parse("number")

if result.ok:
    print(result.value)

Output:

123

Building Grammars

Parsil supports a concise DSL for composing parser rules.

Expression	Equivalent
a + b	Sequence(a, b)
a | b	Choice(a, b)
rule.star()	Repeat(rule)
rule.plus()	Repeat(rule, minimum=1)
rule.optional()	Repeat(rule, maximum=1)
rule.map(func)	Map(rule, func)

Helper functions:

Function	Equivalent
L(text)	Literal(text)
R(pattern)	Regex(pattern)
Ref_(name)	Ref(name)

Example

from parsil import *

grammar = Grammar()

grammar["word"] = (
    L("hello")
    + L(" ")
    + L("world")
)

parser = Parser(grammar, "hello world")

result = parser.parse("word")

if result.ok:
    print(result.value)

Output:

['hello', ' ', 'world']

Parse Results

Every parse returns either a Success or Failure.

Successful parse:

result = parser.parse("number")

if result.ok:
    print(result.value)

Failed parse:

result = parser.parse("number")

if result.failed:
    print(result.position)
    print(result.expected)

Example:

Failure(position=4, expected=[')'])

Available Rules

Rule	Description
Literal	Match an exact string
Regex	Match a regular expression
Sequence	Match rules in order
Choice	Match the first successful rule
Repeat	Match a rule repeatedly
Ref	Reference another grammar rule
Map	Transform a matched value

Project Structure

parsil/
├── examples/
├── parsil/
│   ├── grammar.py
│   ├── parser.py
│   ├── result.py
│   └── rules/
│       ├── base.py
│       ├── literal.py
│       ├── regex.py
│       ├── sequence.py
│       ├── choice.py
│       ├── repeat.py
│       ├── ref.py
│       └── map.py
├── tests/
├── LICENSE
├── README.md
└── pyproject.toml

Running Tests

pytest

Requirements

• Python 3.8 or later

License

This project is licensed under the MIT License.

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PyPI

https://pypi.org/project/parsil-peg/

Source Code

https://github.com/shahilahmed/parsil