Parglare

A pure Python scannerless LR/GLR parser.

For more information see the docs.

Quick intro

This is just a small example to get the general idea. This example shows how to parse and evaluate expressions with 5 operations with different priority and associativity. Evaluation is done using semantic/reduction actions.

The whole expression evaluator is done in under 30 lines of code!

from parglare import Parser, Grammar

grammar = r"""
E: E '+' E  {left, 1}
 | E '-' E  {left, 1}
 | E '*' E  {left, 2}
 | E '/' E  {left, 2}
 | E '^' E  {right, 3}
 | '(' E ')'
 | number;

terminals
number: /\d+(\.\d+)?/;
"""

actions = {
    "E": [lambda _, n: n[0] + n[2],
          lambda _, n: n[0] - n[2],
          lambda _, n: n[0] * n[2],
          lambda _, n: n[0] / n[2],
          lambda _, n: n[0] ** n[2],
          lambda _, n: n[1],
          lambda _, n: n[0]],
    "number": lambda _, value: float(value),
}

g = Grammar.from_string(grammar)
parser = Parser(g, debug=True, actions=actions)

result = parser.parse("34 + 4.6 / 2 * 4^2^2 + 78")

print("Result = ", result)

# Output
# -- Debugging/tracing output with detailed info about grammar, productions,
# -- terminals and nonterminals, DFA states, parsing progress,
# -- and at the end of the output:
# Result = 700.8

Installation

• Stable version:

  $ pip install parglare
  

• Development:

  Install just.

  $ git clone git@github.com:igordejanovic/parglare.git
  $ cd parglare
  $ just dev
  

Citing parglare

If you use parglare in your research please cite this paper:

Igor Dejanović, Parglare: A LR/GLR parser for Python,
Science of Computer Programming, issn:0167-6423, p.102734,
DOI:10.1016/j.scico.2021.102734, 2021.

@article{dejanovic2021b,
    author = {Igor Dejanović},
    title = {Parglare: A LR/GLR parser for Python},
    doi = {10.1016/j.scico.2021.102734},
    issn = {0167-6423},
    journal = {Science of Computer Programming},
    keywords = {parsing, LR, GLR, Python, visualization},
    pages = {102734},
    url = {https://www.sciencedirect.com/science/article/pii/S0167642321001271},
    year = {2021}
}

License

MIT

Python versions

Tested with 3.8-3.14

Credits

Initial layout/content of this package was created with Cookiecutter and the audreyr/cookiecutter-pypackage project template.