A pure Python scannerless LR/GLR parser.
For more information see the docs.
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- Stable version:
$ pip install parglare- Development version:
$ git clone git@github.com:igordejanovic/parglare.git
$ pip install -e parglareIf 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}
}
MIT
Tested with 3.6-3.11
Initial layout/content of this package was created with Cookiecutter and the audreyr/cookiecutter-pypackage project template.