parglare 0.2

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[](https://coveralls.io/github/igordejanovic/parglare?branch=master)
[](http://igordejanovic.net/parglare/)
[](https://opensource.org/licenses/MIT)


A pure Python LR/GLR parser with integrated scanner.


For more information see [the docs](http://www.igordejanovic.net/parglare/).


## 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!

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

actions = {
"E": [lambda _, nodes: nodes[0] + nodes[2],
lambda _, nodes: nodes[0] - nodes[2],
lambda _, nodes: nodes[0] * nodes[2],
lambda _, nodes: nodes[0] / nodes[2],
lambda _, nodes: nodes[0] ** nodes[2],
lambda _, nodes: nodes[1],
lambda _, nodes: nodes[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
# -- Debuging/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
```

## Install

- Stable version:

```
$ pip install parglare
```

- Development version:

```
$ git clone git@github.com:igordejanovic/parglare.git
$ pip install -e parglare
```


## License

MIT

## Python versions

Tested with 2.7, 3.3-3.6

## Credits

Initial layout/content of this package was created with [Cookiecutter](https://github.com/audreyr/cookiecutter) and the [audreyr/cookiecutter-pypackage](https://github.com/audreyr/cookiecutter-pypackage) project template.


# History

- 2017-08-09 Version 0.2

- GLR parsing. Support for epsilon grammars, cyclic grammars and grammars with
infinite ambiguity.
- Lexical recognizers. Parsing the stream of arbitrary objects.
- Error recovery. Builtin default recovery, custom user defined.
- Common semantic actions.
- Documentation.
- pglr CLI command.
- Automata visualization, GLR visual tracing.
- Lexical disambiguation improvements.
- Support for epsilon grammar (empty productions).
- Support for comments in grammars.
- `finish` and `prefer` terminal rules.
- Change in the grammar language `=` - > `:`
- Additions to examples and tests.
- Various optimizations and bug fixes.

- 2017-02-02 - Version 0.1

- Textual syntax for grammar specification. Parsed with parglare.
- SLR and LALR tables calculation (LALR is the default)
- Scannerless LR(1) parsing
- Scanner is integrated into parsing. This give more power as the token
recognition is postponed and done in the parsing context at the current
parsing location.
- Declarative associativity and priority based conflict resolution for
productions
- See the `calc` example, or the quick intro bellow.
- Lexical disambiguation strategy.
- The default strategy is longest-match first and then `str` over `regex`
match (i.e. the most specific match). Terminal priority can be provided
for override if necessary.
- Semantic actions and default actions which builds the parse tree (controlled
by `actions` and `default_actions` parameters for the `Parser` class).
- If no actions are provided and the default actions are explicitely
disabled parser works as a recognizer, i.e. no reduction actions are
called and the only output of the parser is whether the input was
recognized or not.
- Support for language comments/whitespaces using special rule `LAYOUT`.
- Debug print/tracing (set `debug=True` and/or `layout_debug=True`to the
`Parser` instantiation).
- Tests
- Few examples (see `examples` folder)