A parser combinator and formatter combinator library that's easy to use and that provides informative error messages.

## Project description

Parcon is a parser combinator library. It can be used for parsing both normal text and binary data. It’s designed to be easy to use and to provide informative error messages.

Pargen, which is provided as a submodule of Parcon, is a formatter combinator library. It’s much the opposite of Parcon: while Parcon is used to parse text into various objects, Pargen is used to format objects into text. As an example, if you wanted to reimplement Python’s json module, you would use Parcon to implement json.loads and Pargen to implement json.dumps.

All of the classes, and most of the functions, in Parcon are comprehensively documented. The best place to look for help is in Parcon’s module documentation.

Here’s an example of a simple expression evaluator written using Parcon:

```from parcon import *
from decimal import Decimal
import operator
expr = Forward()
number = (+Digit() + -(SignificantLiteral(".") + +Digit()))[flatten]["".join][Decimal]
term = number | "(" + expr + ")"
term = InfixExpr(term, [("*", operator.mul), ("/", operator.truediv)])
term = InfixExpr(term, [("+", operator.add), ("-", operator.sub)])
expr << term
```

This expression evaluator can be used thus:

```print expr.parse_string("1+2") # prints 3
print expr.parse_string("1+2+3") # prints 6
print expr.parse_string("1+2+3+4") # prints 10
print expr.parse_string("3*4") # prints 12
print expr.parse_string("5+3*4") # prints 17
print expr.parse_string("(5+3)*4") # prints 32
print expr.parse_string("10/4") # prints 2.5
```

Parcon is currently much more comprehensively documented than Pargen is. Improved documentation for Pargen will come soon.