Pypargen

Pypargen is a Parser generator in python. It creates parsers for LR(1) grammars. Currently pypargen cannot create parser for LR(k > 1). You can write grammar in a simple format (which I call grm format).

Example: Math expressions

The grammar for math expressions is:

atom -> "[1-9][0-9]*"
atom -> "(" sub ")"
div  -> div "/" atom
div  -> atom
mul  -> mul "*" div
mul  -> div
add  -> add "+" mul
add  -> mul
sub  -> sub "-" add
sub  -> add
expr -> sub "\n\n*"

For every rule, you need to provide a callback that will take the same number of arguments as right side of every rule and returns the object that represents the left side of the rule.

For example for add -> add "+" mul rule, the callback could be:

def add(a, _plus, b):
	return a + b

import pypargen as pgen

# Parse the grm file first
gparser = pgen.GrmParser()
with open("math.grm") as fp:
	math_grammar = parser.parse(fp)

# See examples/math.py for example of callbacks.
parser = pgen.Parser(math_grammar, callbacks)
result = parser.parse(sys.stdin)
print(result)