parser.py

import parsec as p

whitespace = p.regex(r'\s+')
ignore = p.many(whitespace)
lexeme = lambda parser: parser.skip(ignore)
lparen = lexeme(p.string('('))
rparen = lexeme(p.string(')'))
symbol = lexeme(p.regex(r'[\d\w_-]+'))
and_op = lexeme(p.string('and'))
or_op = lexeme(p.string('or'))
op = and_op | or_op
atom = op | symbol


@p.generate('binary expression')
def binary_expr():
    yield lparen
    es = yield p.many(expr)
    yield rparen
    return es


expr = atom | binary_expr
program = p.many(expr).skip(ignore)


def parse_gpr(string):
    """Parse a gene boolean expression."""
    return program(string, 0)