Generates Toy language sentences

toylang.py

import random

class Rule:
    def __init__(self, name):
        self.name = name


GRAMMAR = {
    'op': ['+', '-', '/', '%', '*'],
    'var': ['x', 'y', 'z', '1', '2', '3'],
    'expr': [
        Rule('var'),
        (Rule('var'), Rule('op'), Rule('expr')),
        ('(', Rule('expr'), ')')
    ]
}

def generate(rule):
    if type(rule) is str:
        yield rule
        return

    if type(rule) is Rule:
        rules = GRAMMAR[rule.name]
        sample = rules[random.randint(0, len(rules)-1)]
        yield from generate(sample)
        return

    for x in rule:
        yield from generate(x)


if __name__ == '__main__':

    for _ in range(10000):
        print( ' '.join(generate(Rule('expr'))))