tatsu_calculator_grammar_parsing_expression_to_ast.py

1import json
2import tatsu
3
4GRAMMAR = '''
5    @@grammar::CALC
6
7    start = expression $ ;
8
9    expression
10        =
11        | left:expression op:'+' right:term
12        | left:expression op: '-' right:term
13        | term
14        ;
15
16    term
17        =
18        | left:term op:'*' right:factor
19        | left:term op:'/' right:factor
20        | factor
21        ;
22
23    factor
24        =
25        | '(' ~  @:expression ')'
26        | number
27        ;
28
29    number = /\d+/ ;
30'''
31
32def main():
33    parser = tatsu.compile(GRAMMAR)
34    ast = parser.parse('3 + 5 * ( 10 - 20 )')
35    print(json.dumps(ast, indent=2))
36
37if __name__ == '__main__':
38    main()