testbed/lark-parser__lark/examples/advanced/_json_parser.py

"""
Simple JSON Parser
==================

The code is short and clear, and outperforms every other parser (that's written in Python).
For an explanation, check out the JSON parser tutorial at /docs/json_tutorial.md

(this is here for use by the other examples)
"""
import sys

from lark import Lark, Transformer, v_args

json_grammar = r"""
    ?start: value

    ?value: object
          | array
          | string
          | SIGNED_NUMBER      -> number
          | "true"             -> true
          | "false"            -> false
          | "null"             -> null

    array  : "[" [value ("," value)*] "]"
    object : "{" [pair ("," pair)*] "}"
    pair   : string ":" value

    string : ESCAPED_STRING

    %import common.ESCAPED_STRING
    %import common.SIGNED_NUMBER
    %import common.WS

    %ignore WS
"""


class TreeToJson(Transformer):
    @v_args(inline=True)
    def string(self, s):
        return s[1:-1].replace('\\"', '"')

    array = list
    pair = tuple
    object = dict
    number = v_args(inline=True)(float)

    null = lambda self, _: None
    true = lambda self, _: True
    false = lambda self, _: False


### Create the JSON parser with Lark, using the LALR algorithm
json_parser = Lark(json_grammar, parser='lalr',
                   # Using the standard lexer isn't required, and isn't usually recommended.
                   # But, it's good enough for JSON, and it's slightly faster.
                   lexer='standard',
                   # Disabling propagate_positions and placeholders slightly improves speed
                   propagate_positions=False,
                   maybe_placeholders=False,
                   # Using an internal transformer is faster and more memory efficient
                   transformer=TreeToJson())