| """ | |
| Parsing Indentation | |
| =================== | |
| A demonstration of parsing indentation (“whitespace significant” language) | |
| and the usage of the Indenter class. | |
| Since indentation is context-sensitive, a postlex stage is introduced to | |
| manufacture INDENT/DEDENT tokens. | |
| It is crucial for the indenter that the NL_type matches | |
| the spaces (and tabs) after the newline. | |
| """ | |
| from lark import Lark | |
| from lark.indenter import Indenter | |
| tree_grammar = r""" | |
| ?start: _NL* tree | |
| tree: NAME _NL [_INDENT tree+ _DEDENT] | |
| %import common.CNAME -> NAME | |
| %import common.WS_INLINE | |
| %declare _INDENT _DEDENT | |
| %ignore WS_INLINE | |
| _NL: /(\r?\n[\t ]*)+/ | |
| """ | |
| class TreeIndenter(Indenter): | |
| NL_type = '_NL' | |
| OPEN_PAREN_types = [] | |
| CLOSE_PAREN_types = [] | |
| INDENT_type = '_INDENT' | |
| DEDENT_type = '_DEDENT' | |
| tab_len = 8 | |
| parser = Lark(tree_grammar, parser='lalr', postlex=TreeIndenter()) | |
| test_tree = """ | |
| a | |
| b | |
| c | |
| d | |
| e | |
| f | |
| g | |
| """ | |
| def test(): | |
| print(parser.parse(test_tree).pretty()) | |
| if __name__ == '__main__': | |
| test() | |