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"""
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()
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