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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.
If your whitespace-significant grammar supports comments, then ``NL_type``
must match those comments too. Otherwise, comments that appear in the middle
of a line will `confuse Lark`_.
.. _`confuse Lark`: https://github.com/lark-parser/lark/issues/863
"""
from lark import Lark
from lark.indenter import Indenter
tree_grammar = r"""
%import common.CNAME -> NAME
%import common.WS_INLINE
%import common.SH_COMMENT
%ignore WS_INLINE
%ignore SH_COMMENT
%declare _INDENT _DEDENT
?start: _NL* tree
tree: NAME _NL [_INDENT tree+ _DEDENT]
_NL: (/\r?\n[\t ]*/ | SH_COMMENT)+
"""
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
# check this comment out
b
c
d
e
f
g
"""
def test():
print(parser.parse(test_tree).pretty())
if __name__ == '__main__':
test()
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