Tutorial 4 Subclassing Node

まんま

>>> from lepl import *
>>> class Add(Node): pass
...
>>> class Sub(Node): pass
...
>>> class Mul(Node): pass
...
>>> class Div(Node): pass
...
>>> symbol = Token('[^0-9a-zA-Z \t\r\n]')
>>> value = Token(UnsignedFloat())
>>> negfloat = lambda x: -float(x)
>>> number = Or(value >> float, ~symbol('-') & value >> negfloat)
>>> group2, group3 = Delayed(), Delayed()
>>> parens = ~symbol('(') & group3 & ~symbol(')')
>>> group1 = parens | number
>>> mul = group1 & ~symbol('*') & group2 > Mul
>>> div = group1 & ~symbol('/') & group2 > Div
>>> group2 += mul | div | group1
>>> add = group2 & ~symbol('+') & group3 > Add
>>> sub = group2 & ~symbol('-') & group3 > Sub
>>> group3 += add | sub | group2
>>> ast = group3.parse('1+2*(3-4)+5/6+7')[0]
>>> print(ast)
Add
 +- 1.0
 `- Add
     +- Mul
     |   +- 2.0
     |   `- Sub
     |       +- 3.0
     |       `- 4.0
     `- Add
         +- Div
         |   +- 5.0
         |   `- 6.0
         `- 7.0