>>> import d20
>>> result = d20.roll("1d20+5")
>>> str(result)
'1d20 (10) + 5 = `15`'
>>> result.total
15
>>> result.crit
<CritType.NORMAL: 0>
>>> str(result.ast)
'1d20 + 5'

>>> from d20 import roll
>>> r = roll("4d6kh3")  # highest 3 of 4 6-sided dice
>>> r.total
14
>>> str(r)
'4d6kh3 (4, 4, **6**, ~~3~~) = `14`'

>>> r = roll("2d6ro<3")  # roll 2d6s, then reroll any 1s or 2s once
>>> r.total
9
>>> str(r)
'2d6ro<3 (**~~1~~**, 3, **6**) = `9`'

>>> r = roll("8d6mi2")  # roll 8d6s, with each die having a minimum roll of 2
>>> r.total
33
>>> str(r)
'8d6mi2 (1 -> 2, **6**, 4, 2, **6**, 2, 5, **6**) = `33`'

>>> r = roll("(1d4 + 1, 3, 2d6kl1)kh1")  # the highest of 1d4+1, 3, and the lower of 2 d6s
>>> r.total
3
>>> str(r)
'(1d4 (2) + 1, ~~3~~, ~~2d6kl1 (2, 5)~~)kh1 = `3`'

>>> import d20
>>> class MyStringifier(d20.SimpleStringifier):
...     def _stringify(self, node):
...         if not node.kept:
...             return 'X'
...         return super()._stringify(node)
...
...     def _str_expression(self, node):
...         return f"The result of the roll {self._stringify(node.roll)} was {int(node.total)}"

>>> result = d20.roll("4d6e6kh3", stringifier=MyStringifier())
>>> str(result)
'The result of the roll 4d6e6kh3 (X, 5, 6!, 6!, X, X) was 17'

>>> from d20 import roll
>>> str(roll("3d6 [fire] + 1d4 [piercing]"))
'3d6 (3, 2, 2) [fire] + 1d4 (3) [piercing] = `10`'

>>> str(roll("-(1d8 + 3) [healing]"))
'-(1d8 (7) + 3) [healing] = `-10`'

>>> str(roll("(1 [one], 2 [two], 3 [three])"))
'(1 [one], 2 [two], 3 [three]) = `6`'

>>> from d20 import roll
>>> result = roll("1d20 I rolled a d20", allow_comments=True)
>>> str(result)
'1d20 (13) = `13`'
>>> result.comment
'I rolled a d20'

>>> from d20 import roll
>>> result = roll("3d6 + 1d4 + 3")
>>> str(result)
'3d6 (4, **6**, **6**) + 1d4 (**1**) + 3 = `20`'
>>> result.expr
<Expression roll=<BinOp left=<BinOp left=<Dice num=3 size=6 values=[<Die size=6 values=[<Literal 4>]>, <Die size=6 values=[<Literal 6>]>, <Die size=6 values=[<Literal 6>]>] operations=[]> op=+ right=<Dice num=1 size=4 values=[<Die size=4 values=[<Literal 1>]>] operations=[]>> op=+ right=<Literal 3>> comment=None>

>>> from d20 import roll

>>> binop = roll("1 + 2 + 3 + 4")
>>> left = binop.expr
>>> while left.children:
...     left = left.children[0]
>>> left
<Literal 1>

>>> right = binop.expr
>>> while right.children:
...     right = right.children[-1]
>>> right
<Literal 4>

>>> from d20 import utils  # these patterns are available in the utils submodule:
>>> utils.leftmost(binop.expr)
<Literal 1>
>>> utils.rightmost(binop.expr)
<Literal 4>

>>> from d20 import roll, Dice, SimpleStringifier, utils

>>> mixed = roll("-1d8 + 4 - (3, 1d4)kh1")
>>> str(mixed)
'-1d8 (**8**) + 4 - (3, ~~1d4 (3)~~)kh1 = `-7`'
>>> root = mixed.expr
>>> result = utils.dfs(root, lambda node: isinstance(node, Dice) and node.num == 1 and node.size == 4)
>>> result
<Dice num=1 size=4 values=[<Die size=4 values=[<Literal 3>]>] operations=[]>
>>> SimpleStringifier().stringify(result)
'1d4 (3)'