Manual：Operators：Operators That Apply Functions To Results：**

>>> from lepl import *
>>> def show(stream_in, stream_out, results):
...     print('stream_in:', stream_in)
...     print('stream_out:', stream_out)
...     print('results:', results)
...
>>> (Literal('a') ** show).parse('abc')
stream_in: abc
stream_out: bc
results: ['a']
[None]
>>> KApply(Literal('a'), show).parse('abc')
stream_in: abc
stream_out: bc
results: ['a']
[None]