monad 0.1

什么？

python中的monad，以及一些有用的函数。

怎么做？

>>> from monad.decorators import maybe
>>> parse_int = maybe(int)
>>> parse_int(42)
Just(42)
>>> parse_int('42')
Just(42)
>>> parse_int('42.2')
Nothing

>>> parse_float = maybe(float)
>>> parse_float('42.2')
Just(42.2)

>>> from monad.actions import tryout
>>> parse_number = tryout(parse_int, parse_float)
>>> tokens = [2, '0', '4', 'eight', '10.0']
>>> [parse_number(token) for token in tokens]
[Just(2), Just(0), Just(4), Nothing, Just(10.0)]

>>> @maybe
... def reciprocal(n):
...     return 1. / n
>>> reciprocal(2)
Just(0.5)
>>> reciprocal(0)
Nothing

>>> process = parse_number >> reciprocal
>>> process('4')
Just(0.25)
>>> process('0')
Nothing
>>> [process(token) for token in tokens]
[Just(0.5), Nothing, Just(0.25), Nothing, Just(0.1)]
>>> [parse_number(token) >> reciprocal for token in tokens]
[Just(0.5), Nothing, Just(0.25), Nothing, Just(0.1)]
>>> [parse_number(token) >> reciprocal >> reciprocal for token in tokens]
[Just(2.0), Nothing, Just(4.0), Nothing, Just(10.0)]

为什么？

为什么不呢。