pymonad

Some monadic value holders for Python

Install

Install from the github repository:

with pipenv:

# should be installed in editable mode to ensure an up-to-date copy of the repository and that it includes all known dependencies -> '-e'
pipenv install -e git+https://github.com/lucsorel/pymonad.git#egg=pymonad

with pip:

pip3 install git+https://github.com/lucsorel/pymonad.git

Usages

Val (= Union[Some, Nothing])

A classic Maybe or Optional monad, with a shorter name and some extra functions (other people discuss wether Optional is really a monad or not).

nullableText = 'lullaby'

# None-safe value mapper
upperedText = Val.of(nullableText).map(
    # mapper called only on non-null values
    lambda text: text.upper()
).get() # returns None if the initial value was None, or if the mapper produces a None value

# None-safe value flat-mapper
upperedText = Val.of(nullableText).flatMap(
    # mapper called only on non-null values
    lambda text: Val.of(text.lower())
).get() # returns None if the initial value was None, or if the mapper produces a None value

# default value
Val.of(nullableText).map(
    lambda text: text.upper()
).get('OPTIONAL_DEFAULT_VALUE') # optional default value


# default value in an alternate producer (wraps creation costs)
upperedText = Val.of(nullableText).map(
    lambda text: text.upper()
).orElseCall(lambda: 'ALTERNATE') # called only if necessary

upperedText = Val.of(nullableText).map(
    lambda text: text.upper()
).orElseFlatCall(lambda: Val.of('ALTERNATE')) # called only if necessary


# handles multiple vals
givennameVal = Val.of('Frankie')
lastnameVal = Val.of('Manning')
loweredFullname = Val.flatMapAllOrElse(
    [givennameVal, lastnameVal],
    # called if ALL vals have values
    lambda text1, text2: Val.of(f'{givennameVal} {lastnameVal}'),
    # alternate producer called if at least one val has a None value
    lambda: Val.of('either no text1 nor text2')
).map(
    lambda text: text.lower()
).get()

Licence

Unless stated otherwise all works are licensed under the MIT license, a copy of which is included here.

Contributions

Luc Sorel-Giffo

Pull-requests are welcome and will be processed on a best-effort basis.