monpy

Monad decorators mini-lib for python.

Bringing simple functional programming to python.

Example

In this example a do block is used to remove the need for nested if statements.

Maybe.do(
    x = lambda s: may_fail(...),
    y = lambda s: Maybe.wrap(wont_fail(s.x)),
    z = lambda s: may_also_fail(s.x, s.y)
).map(lambda s: s.z) # return z

For more examples see example.py.

Decorations

Each decorator in order expects that the previous one has been applied and that all the qualifications are met:

@functor:

• expects obj.map: Impliments functor map funcitonality.
• provides cls.mmap: Refactors a function to map through successive layers of a functor.

@applicative:

• expects cls.wrap: Trivially constructs a "singleton" instance.
• expects obj.apply: Combines a wrapped function to a wrapped value to produce a wrapped result.
• provides cls.lift: Refactors a function to map through successive layers of a functor.

@monad:

• expects obj.bind: Generalisation of flatmap.
• provides cls.do: Constructs a do block (like in Haskell) using an ordered dictionary of lambdas from state to wrapped value.
• provides cls.loop: Constructs a recursive do block using an ordered dictionary of lambdas from state to wrapped value that only runs whilst the predicate is true.

Types

The library comes with a handful of monad types:

• Box For simple wrapping.
• Maybe For optional values.
• Many For multiple values.
• Func For lambdas.
• Async For asyncronous lambdas.

Helpers

The library also includes some helper functions:

• curry Seperates positional arguments into seperate calls.
• un_curry Inverts curry.
• flatten Simplifies nested monads using type checking.

About "Do"

The Do type exists to represent the state of a procedure as a wrapped dictionaty with an overloaded __getattribute__ method to make do syntax clean.

.do will retrieve the dictionary itself.