The Monad Class

class hymn.types.monad.Monad(value)

Bases: object

the monad class

Implements bind operator >> and inverted bind operator << as syntactic sugar. It is equivalent to (>>=) and (=<<) in haskell, not to be confused with (>>) and (<<) in haskell.

As python treats assignments as statements, there is no way we can overload >>= as a chainable bind, be it directly overloaded through __irshift__, or derived by python itself through __rshift__.

The default implementations of bind(), fmap() and join() are mutual recursive, subclasses should at least either override bind(), or fmap() and join(), or all of them for better performance.

bind(f)

the bind operation

f is a function that maps from the underlying value to a monadic type, something like signature f :: a -> M a in haskell’s term.

The default implementation defines bind() in terms of fmap() and join().

fmap(f)

the fmap operation

The default implementation defines fmap() in terms of bind() and unit().

join()

the join operation

The default implementation defines join() in terms of bind() and identity function.

classmethod monadic(f)

decorator that turn f into monadic function of the monad

classmethod unit(value)

the unit of monad