Haskell Language Monads Definition of Monad
Example
class Monad m where
return :: a -> m a
(>>=) :: m a -> (a -> m b) -> m b
The most important function for dealing with monads is the bind operator >>=:
(>>=) :: m a -> (a -> m b) -> m b
- Think of
m aas "an action with anaresult". - Think of
a -> m bas “an action (depending on anaparameter) with abresult.”.
>>= sequences two actions together by piping the result from the first action to the second.
The other function defined by Monad is:
return :: a -> m a
Its name is unfortunate: this return has nothing to do with the return keyword found in imperative programming languages.
return x is the trivial action yielding x as its result. (It is trivial in the following sense:)
return x >>= f ≡ f x -- “left identity” monad law
x >>= return ≡ x -- “right identity” monad law
