- Computation type:
- Simple function application.
- Binding strategy:
- The bound function is applied to the input value.
Identityx >>= f ==
- Useful for:
- Monads can be derived from monad transformers applied to the
- Zero and plus:
- Example type:
Identity monad is a monad that does not embody any computational strategy.
It simply applies the bound function to its input without any modification.
Computationally, there is no reason to use the
instead of the much simpler act of simply applying functions to their arguments.
The purpose of the
Identity monad is its fundamental role in the theory
of monad transformers.
Any monad transformer applied to the
Identity monad yields a non-transformer
version of that monad.
Inspired by the paper /Functional Programming with Overloading and Higher-Order Polymorphism/, Mark P Jones (http://www.cse.ogi.edu/~mpj/) Advanced School of Functional Programming, 1995.
Identity wrapper. Abstraction for wrapping up a object. If you have an monadic function, say:
example :: Int -> Identity Int example x = return (x*x)
you can "run" it, using
Main> runIdentity (example 42) 1764 :: Int
A typical use of the Identity monad is to derive a monad from a monad transformer.
-- derive the
Control.Monad.State.Statemonad using the
Control.Monad.State.StateTmonad transformer type
Control.Monad.State.States a =
label is used in the type definition because it follows
a style of monad definition that explicitly represents monad values as
computations. In this style, a monadic computation is built up using the monadic
operators and then the value of the computation is extracted
Identity monad does not do any computation, its definition
For a better example of this style of monad,