mtl-2.2.1: Monad classes, using functional dependencies

Copyright(c) Andy Gill 2001, (c) Oregon Graduate Institute of Science and Technology 2001, (c) Jeff Newbern 2003-2006, (c) Andriy Palamarchuk 2006
LicenseBSD-style (see the file LICENSE)
Maintainerlibraries@haskell.org
Stabilityexperimental
Portabilityportable
Safe HaskellSafe-Inferred
LanguageHaskell98

Control.Monad.Identity

Description

Computation type:
Simple function application.
Binding strategy:
The bound function is applied to the input value. Identity x >>= f == Identity (f x)
Useful for:
Monads can be derived from monad transformers applied to the Identity monad.
Zero and plus:
None.
Example type:
Identity a

The 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 Identity monad 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.

Documentation