Portability  nonportable (type families) 

Stability  experimental 
Maintainer  ross@soi.city.ac.uk 
Safe Haskell  SafeInferred 
 Computation type:
 Computations which read values from a shared environment.
 Binding strategy:
 Monad values are functions from the environment to a value. The bound function is applied to the bound value, and both have access to the shared environment.
 Useful for:
 Maintaining variable bindings, or other shared environment.
 Zero and plus:
 None.
 Example type:

Reader
[(String,Value)] a
The Reader
monad (also called the Environment monad).
Represents a computation, which can read values from
a shared environment, pass values from function to function,
and execute subcomputations in a modified environment.
Using Reader
monad for such computations is often clearer and easier
than using the State
monad.
Inspired by the paper /Functional Programming with Overloading and HigherOrder Polymorphism/, Mark P Jones (http://web.cecs.pdx.edu/~mpj/) Advanced School of Functional Programming, 1995.
Documentation
class Monad m => MonadReader m whereSource
See examples in Control.Monad.Reader.
Note, the partially applied function type (>) r
is a simple reader monad.
See the instance
declaration below.
Retrieves the monad environment.
:: (EnvType m > EnvType m)  The function to modify the environment. 
> m a 

> m a 
Executes a computation in a modified environment.
MonadReader ((>) r)  
MonadReader m => MonadReader (MaybeT m)  
MonadReader m => MonadReader (ListT m)  
MonadReader m => MonadReader (IdentityT m)  
(Monoid w, MonadReader m) => MonadReader (WriterT w m)  
(Monoid w, MonadReader m) => MonadReader (WriterT w m)  
MonadReader m => MonadReader (StateT s m)  
MonadReader m => MonadReader (StateT s m)  
Monad m => MonadReader (ReaderT r m)  
(Error e, MonadReader m) => MonadReader (ErrorT e m)  
MonadReader m => MonadReader (ContT r m)  
(Monoid w, Monad m) => MonadReader (RWST r w s m)  
(Monoid w, Monad m) => MonadReader (RWST r w s m) 
:: MonadReader m  
=> (EnvType m > a)  The selector function to apply to the environment. 
> m a 
Retrieves a function of the current environment.