Copyright | (c) Andy Gill 2001 (c) Oregon Graduate Institute of Science and Technology 2001 (c) Jeff Newbern 2003-2007 (c) Andriy Palamarchuk 2007 |
---|---|
License | BSD-style (see the file LICENSE) |
Maintainer | [email protected] |
Stability | experimental |
Portability | non-portable (multi-param classes, functional dependencies) |
Safe Haskell | Safe |
Language | Haskell2010 |
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 sub-computations 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 Higher-Order Polymorphism, Mark P Jones (http://web.cecs.pdx.edu/~mpj/) Advanced School of Functional Programming, 1995.
class Monad m => MonadReader r m | m -> r where Source
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.
:: (r -> r) | The function to modify the environment. |
-> m a |
|
-> m a |
Executes a computation in a modified environment.
:: (r -> a) | The selector function to apply to the environment. |
-> m a |
Retrieves a function of the current environment.
MonadReader r m => MonadReader r (MaybeT m) | |
MonadReader r m => MonadReader r (ListT m) | |
(Monoid w, MonadReader r m) => MonadReader r (WriterT w m) | |
(Monoid w, MonadReader r m) => MonadReader r (WriterT w m) | |
MonadReader r m => MonadReader r (StateT s m) | |
MonadReader r m => MonadReader r (StateT s m) | |
MonadReader r m => MonadReader r (IdentityT m) | |
MonadReader r m => MonadReader r (ExceptT e m) | Since: mtl-2.2 |
(Error e, MonadReader r m) => MonadReader r (ErrorT e m) | |
Monad m => MonadReader r (ReaderT r m) | |
MonadReader r' m => MonadReader r' (ContT r m) | |
MonadReader r ((->) r :: Type -> Type) | |
(Monad m, Monoid w) => MonadReader r (RWST r w s m) | |
(Monad m, Monoid w) => MonadReader r (RWST r w s m) | |
:: MonadReader r m | |
=> (r -> a) | The selector function to apply to the environment. |
-> m a |
Retrieves a function of the current environment.
© The University of Glasgow and others
Licensed under a BSD-style license (see top of the page).
https://downloads.haskell.org/~ghc/8.8.3/docs/html/libraries/mtl-2.2.2/Control-Monad-Reader-Class.html