reader package:transformers

Constructor for computations in the reader monad (equivalent to asks).

Constructor for computations in the reader monad (equivalent to asks).

Constructor for computations in the reader monad (equivalent to asks).

Declaration of the ReaderT monad transformer, which adds a static environment to a given monad. If the computation is to modify the stored information, use Control.Monad.Trans.State instead.

The parameterizable reader monad, which is non-strict. Computations are functions of a shared environment. The return function ignores the environment, while m >>= k passes the inherited environment to both subcomputations:

Convert a read-only computation into an accumulation computation.

The reader monad transformer, which adds a read-only environment to the given monad. The return function ignores the environment, while m >>= k passes the inherited environment to both subcomputations: ReaderT r m is strict if and only if m is.

Transform the value returned by a Reader.

• runReader (mapReader f m) = f .
  runReader m

Transform the computation inside a ReaderT.

• runReaderT (mapReaderT f m) = f .
  runReaderT m

Runs a Reader and extracts the final value from it. (The inverse of reader.)

Execute a computation in a modified environment (a specialization of withReaderT).

• runReader (withReader f m) = runReader m
  . f

Execute a computation in a modified environment (a more general version of local).

• runReaderT (withReaderT f m) =
  runReaderT m . f