reader

Retrieves a function of the current environment.

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).

Read some text. If the read succeeds, return its value and the remaining text, otherwise an error message.

• 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 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.

The parameterizable reader monad. Computations are functions of a shared environment. The return function ignores the environment, while >>= passes the inherited environment to both subcomputations.

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:

GHC uses several kinds of name internally:

• OccName: see GHC.Types.Name.Occurrence#name_types
• RdrName is the type of names that come directly from the parser. They have not yet had their scoping and binding resolved by the renamer and can be thought of to a first approximation as an OccName with an optional module qualifier
• Name: see GHC.Types.Name#name_types
• Id: see GHC.Types.Id#name_types
• Var: see GHC.Types.Var#name_types

Convert a read-only computation into an accumulation computation.

Not on Stackage, so not searched. Vinyl-based reader-like monad composition

The reader monad transformer, which adds a read-only environment to the given monad. The return function ignores the environment, while >>= passes the inherited environment to both subcomputations.

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.

A ReaderTable describes how to deserialise a table from disk, and how to create a BinaryReader that looks up values in the deduplication table.

UserData required to deserialise symbols for interface files. See Note [Binary UserData]

See examples in Control.Monad.Reader. Note, the partially applied function type (->) r is a simple reader monad. See the instance declaration below.

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.)