Copyright	(c) Michael Szvetits 2021
License	BSD3 (see the file LICENSE)
Maintainer	typedbyte@qualified.name
Stability	stable
Portability	portable
Safe Haskell	Safe-Inferred
Language	Haskell2010

Control.Program

Contents

Program Representation
Resource Handling
Environment Handling

Description

Types and functions for representing programs which run in a specific environment and are able to integrate bracket-like operations.

Synopsis

data Program e a
runProgram :: e -> Program e a -> IO a
bracket :: IO a -> (a -> IO b) -> Program e a
bracketE :: (e -> IO a) -> (e -> a -> IO b) -> Program e a
manage :: (forall b. (a -> IO b) -> IO b) -> Program e a
local :: Program e a -> Program e a
class Has e t where
- from :: e -> t
ask :: Program e e
pull :: e `Has` t => Program e t
pullWith :: e `Has` t => (t -> IO a) -> Program e a

Program Representation

data Program e a Source #

Represents a program that produces a value of type a when running in an environment e. The required content of the environment is usually described by declaring Has constraints on e.

Turning an IO action into a Program is usually done by using liftIO.

Instances

Instances details

Monad (Program e) Source #
Instance details Defined in Control.Program Methods (>>=) :: Program e a -> (a -> Program e b) -> Program e b # (>>) :: Program e a -> Program e b -> Program e b # return :: a -> Program e a #
Functor (Program e) Source #
Instance details Defined in Control.Program Methods fmap :: (a -> b) -> Program e a -> Program e b # (<$) :: a -> Program e b -> Program e a #
MonadFail (Program e) Source #
Instance details Defined in Control.Program Methods fail :: String -> Program e a #
Applicative (Program e) Source #
Instance details Defined in Control.Program Methods pure :: a -> Program e a # (<>) :: Program e (a -> b) -> Program e a -> Program e b # liftA2 :: (a -> b -> c) -> Program e a -> Program e b -> Program e c # (>) :: Program e a -> Program e b -> Program e b # (<*) :: Program e a -> Program e b -> Program e a #
MonadIO (Program e) Source #
Instance details Defined in Control.Program Methods liftIO :: IO a -> Program e a #

runProgram :: e -> Program e a -> IO a Source #

Runs a program in a given environment e.

Resource Handling

bracket Source #

Arguments

:: IO a	The computation which acquires the resource.
-> (a -> IO b)	The computation which releases the resource.
-> Program e a	The computation which uses the resource.

Acquire a resource, use it, and then release the resource automatically after the program ends.

bracketE :: (e -> IO a) -> (e -> a -> IO b) -> Program e a Source #

A version of bracket where the acquisition and release actions may consult the environment e.

manage :: (forall b. (a -> IO b) -> IO b) -> Program e a Source #

Integrates a continuation into a Program, which is useful for integrating existing bracket-like continuations (often named with...).

local :: Program e a -> Program e a Source #

Runs a sub-program within a program, which is useful for fine-grained resource handling (i.e., resources acquired by the sub-program are released after the sub-program ends, not at the end of the whole program).

Environment Handling

class Has e t where Source #

Demands that a specific value of type t must be present in the environment e.

Methods

from :: e -> t Source #

Extracts a value of type t from the environment e.

Instances

Instances details

Has e e Source #
Instance details Defined in Control.Program Methods from :: e -> e Source #

ask :: Program e e Source #

Gets the environment.

pull :: e `Has` t => Program e t Source #

Extracts a specific value of type t from the environment.

pullWith :: e `Has` t => (t -> IO a) -> Program e a Source #

Extracts a specific value of type t from the environment and extracts some IO action from it. This is useful if the environment contains a record of IO functions (e.g., a function which returns a handle).