Control.Program.State

Types and functions for handling mutable state in the environment of a Program.

State Effect

data State s

A record of functions which represents the operations on a mutable value.

Constructors

State

Fields

• readState :: IO s

  Gets the current state.

• writeState :: s -> IO ()

  Replaces the state with a new value.

Program-based State

get :: e `Has` State s => Program e s

Gets the current state.

put :: e `Has` State s => s -> Program e ()

Replaces the state with a new value.

modify :: e `Has` State s => (s -> s) -> Program e ()

Modifies the state, using the provided function.

modify' :: e `Has` State s => (s -> s) -> Program e ()

A strict version of modify.

IO-based State

newState :: s -> IO (State s)

Creates a new record of functions for mutable state, backed by an IORef.

modifyState :: State s -> (s -> s) -> IO ()

Modifies the state, using the provided function.

modifyState' :: State s -> (s -> s) -> IO ()

A strict version of modifyState.