| Safe Haskell | None |
|---|---|
| Language | Haskell2010 |
Context
Contents
Synopsis
- data Store ctx
- withNonEmptyStore :: ctx -> (Store ctx -> IO a) -> IO a
- withEmptyStore :: (Store ctx -> IO a) -> IO a
- use :: Store ctx -> ctx -> IO a -> IO a
- adjust :: Store ctx -> (ctx -> ctx) -> IO a -> IO a
- mine :: Store ctx -> IO ctx
- mines :: Store ctx -> (ctx -> a) -> IO a
- mineMay :: Store ctx -> IO (Maybe ctx)
- minesMay :: Store ctx -> (ctx -> a) -> IO (Maybe a)
- module Context.View
- data NotFoundException = NotFoundException {}
- module Context.Concurrent
- module Context.Storage
Introduction
This module provides an opaque Store for thread-indexed storage around
arbitrary context values. The interface supports nesting context values per
thread, and at any point, the calling thread may ask for its current context.
Note that threads in Haskell have no explicit parent-child relationship. So if
you register a context in a Store produced by withEmptyStore, spin up a
separate thread, and from that thread you ask for a context, that thread will
not have a context in the Store. Use Context.Concurrent as a drop-in
replacement for Control.Concurrent to have the library handle context
propagation from one thread to another automatically. Otherwise, you must
explicitly register contexts from each thread when using a Store produced by
withEmptyStore.
If you have a default context that is always applicable to all threads, you may
wish to use withNonEmptyStore. All threads may access this default context
(without leveraging Context.Concurrent or explicitly registering context
for the threads) when using a Store produced by withNonEmptyStore.
Regardless of how you initialize your Store, every thread is free to nest its
own specific context values.
This module is designed to be imported qualified:
import qualified Context
Storage
Opaque type that manages thread-indexed storage of context values.
Since: 0.1.0.0
Operations
Registering context
use :: Store ctx -> ctx -> IO a -> IO a Source #
Register a context in the specified Store on behalf of the calling
thread, for the duration of the specified action.
Since: 0.1.0.0
adjust :: Store ctx -> (ctx -> ctx) -> IO a -> IO a Source #
Adjust the calling thread's context in the specified Store for the
duration of the specified action. Throws a NotFoundException when the
calling thread has no registered context.
Since: 0.1.0.0
Asking for context
mine :: Store ctx -> IO ctx Source #
Provide the calling thread its current context from the specified
Store. Throws a NotFoundException when the calling thread has no
registered context.
Since: 0.1.0.0
mines :: Store ctx -> (ctx -> a) -> IO a Source #
Provide the calling thread a selection from its current context in the
specified Store. Throws a NotFoundException when the calling
thread has no registered context.
Since: 0.1.0.0
mineMay :: Store ctx -> IO (Maybe ctx) Source #
Provide the calling thread its current context from the specified
Store, if present.
Since: 0.1.0.0
minesMay :: Store ctx -> (ctx -> a) -> IO (Maybe a) Source #
Provide the calling thread a selection from its current context in the
specified Store, if present.
Since: 0.1.0.0
Views
module Context.View
Exceptions
data NotFoundException Source #
An exception which may be thrown when the calling thread does not have a registered context.
Since: 0.1.0.0
Constructors
| NotFoundException | |
Instances
Concurrency
module Context.Concurrent
Lower-level storage
module Context.Storage