pvar

Mutable variable with primitive values

BSD-3-Clause licensed by Alexey Kuleshevich

Maintained by [email protected]

This version can be pinned in stack with:pvar-1.0.0.0@sha256:3d4a6855b0960baee78f6956f082eb8aa1cede52d2955b7faef186d1133f7964,1893

Depends on 3 packages(full list with versions):

Used by 1 package in nightly-2024-11-08(full list with versions):

Interface for a mutable variable PVar that can hold values that have Prim instance.

Status

Language	Travis	Azure	Coveralls

Package	Hackage	Nightly	LTS
`pvar`

Main features include:

Performance. There is practically no overhead when compared to operating on pure values, although there is a higher memory overhead, since PVar is backed by a MutableByteArray#
Atomic operations for PVars with Int values. This includes a unique function that is not available in ghc-prim out of the box:

atomicModifyIntPVar :: PrimMonad m => PVar m Int -> (Int -> (Int, a)) -> m a

Works in PrimMonad, therefore it is usable with ST, IO and various transformer monads.
Easy access to PVar contents with Storable
isByteArrayPinned, isMutableByteArrayPinned function that work on ghc-7.10 and ghc-8.0 as well as all the newer ones.

Switch to MonadPrim type classes that was introduced in primitive-0.7.1.0
Fix definition PVar m a -> PVar a s. Parametrization on a monad is not general enough for some cases and making state token s last allows to use it with forall easier.
Relax monad in conversion to ForeignPtr

Rename modifyPVar to fetchModifyPVar and modifyPVarM to fetchModifyPVarM. This is a breaking change in favor of consistency with other librarries.
New implementation for modifyPVar and modifyPVarM that can return some artifact.
Addition of modifyFetchPVar and modifyFetchPVarM
Addition of atomicModifyFetchIntPVar and atomicFetchModifyIntPVar

Addition of backwards compatible:
- isByteArrayPinned, isMutableByteArrayPinned (that work on ghc-7.10 and ghc-8.0)
- Primitive versions isByteArrayPinned#, isMutableByteArrayPinned#
Support for GHC 7.10 and GHC 8.0
Re-export sizeOf and alignment for easier compatibility with older primitive versions.