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

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.