BSD-3-Clause licensed by Alexey Kuleshevich
Maintained by

Module documentation for

This version can be pinned in stack with:pvar-,1798


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


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pvar Hackage Nightly Nightly


Main features include:

  • Perfomance. 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 availiable in ghc-prim out of the box:
atomicModifyIntPVar :: PrimMonad m => PVar m Int -> (Int -> (Int, a)) -> m a
  • Works in PrimMonad, therfore 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.


Changelog for pvar

  • 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.

  • Initial release