primitive- Primitive memory-related operations

Copyright(c) Roman Leshchinskiy 2009-2012
MaintainerRoman Leshchinskiy <>
Safe HaskellNone




Reexports all primitive operations



Naming Conventions

For historical reasons, this library embraces the practice of suffixing the name of a function with the type it operates on. For example, three of the variants of the array indexing function are:

indexArray      ::           Array      a -> Int -> a
indexSmallArray ::           SmallArray a -> Int -> a
indexPrimArray  :: Prim a => PrimArray  a -> Int -> a

In a few places, where the language sounds more natural, the array type is instead used as a prefix. For example, Data.Primitive.SmallArray exports smallArrayFromList, which would sound unnatural if it used SmallArray as a suffix instead.

This library provides several functions traversing, building, and filtering arrays. These functions are suffixed with an additional character to indicate their the nature of their effectfulness:

  • No suffix: A non-effectful pass over the array.
  • -A suffix: An effectful pass over the array, where the effect is Applicative.
  • -P suffix: An effectful pass over the array, where the effect is PrimMonad.

Additionally, an apostrophe can be used to indicate strictness in the elements. The variants with an apostrophe are used in Data.Primitive.Array but not in Data.Primitive.PrimArray since the array type it provides is always strict in the element. For example, there are three variants of the function that filters elements from a primitive array.

filterPrimArray  :: (Prim a               ) => (a ->   Bool) -> PrimArray a ->    PrimArray a
filterPrimArrayA :: (Prim a, Applicative f) => (a -> f Bool) -> PrimArray a -> f (PrimArray a)
filterPrimArrayP :: (Prim a, PrimMonad   m) => (a -> m Bool) -> PrimArray a -> m (PrimArray a)

As long as the effectful context is a monad that is sufficiently affine the behaviors of the Applicative and PrimMonad variants produce the same results and differ only in their strictness. Monads that are sufficiently affine include:

  • IO and ST
  • Any combination of MaybeT, ExceptT, StateT and Writer on top of another sufficiently affine monad.
  • Any Monad which does not include backtracking or other mechanism where an effect can happen more than once is an Affine Monad in the sense we care about. ContT, LogicT, ListT are all examples of search/control monads which are NOT affine: they can run a sub computation more than once.

There is one situation where the names deviate from effectful suffix convention described above. Throughout the haskell ecosystem, the Applicative variant of map is known as traverse, not mapA. Consequently, we adopt the following naming convention for mapping:

mapPrimArray :: (Prim a, Prim b) => (a -> b) -> PrimArray a -> PrimArray b
traversePrimArray :: (Applicative f, Prim a, Prim b) => (a -> f b) -> PrimArray a -> f (PrimArray b)
traversePrimArrayP :: (PrimMonad m, Prim a, Prim b) => (a -> m b) -> PrimArray a -> m (PrimArray b)