Data.Primitive

primitive-0.7.4.0: Primitive memory-related operations

Copyright | (c) Roman Leshchinskiy 2009-2012
License | BSD-style
Maintainer | Roman Leshchinskiy <rl@cse.unsw.edu.au>
Portability | non-portable
Safe Haskell | Safe-Inferred
Language | Haskell2010

Data.Primitive

Contents

- Re-exports
- Naming Conventions

Description

Reexports all primitive operations.

Synopsis

- module Data.Primitive.Types
- module Data.Primitive.Array
- module Data.Primitive.ByteArray
- module Data.Primitive.SmallArray
- module Data.Primitive.PrimArray
- module Data.Primitive.MutVar

# Re-exports

module Data.Primitive.Types

module Data.Primitive.Array

module Data.Primitive.ByteArray

module Data.Primitive.SmallArray

module Data.Primitive.PrimArray

module Data.Primitive.MutVar

# 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 for traversing, building, and filtering arrays. These functions are suffixed with an additional character to indicate 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 anyway.

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 mechanisms 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)