Data.Primitive.Types

Class of types supporting primitive array operations. This includes interfacing with GC-managed memory (functions suffixed with ByteArray#) and interfacing with unmanaged memory (functions suffixed with Addr#). Endianness is platform-dependent.

The size of values of type a in bytes. The argument is not used.

It is recommended to use sizeOfType instead.

This function has existed since 0.1, but was moved from Data.Primitive to Data.Primitive.Types in version 0.6.3.0.

The size of values of type a in bytes. This has to be used with TypeApplications: sizeOfType @a.

>>> :set -XTypeApplications>>> import Data.Int (Int32)>>> sizeOfType @Int324

The alignment of values of type a in bytes. The argument is not used.

It is recommended to use alignmentOfType instead.

This function has existed since 0.1, but was moved from Data.Primitive to Data.Primitive.Types in version 0.6.3.0.

The alignment of values of type a in bytes. This has to be used with TypeApplications: alignmentOfType @a.

An implementation of setByteArray# that calls writeByteArray# to set each element. This is helpful when writing a Prim instance for a multi-word data type for which there is no CPU-accelerated way to broadcast a value to contiguous memory. It is typically used alongside defaultSetOffAddr#. For example:

data Trip = Trip Int Int Int

instance Prim Trip
  sizeOfType# _ = 3# *# sizeOfType# (proxy# :: Proxy# Int)
  alignmentOfType# _ = alignmentOfType# (proxy# :: Proxy# Int)
  indexByteArray# arr# i# = ...
  readByteArray# arr# i# = ...
  writeByteArray# arr# i# (Trip a b c) =
    \s0 -> case writeByteArray# arr# (3# *# i#) a s0 of
       s1 -> case writeByteArray# arr# ((3# *# i#) +# 1#) b s1 of
         s2 -> case writeByteArray# arr# ((3# *# i#) +# 2# ) c s2 of
           s3 -> s3
  setByteArray# = defaultSetByteArray#
  indexOffAddr# addr# i# = ...
  readOffAddr# addr# i# = ...
  writeOffAddr# addr# i# (Trip a b c) =
    \s0 -> case writeOffAddr# addr# (3# *# i#) a s0 of
       s1 -> case writeOffAddr# addr# ((3# *# i#) +# 1#) b s1 of
         s2 -> case writeOffAddr# addr# ((3# *# i#) +# 2# ) c s2 of
           s3 -> s3
  setOffAddr# = defaultSetOffAddr#

An implementation of setOffAddr# that calls writeOffAddr# to set each element. The documentation of defaultSetByteArray# provides an example of how to use this.

Newtype that uses a Prim instance to give rise to a Storable instance. This type is intended to be used with the DerivingVia extension available in GHC 8.6 and up. For example, consider a user-defined Prim instance for a multi-word data type.

data Uuid = Uuid Word64 Word64
  deriving Storable via (PrimStorable Uuid)
instance Prim Uuid where ...

Writing the Prim instance is tedious and unavoidable, but the Storable instance comes for free once the Prim instance is written.

A value of type Ptr a represents a pointer to an object, or an array of objects, which may be marshalled to or from Haskell values of type a.

The type a will often be an instance of class Storable which provides the marshalling operations. However this is not essential, and you can provide your own operations to access the pointer. For example you might write small foreign functions to get or set the fields of a C struct.