primitive-0.3: Wrappers for primitive operations

MaintainerRoman Leshchinskiy <>



Primitive boxed arrays



data Array a Source

Boxed arrays


Array (Array# a) 


data MutableArray s a Source

Mutable boxed arrays associated with a primitive state token.


MutableArray (MutableArray# s a) 

newArray :: PrimMonad m => Int -> a -> m (MutableArray (PrimState m) a)Source

Create a new mutable array of the specified size and initialise all elements with the given value.

readArray :: PrimMonad m => MutableArray (PrimState m) a -> Int -> m aSource

Read a value from the array at the given index.

writeArray :: PrimMonad m => MutableArray (PrimState m) a -> Int -> a -> m ()Source

Write a value to the array at the given index.

indexArray :: Array a -> Int -> aSource

Read a value from the immutable array at the given index.

indexArrayM :: Monad m => Array a -> Int -> m aSource

Monadically read a value from the immutable array at the given index. This allows us to be strict in the array while remaining lazy in the read element which is very useful for collective operations. Suppose we want to copy an array. We could do something like this:

 copy marr arr ... = do ...
                        writeArray marr i (indexArray arr i) ...

But since primitive arrays are lazy, the calls to indexArray will not be evaluated. Rather, marr will be filled with thunks each of which would retain a reference to arr. This is definitely not what we want!

With indexArrayM, we can instead write

 copy marr arr ... = do ...
                        x <- indexArrayM arr i
                        writeArray marr i x

Now, indexing is executed immediately although the returned element is still not evaluated.

unsafeFreezeArray :: PrimMonad m => MutableArray (PrimState m) a -> m (Array a)Source

Convert a mutable array to an immutable one without copying. The array should not be modified after the conversion.

unsafeThawArray :: PrimMonad m => Array a -> m (MutableArray (PrimState m) a)Source

Convert an immutable array to an mutable one without copying. The immutable array should not be used after the conversion.

sameMutableArray :: MutableArray s a -> MutableArray s a -> BoolSource

Check whether the two arrays refer to the same memory block.