Safe Haskell | Safe-Inferred |
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If you have a `Traversable`

instance of a record,
you can load and store all elements,
that are accessible by `Traversable`

methods.
We treat the record like an array,
that is we assume, that all elements have the same size and alignment.

Example:

import Foreign.Storable.Traversable as Store data Stereo a = Stereo {left, right :: a} instance Functor Stereo where fmap = Trav.fmapDefault instance Foldable Stereo where foldMap = Trav.foldMapDefault instance Traversable Stereo where sequenceA ~(Stereo l r) = liftA2 Stereo l r instance (Storable a) => Storable (Stereo a) where sizeOf = Store.sizeOf alignment = Store.alignment peek = Store.peek (error "instance Traversable Stereo is lazy, so we do not provide a real value here") poke = Store.poke

You would certainly not define the `Traversable`

and according instances
just for the implementation of the `Storable`

instance,
but there are usually similar applications
where the `Traversable`

instance is useful.

- alignment :: (Foldable f, Storable a) => f a -> Int
- sizeOf :: (Foldable f, Storable a) => f a -> Int
- peek :: (Traversable f, Storable a) => f () -> Ptr (f a) -> IO (f a)
- poke :: (Foldable f, Storable a) => Ptr (f a) -> f a -> IO ()
- peekApplicative :: (Applicative f, Traversable f, Storable a) => Ptr (f a) -> IO (f a)

# Documentation

peek :: (Traversable f, Storable a) => f () -> Ptr (f a) -> IO (f a)Source

`peek skeleton ptr`

fills the `skeleton`

with data read from memory beginning at `ptr`

.
The skeleton is needed formally for using `Traversable`

.
For instance when reading a list, it is not clear,
how many elements shall be read.
Using the skeleton you can give this information
and you also provide information that is not contained in the element type `a`

.
For example you can call

peek (replicate 10 ()) ptr

for reading 10 elements from memory starting at `ptr`

.

peekApplicative :: (Applicative f, Traversable f, Storable a) => Ptr (f a) -> IO (f a)Source

Like `peek`

but uses `pure`

for construction of the result.
`pure`

would be in class `Pointed`

if that would exist.
Thus we use the closest approximate `Applicative`

.