Elegant definition of Storable instances for records
With this package you can build a Storable instance of a record type
from Storable instances of its elements in an elegant way. It does not
do any magic, just a bit arithmetic to compute the right offsets, that
would be otherwise done manually or by a preprocessor like C2HS. I
cannot promise that the generated memory layout is compatible with
that of a corresponding C struct. However, the module generates the
smallest layout that is possible with respect to the alignment of the
record elements. If you encounter, that a record does not have a
compatible layout, we should fix that. But also without C
compatibility this package is useful e.g. in connection with
StorableVector.
We provide Storable instance support for several cases:
- If you wrap a type in a newtype, then you can lift its
Storable instance to that newtype with the module
Foreign.Storable.Newtype. This way you do not need the
GeneralizedNewtypeDeriving feature of GHC.
- If you have a type that is an instance of Traversable, you
can use that feature for implementation of Storable methods.
The module Foreign.Storable.Traversable allows manipulation of
the portion of your type, that is accessible by Traversable
methods. For instance with the type data T a = Cons Int [a]
and an according Traversable implementation, you can load and
store the elements of the contained list. This may be part of a
Storable implementation of the whole type.
- If you have a record containing elements of various types, then
you need module Foreign.Storable.Record.
Note however that the Storable instances defined with this package are
quite slow in (up to) GHC-6.12.1. I'm afraid this is due to incomplete
inlining, but we have still to investigate the problem.
For examples see packages
storable-tuple and
sample-frame.