Elegant definition of Storable instances for records

LTS Haskell 9.1:
Stackage Nightly 2017-08-17:
Latest on Hackage:
BSD3 licensed and maintained by Henning Thielemann

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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.

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