derive-storable: Derive Storable instances with GHC.Generics.

This is a package candidate release! Here you can preview how this package release will appear once published to the main package index (which can be accomplished via the 'maintain' link below). Please note that once a package has been published to the main package index it cannot be undone! Please consult the package uploading documentation for more information.

[maintain] [Publish]

Derive Storable instances with GHC.Generics. The derived Storable instances have the same alignment as C structs.


[Skip to Readme]

Properties

Versions 0.1.0.0, 0.1.0.1, 0.1.0.2, 0.1.0.3, 0.1.0.4, 0.1.0.5, 0.1.0.6, 0.1.1.0, 0.1.1.1, 0.1.2.0, 0.2.0.0, 0.3.0.0, 0.3.1.0, 0.3.1.0
Change log ChangeLog.md
Dependencies base (>=4.8 && <5) [details]
License MIT
Author Mateusz Kloczko
Maintainer mateusz.p.kloczko@gmail.com
Category Foreign
Home page https://www.github.com/mkloczko/derive-storable/
Source repo head: git clone https://github.com/mkloczko/derive-storable -b master
Uploaded by mkloczko at 2022-04-09T09:07:35Z

Modules

[Index] [Quick Jump]

Flags

Automatic Flags
NameDescriptionDefault
sumtypes

Enable support for non-recursive sum types.

Disabled

Use -f <flag> to enable a flag, or -f -<flag> to disable that flag. More info

Downloads

Maintainer's Corner

Package maintainers

For package maintainers and hackage trustees


Readme for derive-storable-0.3.1.0

[back to package description]

Introduction

Build Status

The derive-storable package allows you to automatically generate Storable instances for your datatypes. It uses GHC.Generics, which allows the coders to derive certain instances automatically. To derive a (G)Storable instance, the data-type has to:

Sum types

To enable support for sum types, add a -f sumtypes option to cabal new-build or cabal new-configure. The library discerns between sum and non-sum types. Non-sum types have the same memory layout as C structs, while sum types correspond to tagged unions:

struct datatype {
    unsigned char tag;
    union { 
        constructor1 a;
        constructor2 b;
        ...
    } val;
};

Note - while it is possible to have an instance for a self/mutually recursive data-type, using methods for the data-type will result in infinite loop. So there is no support for recursion in data-types.

Note on performance

There are some problems with performance of derived Storable instances. For now there exists a solution in form of GHC Core plugin - derive-storable-plugin.

Usage

Here's an example:

{-# LANGUAGE DeriveGeneric #-}

import Foreign.Storable
import Foreign.Storable.Generic
import Foreign.Ptr
import Foreign.Marshal.Alloc

import Generics.Deriving

data Position = Position {
   x :: Double, 
   y :: Double
} deriving (Show,Read, Generic)

instance GStorable Position

updatePosition :: Ptr Position -> Position -> IO ()
updatePosition ptr pos = poke ptr pos


main = do
    let val = Position 0.0 10.0
    ptr <- malloc :: IO (Ptr Position)      
    putStrLn "Created a ptr with value of"
    putStrLn =<< show <$> peek ptr
    updatePosition ptr val
    putStrLn "And now the value of ptr is:"   
    putStrLn =<< show <$> peek ptr