[Haskell] [ANNOUNCE] dynamic-linker-template: automatically derive dynamic linking methods from a data type.

Sylvain HENRY hsyl20 at gmail.com
Thu Aug 2 18:08:15 CEST 2012


A few days ago I uploaded on Hackage the first release of 
dynamic-linker-template package (System.Posix.DynamicLinker.Template). 
Basically, it uses Template Haskell to generate boilerplate code to 
dynamically load symbols of a shared library into a data defined using 
"record" syntax.

Simple example:

{-# LANGUAGE TemplateHaskell, ForeignFunctionInterface #-}

import System.Posix.DynamicLinker.Template

data MyLib = MyLib {
     -- Mandatory field (name and type)
     libHandle :: DL,

     -- Mandatory symbol. Will throw an exception if not available
     myFunction1 :: Int -> Float,

      -- Optional symbol
     myFunction2 :: Maybe (Int -> Int)

$(makeDynamicLinker ''MyLib CCall 'id)

-- Use any String->String function instead of "id" to transform field 
names into symbol names

-- The following function will be generated:
-- loadMyLib :: FilePath -> [RTLDFlags] -> IO MyLib

main = do
     lib <- loadMyLib "mylib.so" [RTLD_NOW,RTLD_LOCAL]
     putStrLn $ show (myFunction1 lib 10)


For a real world example (with the OpenCL library), see [1]. I don't use 
optional symbols yet but I will as I need to support different OpenCL 
versions that expose different symbols (some become deprecated and new 
releases add new ones). I use a custom function to transform field names 
into symbol names (to strip prefix). This functionality will also be 
useful with CUDA library which appends "_v2" to every symbol in recent 

Do not hesitate to report any bug or suggestion.



Sylvain Henry
CS PhD Student at INRIA/LaBRI
University of Bordeaux (France)
sylvain.henry at inria.fr

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