Haskell dynamic library loader
==============================
Load and execute functions from Haskell dynamic libraries without being
restricted to a single RTS/GHC version.
This package consists of the initial loader executable `rts-loader` written
in plain C and a Haskell library providing a convinient interface to it. The
initial loader executable is implemented in C since writing it in Haskell would
mean linking against the RTS which means we can't load libraries compiled with
another version of GHC.
In order to get Cabal to compile a pure C executable while not linking against
the RTS still some hacks in `Setup.hs` are employed to call `gcc` directly so
beware.
Usage
-----
The example below will locate the package "foopkg" in the package databases
configured for the Cabal project in the current directory and execute the
function "main" from the module "Lib". The package can be found in
`tests/lib` in the rts-loader source tree.
To run the example, execute the following commands in the rts-loader source
tree.
```
$ cabal install --only-dependencies && cabal configure && cabal build && cabal install tests/lib
$ rts_loader_libexecdir=dist/build/rts-loader dist/build/rts-loader-example/rts-loader-example
```
`rts_loader_libexecdir=...` is only required if you didn't install rts-loader
into a sandbox or elsewhere already.
import System.Loader.RTS
import System.Process
import Distribution.Verbosity
import Distribution.Package
import Distribution.Simple.Configure
import Distribution.Simple.LocalBuildInfo
import Distribution.Simple.Configure (getPersistBuildConfig)
main :: IO ()
main = do
lbi <- getPersistBuildConfig "dist"
let verbosity = normal
comp = compiler lbi
pkg_db_stack = withPackageDB lbi
prog_conf = withPrograms lbi
pidx <- getInstalledPackages verbosity comp pkg_db_stack prog_conf
loader_exe <- loaderExecutablePath
loader_args <- loaderInvocation (SymbolIdentifier "Lib" "main") [] <$>
(resolveLibraryInfo comp [WayDyn] $
lookupLibraryInfo pidx $
PQName $ PackageName "foopkg")
print =<< rawSystem loader_exe loader_args
We use information written by `cabal configure` (see `getPersistBuildConfig`)
for convinience only this is not actually required to use the loader.