EXPERIMENTAL

Write Emacs module in Haskell, using Emacs 25's Dynamic Module feature.

• Only tested with linux.
• Only tested with Stack (LTS 6.26)
• You need to build emacs with --with-modules configuration options
• You need to specify some ghc-options to make it work

Sample:

{-# LANGUAGE ForeignFunctionInterface,OverloadedStrings #-}
module Main where

import Emacs
import Foreign.C.Types

foreign export ccall "emacs_module_init" emacsModuleInit :: EmacsModule

emacsModuleInit :: EmacsModule
emacsModuleInit = defmodule "sample-module" $ do

  setVal "foo" (Symbol "bar")

  defun "square" $ \i -> do
    message "haskell squre function called"
    return $ (i*i :: Int)

main :: IO ()
main = undefined

How to use

Explain using Stack and LTS 6.26 as premise.

1. Create a new project with Stack

$ stack --resolver=lts-6.26 new mymodule

2. Change executable name to *.so and add haskelisp to the dependency

mymodule.cabal:

executable mymodule.so
  hs-source-dirs:      app
  main-is:             Main.hs
  ghc-options:         -threaded -rtsopts -with-rtsopts=-N
  build-depends:       base
                     , mymodule
                     , haskelisp
  default-language:    Haskell2010

3. Change ghc-options and add cc-options to make shared library

mymodule.cabal:

executable mymodule.so
  ...
  cc-options:          -fPIC
  ghc-options:         -shared -dynamic -fPIC -lHSrts-ghc7.10.3
  ...

4. Modules must be GPL compatible

The shared library must include plugin_is_GPL_compatible symbol to be loaded by Emacs. Prepare a C source file and specify it with c-sources option.

$ echo 'int plugin_is_GPL_compatible;' > plugin_is_GPL_compatible.c

mymodule.cabal:

executable mymodule.so
  ...
  c-sources:           plugin_is_GPL_compatible.c
  ...

5. Write some code

Main.hs:

{-# LANGUAGE ForeignFunctionInterface,OverloadedStrings #-}
module Main where

import Emacs
import Foreign.C.Types

foreign export ccall "emacs_module_init" emacsModuleInit :: EmacsModule

emacsModuleInit :: EmacsModule
emacsModuleInit = defmodule "mymodule" $ do

  defun "mysquare" $ \i -> do
    message "haskell squre function called"
    return $ (i*i :: Int)

main :: IO ()
main = undefined

We don't need main function, but without it cause a compile error, so include a dummy one. It won't be called.

6. Build

$ stack build

7. Copy the genereated shared library under load-path

For example, if ~/.emacs.d/lisp is included in load-path:

$ cp .stack-work/install/x86_64-linux/lts-6.26/7.10.3/bin/mymodule.so ~/.emacs.d/lisp/

8. Load your shared library

(require 'mymodule)