EXPERIMENTAL

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

• Only tested with linux.
• Only tested with Stack (LTS 13.26)
• 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.Core
import Foreign.C.Types

foreign export ccall "emacs_module_init" emacsModuleInit :: EmacsModule

emacsModuleInit :: EmacsModule
emacsModuleInit = emacsModule (Just "mymodule") $ do

  fun <- mkIOFun1 (readString . unsafeType) (fmap untype . mkString) $ \txt -> do
    message $ "haskell squre function called: " <> txt
    pure $ "!" <> txt <> "!"

  setCommand "great-from-haskell" InteractiveNoArgs fun

main :: IO ()
main = undefined

How to use

Explaining using Stack and LTS 13.26 as premise.

1. Create a new project with Stack

$ stack --resolver=lts-13.26 new mymodule

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

project.yaml:

executables:
  mymodule.so:
    main:                Main.hs
    source-dirs:         app
    ghc-options:
    - -threaded
    - -rtsopts
    - -with-rtsopts=-N
    dependencies:
    - mymodule
    - haskelisp

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

project.yaml:

executables:
  mymodule.so:
    main:                Main.hs
    source-dirs:         app
    cc-options:          -fPIC
    ghc-options:
    - -shared
    - -dynamic
    - -fPIC
    - -lHSrts-ghc8.6.5

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

project.yaml:

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

5. Write some code

Main.hs:

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

import Emacs.Core
import Foreign.C.Types

foreign export ccall "emacs_module_init" emacsModuleInit :: EmacsModule

emacsModuleInit :: EmacsModule
emacsModuleInit = emacsModule (Just "mymodule") $ do

  fun <- mkIOFun1 (readString . unsafeType) (fmap untype . mkString) $ \txt -> do
    message $ "haskell squre function called: " <> txt
    pure $ "!" <> txt <> "!"

  setCommand "great-from-haskell" InteractiveNoArgs fun

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 $(stk path --local-install-root)/bin/mymodule.so ~/.emacs.d/lisp/

Or you can start a clean emacs with load-path seted:

$ emacs --no-splash -q -L $(stk path --local-install-root)/bin/

8. Load your shared library from Emacs

(require 'mymodule)