Installing GHC iOS

• Prerequisites:

  • Install Xcode http://itunes.apple.com/us/app/xcode/id497799835
  • Update Cabal with cabal update && cabal install cabal-install
    • Remove jobs: $ncpus from ~/.cabal/config if it's there
  • Download these scripts and place them in your PATH. For example:

    git clone git@github.com:ghc-ios/ghc-ios-scripts.git ~/bin/ghc-ios-scripts
    echo -e "\nPATH=~/bin/ghc-ios-scripts:"'$PATH' >> ~/.profile
    PATH=~/bin/ghc-ios-scripts:$PATH

• Run the installer script. GHC iOS will politely live alongside your existing native GHC installation.

  installGHCiOS.sh

Using GHC iOS

• Create or open an Xcode project (the Single View Application template is simple for testing)

• Use this repository's HaskelliOS.xcconfig

  • From the File menu, click "Add Files to..." Select HaskelliOS.xcconfig. It doesn't need to be added to any targets.
  • Click on your project at the top of the Xcode navigator sidebar.
  • Within the editing window, make sure your project is selected, not the target. (The selector is located to the left of the tabs.)
  • In the "Info" tab, under "Configuration", expand each configuration and choose HaskelliOS.
  • You may need to edit HaskelliOS.xcconfig and adjust HEADER_SEARCH_PATHS to match your installed GHC.

• Compile your Haskell code with ghc-ios. For example, if you had a file named Counter.hs:

  {-# LANGUAGE ForeignFunctionInterface #-}
  module Counter where
  import Control.Concurrent
  import Control.Monad
  foreign export ccall startCounter :: Int -> IO ()
  startCounter :: Int -> IO ()
  startCounter = void . forkIO . void . loop
  where loop i = do
          putStrLn (replicate i 'o')
          threadDelay (10^6)
          loop (i + 1)

• Compile this like so to get Counter.a and Counter_stub.h:

  ghc-ios Counter.hs

  (Counter.a will be a fat binary that works with both devices and the simulator.)

• Drag Counter.a and Counter_stub.h to the project's sidebar. Make sure "Add to Targets:" has a check next to your app.

• In main.m #import "HsFFI.h" and add hs_init(NULL, NULL); to the top of main()

• In your app's AppDelegate.m:

  #import "Counter_stub.h"

• and at the top of application:didFinishLaunchingWithOptions:, add:

  startCounter(3);

• Run your app! You should see a growing triangle of 'o's.

• To automatically rebuild your Haskell file each time you rebuild your project:

  • Click your project at the top of the Xcode sidebar, then click on your app under Targets on the left.
  • Click the "Build Phases" tab, then click the + at the top left and choose "New Run Script Build phase"
  • Drag the new Run Script build phase to the top of the list.
  • Enter:

    source ~/.profile # or ~/.bash_profile, whichever you use
    ghc-ios Counter

    Xcode will now run these commands each time it builds your project.

Using GHC iOS with Cabal

• You'll need a very recent version of Cabal: cabal install cabal-install
• You'll also need to check that the option jobs: $ncpus does not appear in your ~/.cabal/config file, as it triggers a mode that does not support cross-compilation.
• To install a package for the device and simulator, use cabal-ios (included in ghc-ios-scripts) like:

  cabal-ios install random

• You should now be able to use the package in a file compiled with ghc-ios. The package will be statically linked into the .a library.

Troubleshooting

• If you run into Illegal instruction: 4 while running make install, please see this discussion https://github.com/ghc-ios/ghc-ios-scripts/issues/4 — we're not sure what causes it yet but the thread contains a working solution.

• Some packages need a flag to make them use integer-simple rather than trying to use integer-gmp, for example

  cabal-ios install -finteger-simple text

  and

  cabal-ios install -f-integer-gmp hashable

• Similarly, some packages need to have Template Haskell disabled, such as

  cabal-ios install -f-templateHaskell QuickCheck

  and

  cabal-ios install distributed-process --flags=-th

You can check the .cabal file to find the appropriate option.

• For packages that use executables, there's not yet a flag to give to Cabal to keep it from trying and failing to build them (for example, Crypto and pretty-show). Until that flag is implemented, you'll have to use cabal get and manually comment out the executables section in the .cabal file, then cabal install'ing the edited copy. You can use this strategy to get rid of Template Haskell in packages that don't provide a flag to do so, such as aeson. But consider submitting a patch to the developers : )