Installing GHC iOS

Download the scripts from https://github.com/ghc-ios/ghc-ios-scripts. Place them in your $PATH.
Download http://llvm.org/releases/3.0/clang+llvm-3.0-x86_64-apple-darwin11.tar.gz and place them somewhere easy to remember (e.g. /usr/local/clang-3.0/ — not in your $PATH, since you don’t want to override Xcode’s clang)
Download the GHC iOS for the device: http://www.haskell.org/ghc/dist/7.8.1-rc2/ghc-7.8.0.20140228-arm-apple-ios.tar.bz2
- Unpack it, Run configure:
```
./configure
```
- Edit the “settings” file:
  - Ensure “C compiler command” is arm-apple-darwin10-clang
  - Ensure “ld command” is arm-apple-darwin10-ld
  - Ensure “LLVM llc command” is the full path to llc from Clang+LLVM 3.0 (as downloaded above, e.g. /usr/local/clang-3.0/bin/llc)
  - Ditto for “LLVM opt command” (e.g. /usr/local/clang-3.0/bin/opt)
- Install the compiler:
```
make install
```
Download the GHC iOS for the simulator: http://www.haskell.org/ghc/dist/7.8.1-rc2/ghc-7.8.0.20140228-i386-apple-ios.tar.bz2
- Unpack it, Run configure:
```
./configure
```
- Edit the “settings” file:
  - Ensure “C compiler command” is i386-apple-darwin11-clang
  - Ensure “ld command” is i386-apple-darwin11-ld
  - Ensure “LLVM llc command” is the full path to llc from Clang+LLVM 3.0 (as downloaded above, e.g. /usr/local/clang-3.0/bin/llc)
  - Ditto for “LLVM opt command” (e.g. /usr/local/clang-3.0/bin/opt)
- Install the compiler:
```
make install
```

Using GHC iOS

Create 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

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

Create or open an Xcode project (the Single View Application template is simple for testing)
Drag Counter.a and Counter_stub.h to the project’s sidebar. Make sure “Add to Targets:” has a check next to your app.
Click on your project at the top of the Xcode sidebar.
- In the “Build Phases” tab, under “Link Binary with Libraries”, click the + and choose libiconv.dylib
- In the “Build Settings” tab:
  - Set “Architectures” to “Standard Architectures (armv7, armv7s)”, as we don’t support 64-bit yet
  - Set “Dead Code Stripping” to No
  - Add /usr/local/lib/arm-apple-darwin10-ghc-7.8.0.20140228/include/ to “Header Search Paths” (ensure this matches the date of the GHC-iOS binary you downloaded)
In your app’s AppDelegate.m:
```
#import "Counter_stub.h"
```
and at the top of application:didFinishLaunchingWithOptions:, add:
```
    hs_init(NULL, NULL);
    startCounter(3);
```
Run your app! You should see a growing triangle of ’o’s.

Using GHC iOS with Cabal

You’ll need a very recent version of Cabal: http://www.haskell.org/cabal/download.html
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 text
```
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.