This is a sample project that is used to demonstrate how to create a
shared library in Haskell that can be called from other programs.
E.g: python using ctypes, or C using dlopen.

This is currently tested and working with OS X Snow Leopard with 7.4.2
running Haskell Platform 2012.4.0.0 64-bit.

To use:

  $ sh build-test.sh 1
  $ python test.py

build-test.sh contains a number of potential ways in which you could compile
a shared library (currently method '1' works correctly).

test.py uses ctypes to import and call the functions in the haskell shared library.

Test.hs contains some example functions.


Historical tests:

Previously there were problems on earlier version of the Haskell platform.
These experiments are documented below.

Tests:

1) OS X Snow Leopard GHC 7.0.4 from Haskell Platform 2011.4.0.0 64 bit

Build method #1:

  [1 of 1] Compiling Test             ( Test.hs, Test.o )
  Linking Test.so ...
  Undefined symbols:
    "_environ", referenced from:
        ___hscore_environ in libHSbase-4.3.1.0.a(PrelIOUtils.o)
       (maybe you meant: ___hscore_environ)
  ld: symbol(s) not found
  collect2: ld returned 1 exit status

Build method #2:

Implicit import declaration:
    Could not find module `Prelude':
      Perhaps you haven't installed the "dyn" libraries for package `base'?
      Use -v to see a list of the files searched for.

Build method #3:

Implicit import declaration:
    Could not find module `Prelude':
      Perhaps you haven't installed the "dyn" libraries for package `base'?
      Use -v to see a list of the files searched for.

Build method #4:

[1 of 1] Compiling Test             ( Test.hs, Test.o )
Linking libTest.so ...
ld: pointer in read-only segment not allowed in slidable image, used in ___gmpn_modexact_1c_odd from /usr/local/lib/ghc-7.0.4/integer-gmp-0.2.0.3/libHSinteger-gmp-0.2.0.3.a(mode1o.o)
collect2: ld returned 1 exit status

Build method #5:

Implicit import declaration:
    Could not find module `Prelude':
      Perhaps you haven't installed the "dyn" libraries for package `base'?
      Use -v to see a list of the files searched for.

Build method #6:

[1 of 1] Compiling Test             ( Test.hs, Test.o )
Linking libTest.so ...
ld: pointer in read-only segment not allowed in slidable image, used in ___gmpn_modexact_1c_odd from /usr/local/lib/ghc-7.0.4/integer-gmp-0.2.0.3/libHSinteger-gmp-0.2.0.3.a(mode1o.o)
collect2: ld returned 1 exit status

2) OS X Snow Leopard GHC 7.0.4 from Haskell Platform 2011.4.0.0 32 bit

Build method #1:

[1 of 1] Compiling Test             ( Test.hs, Test.o )
Linking Test.so ...
Undefined symbols:
  "_environ", referenced from:
      _environ$non_lazy_ptr in libHSbase-4.3.1.0.a(PrelIOUtils.o)
     (maybe you meant: ___hscore_environ, _environ$non_lazy_ptr )
ld: symbol(s) not found
collect2: ld returned 1 exit status

Build method #2:

benno@ff:~/haskell-shared-example% sh build-test.sh 2
[1 of 1] Compiling Test             ( Test.hs, Test.o )
Linking Test.so ...
ld: unknown option: -optc
collect2: ld returned 1 exit status

Build method #3:

benno@ff:~/haskell-shared-example% sh build-test.sh 3
[1 of 1] Compiling Test             ( Test.hs, Test.o )
Linking libTest.so ...

Success! in linking:

But, load time error:

Library not loaded: /usr/local/lib/ghc-7.0.4/base-4.3.1.0/libHSbase-4.3.1.0-ghc7.0.4.dylib

Build method #4:

Success in linking, but loading error:

OSError: dlopen(./libTest.so, 6): Symbol not found: _alloc_blocks_lim
  Referenced from: /Volumes/BigDisk/Users/benno/haskell-shared-example/libTest.so
  Expected in: flat namespace

Build method #5:

Success in linking, but loading error:

OSError: dlopen(./libTest.so, 6): Library not loaded: /usr/local/lib/ghc-7.0.4/base-4.3.1.0/libHSbase-4.3.1.0-ghc7.0.4.dylib
  Referenced from: /Volumes/BigDisk/Users/benno/haskell-shared-example/libTest.so
  Reason: image not found

Build method #6:

benno@ff:~/haskell-shared-example% sh build-test.sh 6
[1 of 1] Compiling Test             ( Test.hs, Test.o )
Linking libTest.so ...
benno@ff:~/haskell-shared-example% arch -i386 /usr/bin/python2.6  test.py
<CDLL './libTest.so', handle 20a570 at 1f0090>
<_FuncPtr object at 0x1d3af8>