Dynamic link libraries, Win32 DLLs, Win32 On Win32 platforms, the compiler is capable of both producing and using dynamic link libraries (DLLs) containing ghc-compiled code. This section shows you how to make use of this facility. The default on Win32 platforms is to link applications in such a way that the executables will use the Prelude and system libraries DLLs, rather than contain (large chunks of) them. This is transparent at the command-line, so sh$ cat main.hs module Main where main = putStrLn "hello, world!" sh$ ghc -o main main.hs ghc: module version changed to 1; reason: no old .hi file sh$ strip main.exe sh$ ls -l main.exe -rwxr-xr-x 1 544 everyone 6144 May 3 17:11 main.exe* sh$ ./main hello, world! sh$ will give you a binary as before, but the main.exe generated will use the Prelude and RTS DLLs instead. 6K for a "hello, world" application---not bad, huh? :-) If you want to build an executable that doesn't depend on any ghc-compiled DLLs, use the -static option to link in the code statically. Notice that you cannot mix code that has been compiled with -static and not, so you have to use the -static option on all the Haskell modules that make up your application. Creating a Win32 DLL --mk-dll Sealing up your Haskell library inside a DLL is quite straightforward; compile up the object files that make up the library, and then build the DLL by issuing the following command: ghc --mk-dll -o HSsuper.dll A.o Super.o B.o libmine.a -lgdi32 By feeding the ghc compiler driver the option --mk-dll, it will build a DLL rather than produce an executable. The DLL will consist of all the object files and archives given on the command line. A couple of things to notice: Since DLLs correspond to packages (see ) you need to use -package-name dll-name when compiling modules that belong to a DLL. If you don't, Haskell code that calls entry points in that DLL will do so incorrectly, and a crash will result. By default, the entry points of all the object files will be exported from the DLL when using --mk-dll. Should you want to constrain this, you can specify the module definition file to use on the command line as follows: ghc --mk-dll -o .... -optdll--def -optdllMyDef.def See Microsoft documentation for details, but a module definition file simply lists what entry points you want to export. Here's one that's suitable when building a Haskell COM server DLL: EXPORTS DllCanUnloadNow = DllCanUnloadNow@0 DllGetClassObject = DllGetClassObject@12 DllRegisterServer = DllRegisterServer@0 DllUnregisterServer = DllUnregisterServer@0 In addition to creating a DLL, the --mk-dll option will also create an import library. The import library name is derived from the name of the DLL, as follows: DLL: HScool.dll ==> import lib: libHScool_imp.a The naming scheme may look a bit weird, but it has the purpose of allowing the co-existence of import libraries with ordinary static libraries (e.g., libHSfoo.a and libHSfoo_imp.a. Additionally, when the compiler driver is linking in non-static mode, it will rewrite occurrence of -lHSfoo on the command line to -lHSfoo_imp. By doing this for you, switching from non-static to static linking is simply a question of adding -static to your command line.