HCoop / hcoop / debian / mlton.git / blame
| Commit | Line | Data |
|---|---|---|
| 7f918cf1 CE |
1 | CallingFromSMLToCFunctionPointer |
| 2 | ================================ | |
| 3 | ||
| 4 | Just as MLton can <:CallingFromSMLToC:directly call C functions>, it | |
| 5 | is possible to make indirect function calls; that is, function calls | |
| 6 | through a function pointer. MLton extends the syntax of SML to allow | |
| 7 | expressions like the following: | |
| 8 | ---- | |
| 9 | _import * : MLton.Pointer.t -> real * char -> int; | |
| 10 | ---- | |
| 11 | This expression denotes a function of type | |
| 12 | [source,sml] | |
| 13 | ---- | |
| 14 | MLton.Pointer.t -> real * char -> int | |
| 15 | ---- | |
| 16 | whose behavior is implemented by calling the C function at the address | |
| 17 | denoted by the `MLton.Pointer.t` argument, and supplying the C | |
| 18 | function two arguments, a `double` and an `int`. The C function | |
| 19 | pointer may be obtained, for example, by the dynamic linking loader | |
| 20 | (`dlopen`, `dlsym`, ...). | |
| 21 | ||
| 22 | The general form of an indirect `_import` expression is: | |
| 23 | ---- | |
| 24 | _import * attr... : cPtrTy -> cFuncTy; | |
| 25 | ---- | |
| 26 | The type and the semicolon are not optional. | |
| 27 | ||
| 28 | ||
| 29 | == Example == | |
| 30 | ||
| 31 | This example uses `dlopen` and friends (imported using normal | |
| 32 | `_import`) to dynamically load the math library (`libm`) and call the | |
| 33 | `cos` function. Suppose `iimport.sml` contains the following. | |
| 34 | ||
| 35 | [source,sml] | |
| 36 | ---- | |
| 37 | sys::[./bin/InclGitFile.py mlton master doc/examples/ffi/iimport.sml] | |
| 38 | ---- | |
| 39 | ||
| 40 | Compile and run `iimport.sml`. | |
| 41 | ---- | |
| 42 | % mlton -default-ann 'allowFFI true' \ | |
| 43 | -target-link-opt linux -ldl \ | |
| 44 | -target-link-opt solaris -ldl \ | |
| 45 | iimport.sml | |
| 46 | % iimport | |
| 47 | Math.cos(2.0) = ~0.416146836547 | |
| 48 | libm.so::cos(2.0) = ~0.416146836547 | |
| 49 | ---- | |
| 50 | ||
| 51 | This example also shows the `-target-link-opt` option, which uses the | |
| 52 | switch when linking only when on the specified platform. Compile with | |
| 53 | `-verbose 1` to see in more detail what's being passed to `gcc`. | |
| 54 | ||
| 55 | ||
| 56 | == Download == | |
| 57 | * <!RawGitFile(mlton,master,doc/examples/ffi/iimport.sml)> |