如何在 Haskell 中调用 Ptr GLubyte -> IO() 类型的 function

Question

In the OpenGL Raw library is the following function:

glPolygonStipple :: Ptr GLubyte -> IO ()

The C counterpart to this function accepts a pointer to an array, but how can I call this function with an array/list in a Haskell program?

Answer 1

You'll use mallocArray to allocate memory and pokeArray to put your list into it:

http://hackage.haskell.org/packages/archive/base/latest/doc/html/Foreign-Marshal-Array.html#v:mallocArray

Something like:

do
  arrayOfGLuBytes <- (mallocArray 15) :: IO (Ptr GLubyte)
  pokeArray arrayOfGLuBytes [1,2,3,4]
  glPolygonStipple arrayOfGLuBytes
  free arrayOfGLuBytes -- free from Foreign.Marshall.Alloc

Answer 2

Probably best way to go in this situation is storable vectors in the vector package [http://hackage.haskell.org/packages/archive/vector/0.7.1/doc/html/Data-Vector-Storable.html][1]. Package provide rich interface for both immutable and mutable vectors so don't have to create vectors inside IO monad. Besides lists are linked list and conversion to arrays inovlve copying

You particular example could looks like

let myVector = fromList [1,2,3,4] 
in unsafeWith myVector glPolygonStipple