On 26/06/2017 08:18, Sylvain Henry wrote:
Hi,
I would use IORef and StablePtr:
import Foreign.StablePtr import Foreign.Ptr import Data.IORef
type H5Iterate = Hid -> CString -> Ptr () -> Ptr () -> IO ()
-- see https://wiki.haskell.org/Foreign_Function_Interface#Function_pointers foreign import ccall "wrapper" mkOp :: H5Iterate -> FunPtr (H5Iterate)
foreign import ccall "H5Lvisit" h5iterate :: Hid -> Index -> Order -> FunPtr H5Iterate -> Ptr () -> IO ()
main = do state <- newIORef [] statePtr <- newStablePtr state
let callback :: H5Iterate callback hid name infoptr dataptr = do -- get the state stRef <- deRefStablePtr (castPtrToStablePtr dataptr) st <- readIORef stRef -- compute the new state newSt <- ... -- store the new state writeIORef stRef newSt
h5iterate gid idttyp order (mkOp callback) (castStablePtrToPtr statePtr)
Don't forget to: freeStablePtr statePtr
-- retrieve the final state finalState <- readIORef state
- Sylvain
On 24/06/2017 15:47, PICCA Frederic-Emmanuel wrote:
Hello
I would like to create a binding for this function [1].
herr_t H5Literate( hid_t group_id, H5_index_t index_type, H5_iter_order_t order, hsize_t *idx, H5L_iterate_t op, void *op_data )
My "only" problem is with the op and op_data part. Here the C op signature[2]
op -> herr_t (*H5L_iterate_t)( hid_t g_id, const char *name, const H5L_info_t *info, void *op_data)
What I would like to do is to create an Haskell function which allows to return what is contained under the op_data. What I understand from this is that I give the H5Literate function an op function which is executed for each group of my hdf5 file. So the op method is called with the releavant parameters. The op_data can be use to accumulate things during the traversal.
H5Literate :: Hid -> Index -> Order -> Maybe HSize -> H5Iterate -> _ -> _
type H5Iterate = Hid -> ByteString -> Info -> _ -> _
So it seems to me that I need to use a State inorder to do the accumulation.
For exemple,I want to collect each group names and accumulate then in a list.
Somy questioniswhat should be the signature of both function.
I have also the fealing that the return type MUST have a Storableinstance.
Thanks for your help
Frederic
[1] https://support.hdfgroup.org/HDF5/doc/RM/RM_H5L.html#Link-Iterate [2] https://support.hdfgroup.org/HDF5/doc/RM/RM_H5L.html#Link-Visit _______________________________________________ Beginners mailing list Beginners@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
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