This is just what we agreed on a couple of months ago, no?
I'm afraid this has been sitting on my HDirect ToDo list since
then, as I've been busy with misc other Haskell-related matters.
However, I've unqueued the item & implemented something
which is close to what you're after, I believe. It's just
been checked into the hdirect portion of the CVS repo.
Have a go & let me know whether this scratches your
itch or not.
--sigbjorn
----- Original Message -----
From: "Mike Thomas"
Hi all.
HDirect can generate code as follows:
------------------------------------------------------------ data CONST_DDWAITVBFLAGS = DDWAITVB_BLOCKBEGIN | DDWAITVB_BLOCKBEGINEVENT | DDWAITVB_BLOCKEND
instance Prelude.Enum (CONST_DDWAITVBFLAGS) where fromEnum v = case v of DDWAITVB_BLOCKBEGIN -> 1 DDWAITVB_BLOCKBEGINEVENT -> 2 DDWAITVB_BLOCKEND -> 4
toEnum v = case v of 1 -> DDWAITVB_BLOCKBEGIN 2 -> DDWAITVB_BLOCKBEGINEVENT 4 -> DDWAITVB_BLOCKEND _ -> Prelude.error "unmarshallCONST_DDWAITVBFLAGS: illegal enum value "
------------------------------------------------------------
Unfortunately, if you want to interface to a C function which takes a combination of flags added together in a specific argument eg (C):
bar ( DDWAITVB_BLOCKBEGIN + DDWAITVB_BLOCKBEGINEVENT );
(Haskell)
bar (toEnum (fromEnum DDWAITVB_BLOCKBEGIN) + (fromEnum DDWAITVB_BLOCKBEGINEVENT ))
the toEnum function can't deal with the comnbination - it generates a run-time error.
Is there a simple way to deal with this situation (the need to associate symbols with specific values, while retaining the ability to lump the values together in a manner reflecting the underlying C semantics)?
Should there be another FFI type CEnum?
Should the Haskell Enum type be operable with +/&/| or whatever?
Merry Christmas
Mike Thomas.