Hi everybody,
I know this sounds like an issue many have faced before me, but good old
google didn't come up with any helpful results. The basic problem is
that I need to marshal a union so I can pass it to a C function via FFI.
So to make sure I have my head wrapped around this correctly, say I have
a union like so:
typedef union {
int i;
char c;
} my_union;
This would typically be represented in Haskell as:
data myUnion = I CInt | C CChar
My question is how would you marshall (define an Storable instance for)
myUnion into my_union? It's my understanding that an instance my_union
would take up sizeof(int) bytes in memory, i.e. the size of it's largest
member. So to store this we would write something along the lines of:
instance Storable myUnion where
size _ = #{size my_union} -- <-- hsc2hs shortcut
alignment _ = alignment undefined::CInt -- <-- What should this
really be?
peek ptr = do -- <-- How are you supposed to know which element to
extract?
poke ptr (I i) = poke ptr i -- <-- Or should this be #{poke
my_union, i} ptr i ?
poke ptr (C c) = poke ptr c
I hope this clear. I appreciate all the help. If this question has
already been answered, which I'm sure it has, please point me to right
spot. Thanks again for everyone's time.
Nabil Alsharif.
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