Somebody claiming to be Simon Peyton-Jones wrote:
| It so happens that on 64 bit OS X, haskell's Int is 64 bits, while C's | int is | 32 bits. hsc2hs's #poke does no typechecking at all, so if you have | | (#poke Struct, int_field) structp int -- where int :: Int
One should not do this. That said, the tool should not allow this.
| It's probably not even correct to | assume Double = CDouble and Float = CFloat, though it seems likely to be | always true.
base has a configure check for these, but I have been unable to determine what it does. It fails on my QNXNTO cross-compiler and so I've been manually hacking this assumption in there, but ... yeah ... probably not safe.
| I carefully vetted all my #pokes but I'm annoyed that hsc2hs and Foreign | let me get away with this. If Storable is for marshalling types to and | from C, then non-C types should not be Storable!
Well, except that you might just be round-tripping some Haskell data through (void*) in C, and so the interpretation on the C side does not matter in that case.
| While we're at it, fromIntegral is not a safe way to convert a haskell | type to a C one. But it sure is a tempting one
It is the one I always use, but I'm very aware that the behaviour is likely to be bad. That said, the behaviour of `fromIntegral` moving to a smaller type is always bad. This should probably exist:
fromIntegralSafe :: (Integral a, Ord a, Bounded b, Integral b) => a -> Maybe b
fromIntegralSafe x
| toInteger x > toInteger (maxBound `asTypeOf` v) = Nothing
| toInteger x < toInteger (minBound `asTypeOf` v) = Nothing
| otherwise = Just v
where
v = fromIntegral x
| Or maybe I shouldn't be using hsc2hs in the first place.
Hard to say. I've used it a couple times, mostly when there are C enums involved. Usually in my FFI work I just write the imports by hand (though this also allows for dangerously writing `Int` when you mean `CInt`, etc).
-- Stephen Paul Weber, @singpolyma See <http://singpolyma.net> for how I prefer to be contacted edition right joseph
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