On Mon, 2009-10-12 at 11:55 +0100, Duncan Coutts wrote:
> I'm getting crazy values returned as the position from
> editableInsertText.
>
> This is using the example from the Editable haddock documentation:
>
> idRef <- newIORef undefined
> id <- onInsertText entry $ \str pos -> do
> id <- readIORef idRef
> signalBlock id
> pos' <- editableInsertText entry (map toUpper str) pos
> signalUnblock id
> stopInsertText id
> return pos'
> writeIORef idRef id
>
> When I run it, the pos' returned is 129475190752018432, when inserting a
> string of length 1 at position 1. Looking at the binding code I don't
> see anything obviously wrong. This is on 64bit Linux.
>
> The fact the number is so large is suspicious. The C type is an int
> which is still 32bit even on 64bit machines. That said, the types all
> look right. c2hs generates the binding with the type Ptr CInt, and we
> use with, so it should all be ok. I'm stumped.
Uuuh, funky one.
The offending lines were:
pos <- peek posPtr
pos' <- handler str pos
poke posPtr pos'
which were located in the signal handler. The handler is actually called
with a pointer containing the old position and expects the new position
in the pointed-to int on return. However, posPtr is 'Ptr a' and becomes
'Ptr Int' because of the type of 'handler'. So this shows that Haskell
Int and CInt are not the same, even though I don't understand how this
garbage is produced. Fix:
pos <- peek (posPtr :: Ptr {#type gint#})
pos' <- handler str (fromIntegral pos)
poke (posPtr :: Ptr {#type gint#}) (fromIntegral pos')
Now in darcs,
Axel.
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