Hello
I am wrapping Fuse in a pure Haskell binding and have some issues
with the interface. Currently I am using a record for managing
the callback functions, but I think there may be a more elegant
formulation.
Any ideas how to formulate the Fuse record as a typeclass elegantly?
Some notes:
+ TFs not FDs.
+ Separate fh* implementations (raw/stableptr/custom implemented by user)
easily selected by the library user.
+ Readable type errors.
+ One large typeclass + overlapping instances works, but seems hacky.
+ MPTCs will probably work but is it good form to use them with TFs?
+ Or is using a record better currently?
ps. Note that the interface is very much simplified for the sake
of the discussion. (e.g. [Word8] instead of ByteString).
> import Data.Word
>
> data IsDir
> data IsFile
>
> type Ino = Word32
> data Attr = Attr {}
>
> data Fuse (fh :: * -> *) = Fuse {
> open :: Ino -> IO (fh IsFile)
> , read :: Ino -> fh IsFile -> Word64 -> Word32 -> IO [Word8]
> , opendir :: Ino -> IO (fh IsDir)
> , getattr :: forall fileOrDir. Ino -> fh fileOrDir -> IO Attr
> -- ...
>
> -- File handle management
> , fhFree :: Word64 -> IO ()
> , fhAlloc :: forall any. fh any -> IO Word64
> , fhRef :: forall any. Word64 -> IO (fh any)
> }
>
> -- Optimally get rid of this wrapping...
> newtype RawFH t = R { r :: Word64 }
> noFhEmpty :: Fuse RawFH
> noFhEmpty = Fuse { fhFree = \_ -> return ()
> , fhAlloc = return . r
> , fhRef = return . R
> }
>
> stablePtrEmpty :: Fuse anyfh
> stablePtrEmpty = Fuse {} -- implement fh* with StablePtrs (omitted)
>
> -- User file handle type might be like this:
>
> data Obj t where
> Dir :: {} -> Obj IsDir
> File :: {} -> Obj IsFile
- Taru Karttunen
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