feat(bindings/haskell): support list and scan

[silver-ymz]

Update:

• export list and scan
• add tests for copy, rename, list, scan
• fix error of trailling \0 in leak_str
• refactor OpMonad from custom type to type synonym in order to provide more available ways

I imitate DirStream in unix library to design Lister API. However, it doesn't seem very native and useful. I havn't came up with other solutions about it yet. Maybe we can improve it in the future.

[Xuanwo]

I imitate DirStream in unix library to design Lister API. However, it doesn't seem very native and useful. I havn't came up with other solutions about it yet. Maybe we can improve it in the future.

How will haskell handle similiar works?

[silver-ymz]

These are unix library API for DirStream.

openDirStream :: RawFilePath -> IO DirStream
readDirStream :: DirStream -> IO RawFilePath

It seems only to provide an iterator and next function.

These are the APIs I exported.

listOpRaw :: Operator -> String -> IO (Either OpenDALError Lister)
nextLister :: Lister -> IO (Either OpenDALError (Maybe String))
allLister :: Lister -> IO (Either OpenDALError [String])

list operation will return a Lister and we provide next and all operation for it.

The API I'm expecting is like ListT in pipe library. With it, users can use all standard library utilities like map, filter, etc. I may need to spend more time researching it.

[Xuanwo]

we provide next and all operation for it.

Provide all on Lister is wrong since the Lister could be very large (more than 1M objects). It's by design that only has a next function.

[silver-ymz]

I have removed all operation. Could you review again?

[Xuanwo]

Thanks!