On Thu, 2007-10-25 at 11:30 -0400, Graham Fawcett wrote:
Hi folks,
I'm writing a Gnu DBM module as an exercise for learning Haskell and its FFI. I'm wondering how I might write a function that returns the database keys as a lazy list. I've wrapped the two relevant foreign functions:
firstKey :: Ptr Db -> IO (Maybe String) nextKey :: Ptr Db -> String -> IO (Maybe String)
NextKey takes a key, and returns the next one. Either function could return Nothing, since the db may have 0 or 1 keys.
Given these, is it possible to write a (simple) function
allKeys :: Ptr Db -> IO [String]
that lazily fetches the keys? (Or, an idiomatic way of achieving the same end?)
Just use unsafeInterleaveIO in the obvious definition to read all the keys. That said, it's not called unsafeInterleaveIO for no reason.