This is a version of the Get monad for incremental parsing. The parser is written as if a single, huge, strict ByteString was to be parsed. It produces results as it parses by calling yield.

However, if the parser runs out of data, rather than failing the caller sees a Partial result, which includes the list of yielded values so far and a continuation. By calling the continuation with more data, the parser continues, none the wiser.

Take the following example

 testParse = do
   getWord16be >>= yield
   testParse

 test = runGet testParse $ B.pack [1,0,0]

Here, testParse never completes, but yields Word16 values forever. It's started with a 3 byte ByteString and will yield a single value before running out of data. Thus, test = Partial cont [256]. Calling cont with a single extra byte will yield another Word16 value etc.

The lookahead functions have been removed from this parser because of their incompatibility with the incremental monad at the moment.