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
  a <- getWord16be
  b <- getWord16be
  return $ a + b

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

Here testParse needs to read 4 bytes in order to complete, so test is a Partial, which includes the continuation function, so which you can pass more data until it completes

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