concat package:streaming-bytestring -is:exact

concat :: Monad m => Stream (ByteStream m) m r -> ByteStream m r
streaming-bytestring Streaming.ByteString Streaming.ByteString.Char8
O(n) Concatenate a stream of byte streams.
concatBuilders :: Stream (Of Builder) IO () -> Builder
streaming-bytestring Streaming.ByteString Streaming.ByteString.Char8
Concatenate a stream of builders (not a streaming bytestring!) into a single builder. 
>>> let aa = yield (integerDec 10000) >> yield (string8 " is a number.") >> yield (char8 '\n')

>>> hPutBuilder IO.stdout $ concatBuilders aa
10000 is a number.