[Haskell-cafe] An example of enumerator processing some data between input and output

[oleg at okmij.org]

Paul Sujkov wrote:

> I played a bit with the enumerator package, and I'm quite stuck with the
> question how to duplex data to two (or more) consumers

Many packages have the combinator named enumPair (or something like
that). Here is one example
	http://okmij.org/ftp/ftp/Streams.html#1enum2iter
The combinator is quite useful for logging, for dumping the contents
of the stream as it is being processed.

> actually I need to pipeline output of one consumer to another
> (outputting text after making some internal representation - with Show
> instance - with the parseData).

You need enumeratees, which convert one stream into another. There are
many examples of those: e.g., converting a stream of bytes into a stream
of lines, or a stream of compressed/encoded data into the plaintext
stream. You enumerator package probably has them. The Stream.html page
also describes many examples of enumeratees.