encodeMany is missing

[kvanbere]

I've found myself desiring a version of encode which hides the argument in the Proxy, that is, in the same way decodeMany takes a Producer, encodeMany would take a Consumer and repeatedly encode, sending the result downstream.

[k0001]

The reason encodeMany is not provided is because encode is flexible and straightforward to use for various purposes, including the one you ask about.

Taking a Consumer as an argument is not really idiomatic within Pipes, there are better ways to use input from upstream. For example, you can use for and cat together with a “loop body” to build a new Proxy consuming input from upstream and possibly producing more output.

>>> :t encode
encode
  :: (Monad m, Binary b) => b -> Producer' ByteString m ()

>>> :t for
for
  :: Monad m =>
     Proxy x' x b' b m a'
     -> (b -> Proxy x' x c' c m b') -> Proxy x' x c' c m a'

>>> :t cat
cat :: Monad m => Pipe a a m r

>>> :t for cat
for cat
  :: Monad m => (b -> Proxy () b c' c m ()) -> Proxy () b c' c m a'

>>> :t for cat encode
for cat encode
  :: (Monad m, Binary b) => Proxy () b () ByteString m a'
  -- simplified type: 
  --   :: (Monad m, Binary b) => Pipe b ByteString m a' 

>>> runEffect $ each [1,2] >-> for cat encode >-> P.print
"\NUL\NUL\NUL\NUL\SOH"
"\NUL\NUL\NUL\NUL\STX"

Or you can use (~>) to compose those “loop bodies” directly:

>>> :t (~>)
(~>)
  :: Monad m =>
     (a -> Proxy x' x b' b m a')
     -> (b -> Proxy x' x c' c m b') -> a -> Proxy x' x c' c m a'

>>> :t (encode ~>)
(encode ~>)
  :: (Monad m, Binary a) =>
     (ByteString -> Proxy x' x c' c m ()) -> a -> Proxy x' x c' c m ()

>>> :t encode ~> lift . print
encode ~> lift . print :: Binary a => a -> Proxy x' x c' c IO ()

>>> runEffect $ for (each [1,2]) $ encode ~> lift . print
"\NUL\NUL\NUL\NUL\SOH"
"\NUL\NUL\NUL\NUL\STX"

Does this help?

[kvanbere]

Hi,

Thanks for that. Makes a lot of sense now.

It would be nice if you were to include a brief version of this explanation in the documentation for pipes-binary somewhere.

Regards.

[k0001]

The reason I didn't mention this in the documentation is because Pipes.Tutorial talks about a lot about it. But you are right, adding an example or two to the documentation wouldn't hurt. I'll add that, thanks.