Composition: use one codec after another

[sergei-shabanau]

I'm trying to understand the use case and how it can be expressed.

We have

case class Codec[I, A](eq: Equiv[I, (I, A)])

which consumes a bit of I to produce A and returns (remainder of I) + A.

We already have product operation to combine two codecs

def ~ [B](that: Codec[I, B]): Codec[I, (A, B)]

which consumes a bit of I to produce A and then consumes a bit of remainder of I to produce B and returns (what is yet remained of I) + (A, B).

I've built (see the difference in that type parameters)

def >> [B](that: Codec[A, B]): Codec[I, (A, B)]

which consumes a bit of I to produce A and then consumes a bit of A to produce B and returns (the remainder of I) + (the remainder of A) + B.

Questions:

1. Is the use case real?
2. The signature is confusing, i.e. going from I to (A, B) in both cases, and I believe product is the logical assumption here. Can def >> be expressed differently?
3. Obviously Codec isn't a monad. Does def >> has anything to do with monadic composition?

[sergei-shabanau]

Superseded by #65