[Haskell-cafe] A home-brew iteration-alike library: some extension quiestions

[Permjacov Evgeniy]

Well, It looks like with 'transformer' look onto iteratees it is
possible to fold two streams without anything except Iteratee, yet some
complications arise. Even real zipping. for example merging two sorted
streams with output stream sorted, is expressible. More preciesely, I
tried to write a separate module (attached) and with careful use of
'runners' I got stack of Iteratee/Enumeratee transformers, that shall do
the job. However, typing of the running function and input streams is a
mess:

t \i e g -> mkEnumeration $ enumerateTo g $ mkIteration $ enumerateTo e
(mkIteration i)
\i e g -> mkEnumeration $ enumerateTo g $ mkIteration $ enumerateTo e
(mkIteration i)
  :: Iteratee e2 a s2 (Iteratee e1 a s1 (Enumeratee e r s m)) a
     -> Enumeration e2 a s2 (Iteratee e1 a s1 (Enumeratee e r s m))
     -> Enumeration e1 a s1 (Enumeratee e r s m)
     -> Enumeration e r s m

And lifting of innermost iteratee's 'nextIM' is not sufficient for merge
of sorting streams: A separate one must be written.
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