Re: [PATCH] Gnu Elpa: stream.el: Add some more basic stream operations

[Michael Heerdegen]

Yuri Khan <address@hidden> writes:

> > Would it make sense to add an `seq-take-until' for convenience?
>
> seq-take-until might be a fitting addition to seq-take-while.
> seq-drop-until, for completeness?

Hmm, isn't `seq-drop-until' redundant - because it's the same as
`seq-drop-while' with negated predicate?

For example, if stream

  S = 0, 0, ..., 0, 1, 2, 3, ...

then naturally would

  (seq-drop-while #'zerop S) == 1, 2, ...
                             == (seq-drop-until
                                  (lambda (n) (not (zerop n)))
                                   S)

`seq-take-until' is obviously not redundant in the same way.  So, why is
the symmetry broken?  I think the problem is the wording:
`seq-drop-until' is simply not the natural counterpart of
`seq-drop-while'.

We would want a function seq-X so that

  (seq-X #'zerop S) == 0, 1, 2, ...

I think that this function would be useful (I already needed it).  But
what word sequence X would describe these semantics (how should we call
the function)?


Michael.