clojure.zip needs to be rewritten IMO. It's written in more of a scheme
style using vectors. Since then protocols have come out and there's no
reason why this can't make use of those. And yes, at the same time new
functions could probably be added.
I've threatened to re-write this lib several times, and always gotten
pulled away into other projects. Code it up though and I'd love to see it
pushed through.
The first thing that would need to happen would be for the library to get
much better testing, right now there aren't any tests around this lib at
all.
Anyway, that's my 2 cents.
Timothy
On Thu, Jan 2, 2014 at 5:07 AM, Alex Dowad <alexinbeij...@gmail.com> wrote:
> Hi, everybody,
>
> I'm just throwing this out to see if the Clojure core team agrees, and if
> they would like me to code something up and send a PR.
>
> clojure.zip works great if you want to walk a tree and add nodes here and
> there -- append-child, insert-child, insert-left, and insert-right cover
> all the important use cases. If you want to walk a tree and filter nodes
> out, remove has you covered. I've discovered, though, that trying to *move*
> nodes is very cumbersome, far more than it needs to be.
>
> The crux of the problem is here (to quote the API docs):
>
> removefunction
>
> Usage: (remove loc)
>
> Removes the node at loc, returning the loc that would have preceded
> it in a depth-first walk.
>
>
> The problem is that remove "returns the loc that would have preceded" the
> removed node "in a depth-first walk". If I want to push a node down below its
> left/right sibling, or pull it up to become a sibling of its parent, or make
> it swap places with its left/right sibling, etc. etc., going to "the loc that
> would have preceded it in a depth-first walk" is useless. Once the node is
> removed, it's very hard to find my way back to the loc where I want to insert
> it.
>
>
> I'm not saying that the API for remove is faulty -- it's perfect if your goal
> is just to filter nodes out. But functions are needed which can remove a node
> *and* return the loc above/to the left/to the right.
>
>
> When I ran into this problem, I cracked open the source for clojure.zip,
> looked at the source for "remove", and coded this variant up:
>
>
> (defn remove-and-up [loc]
> (let [[node {l :l, ppath :ppath, pnodes :pnodes, rs :r, :as path}] loc]
> (if (nil? path)
> (throw (new Exception "Remove at top"))
> (if (pos? (count l))
> (up (with-meta [(peek l)
> (assoc path :l (pop l) :changed? true)]
> (meta loc)))
> (with-meta [(make-node loc (peek pnodes) rs)
> (and ppath (assoc ppath :changed? true))]
> (meta loc))))))
>
>
> That removes a node, and returns the loc of its parent. My problem is now
> solved. But to a newbie programmer, that problem would have probably been
> insurmountable.
>
>
> What do you think? Is adding a function or two to clojure.zip warranted?
>
>
> Thanks, AD
>
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