On Jun 14, 6:37 am, Wrexsoul <d2387...@bsnow.net> wrote:
> On Jun 13, 11:07 pm, James Reeves <weavejes...@googlemail.com> wrote:
>
> > For instance, lets say I want to return a lazy list of all the lines
> > in all the files in a directory tree:
>
> > (use '(clojure.contrib java-utils
> > duck-streams))
>
> When clojure.contrib releases version 1.0, that might be an option.
>
Most interesting Clojure projects already depend on contrib in some
form. You will need it eventually :)
And frankly, the main reason there is not a 1.0 of contrib yet is that
no-one has bothered to tag one. :P
> > (defn all-line-seq [dir]
> > (mapcat read-lines (file-seq (file dir))))
>
> > Since file-seq, read-lines and mapcat all lazy, my final result is
> > lazy as well.
>
> Seems to me that unless you completely consume the sequence, it will
> leak a file handle.
That's a problem with lazy seqs and IO in general. You just need to be
careful.
IIRC Rich is working on a solution, though.
> > > Is file-seq recursive? I'd figured it just returned the flat contents
> > > of a directory.
>
> > Yep, it's recursive.
>
> OK. Even so, the implementation in terms of super-lazy-seq shows the
> power of that macro. Mostly, I'm doing quite a few things with I/O
> that require custom next-item-in-seq generators for the records or
> other objects returned, for which it's coming in real handy. In those
> circumstances lazy-seq saves the bother of doing a loop/recur in
> everyplace that consumes some records, and super-lazy-seq in turn lets
> me still use a loop/recur style in the one place where the code
> extracts and grovels over the records one by one.
Maybe I'm just thick, but why would you want to use loop/recur style
when the following works:
(defn items-from-stateful-source [src]
(when-let [item (take-item src)] ; take-item returns nil when there
are no more items
(lazy-seq (cons item (items-from-stateful-source src)))))
Maybe I'm just too infatuated with higher-order functions and
recursion. looping constructs are boring :)
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