I'm not 100% happy with this plus it doesn't really answer the original
question, but in case it helps in some way ...
Recently, I had a record I was working on that holds a seq that could be a
lazy infinite seq that I ended up using this as the major part of
print-method implementation:
(def ^:dynamic *print-look-ahead-length* 2)
(defn seq->str
[s]
(let [[f' r] (split-at *print-look-ahead-length* s)
f (apply list f')]
(if (seq r)
(str "(" (first f) " " (second f) " <+ more>)")
(str f))))
I played with checking for instance of a number of things that just got too
messy for me at the time. So, for now, I just decided it was good enough to
basically see 2 items into the seq and indicate if there are more. This
could easily be made more variable in places.
Bret
On Monday, November 2, 2020 at 7:23:08 PM UTC-6 Austin Haas wrote:
>
> Thanks, Justin!
>
> Yeah, I noticed that range doesn't return an instance of
> clojure.lang.LazySeq, so I added a print-method for clojure.lang.Iterate.
> And that one seems to work as expected, but apparently you can't override
> the print-method for clojure.lang.LazySeq.
>
> But this doesn't seem like a good approach, anyway, because I don't want
> to change the printing behavior globally.
>
> I think I'm just going to have to forego logging arbitrary things, and
> maybe implement some optional santization if necessary.
> On Monday, November 2, 2020 at 12:40:48 PM UTC-8 [email protected] wrote:
>
>> hit send too soon --
>>
>> also, that print-method doesn't catch all lazy values
>>
>> user=> (instance? clojure.lang.LazySeq (range))
>> false
>>
>> user=> (supers (class (range)))
>> #{java.lang.Iterable java.util.List clojure.lang.Obj
>> clojure.lang.IPending java.io.Serializable clojure.lang.IHashEq
>> java.util.Collection clojure.lang.IObj clojure.lang.Sequential
>> clojure.lang.Seqable clojure.lang.IPersistentCollection
>> clojure.lang.ASeq clojure.lang.IReduce java.lang.Object
>> clojure.lang.ISeq clojure.lang.IMeta clojure.lang.IReduceInit}
>>
>> On Mon, Nov 2, 2020 at 12:36 PM Justin Smith <[email protected]> wrote:
>> >
>> > > The next step might be to investigate why infinite lazy seqs don't
>> print as clojure.lang.LazySeq, like the finite ones.
>> >
>> > that printing of "clojure.lang.LazySeq@c5d38b66" relies on completely
>> > realizing the input, as it relies on the hash, which relies on the
>> > fully realized value
>> >
>> > On Mon, Nov 2, 2020 at 12:32 PM Austin Haas <[email protected]>
>> wrote:
>> > >
>> > > Thanks, Juan.
>> > >
>> > > I don't need to know the length of the seq, though, only that it is
>> lazy. I don't want to realize any lazy seqs. Ideally, I'd like to be able
>> to print any data structure and have all lazy seqs print just like it does
>> in the example I gave above (i.e., "clojure.lang.LazySeq@c5d38b66"),
>> whether it is finite or infinite.
>> > >
>> > > I also don't want to walk through every data structure to check if it
>> contains a lazy seq, but maybe that is the only option.
>> > >
>> > > I've also tried:
>> > >
>> > > (defmethod print-method clojure.lang.LazySeq [q, w]
>> > > (.write w "#clojure.lang.LazySeq"))
>> > >
>> > > The next step might be to investigate why infinite lazy seqs don't
>> print as clojure.lang.LazySeq, like the finite ones.
>> > > On Monday, November 2, 2020 at 9:22:58 AM UTC-8 [email protected]
>> wrote:
>> > >>
>> > >> Hi Austin,
>> > >>
>> > >> Since there is no way to know the length of a lazy-seq without
>> realizing it, I think your only choice is to set a limit on it by binding
>> *print-length* if you are not sure about the sequence.
>> > >>
>> > >> Other thing you can try is bounded-count like this :
>> > >>
>> > >> (defn looks-finite? [xs]
>> > >> (let [limit 1000]
>> > >> (< (bounded-count limit xs) limit)))
>> > >>
>> > >> (looks-finite? (map inc (range))) ;; => false
>> > >> (looks-finite? (map inc (range 100))) ;; => true
>> > >>
>> > >> I hope that helps.
>> > >>
>> > >> Juan
>> > >> El domingo, 1 de noviembre de 2020 a las 20:06:39 UTC-3, Austin Haas
>> escribió:
>> > >>>
>> > >>>
>> > >>> How can I make sure that a logging function won't try to realize an
>> infinite lazy seq that could be anywhere in the arguments passed to the
>> logging function?
>> > >>>
>> > >>> Is there some way to guarantee that lazy seqs won't be realized
>> when converting to a string?
>> > >>>
>> > >>> I know I can bind *print-length*, but I don't want to constrain
>> every collection.
>> > >>>
>> > >>> And I know that lazy seqs aren't always realized, but that doesn't
>> seem to help if they are infinite:
>> > >>>
>> > >>> user=> (str (map inc (range 10)))
>> > >>> "clojure.lang.LazySeq@c5d38b66"
>> > >>>
>> > >>> user=> (str (map inc (range)))
>> > >>> <never ends>
>> > >>>
>> > >>> Thanks.
>> > >>>
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>>
>>
>
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