Hi,
I am writing to ask if a behavior that I find strange is a bug or
intended? In the latter case I would like to learn why is it so.
In the REPL I see the following, that I think is OK:
user=> (def test-data (lazy-seq [(str ["ZiZi"])]))
#'user/test-data
user=> test-data
("[\"ZiZi\"]")
However, if I call "print" in between the previous 2 lines, test-data
becomes different at the end:
user=> (def test-data (lazy-seq [(str ["ZiZi"])]))
#'user/test-data
user=> (print test-data)
([ZiZi])nil
user=> test-data
("[ZiZi]")
I found that the "binding" of *print-readably* in the code of "print"
makes the difference. If it is nil (as in print), I get the faulty
value. If it is true, then I get the right (inner-quoted) value.
I learned (from e.g. Stuart Halloway at
http://grokbase.com/t/gg/clojure/149d3t0gwh/schrodingers-cat-in-clojure)
that mixing lazy evaluation and I/O can lead to confusing situations and
that is normal. However here I feel that I get different values of the
same expression depending on which action triggers its realization: if
it is (e.g.) print, then it is realized in a faulty way: "[ZiZi]" is not
correct, since ZiZi should be quoted inside the string by \"-s. (I know
the missing inner quotes are not just a REPL printing issue as I
distilled this question after spending hours to hunt down strange error
messages in a real commercial program.) In other words it seems to me
that having *print-readably* nil, makes the realization of this lazy-seq
failing.
I also see that the problem disappears if I do not use lazy-seq (or
map...) or if I code the string directly (without "str"):
user=> (def test-data (lazy-seq ["[\"ZiZi\"]"]))
#'user/test-data
user=> (print test-data)
(["ZiZi"])nil
user=> test-data
("[\"ZiZi\"]")
and
user=> (def test-data [(str ["ZiZi"])])
#'user/test-data
user=> (print test-data)
[["ZiZi"]]nil
user=> test-data
["[\"ZiZi\"]"]
I verified this behavior both in (pure, i.e. not Lein) REPL of Clojure
1.8 and 1.9.0-alpha20.
Please help me understanding what's going on here.
Thanks,P
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