printing and reading date types

Fri, 20 May 2022 05:31:02 +0000

To my understanding, Clojure's pr function prints objects so that when read back will be = to the original object. My main source for this come s from this talk https://youtu.be/pbodL96HM28?t=216 from Clojure core developer Stuart Sierra ( I cannot find any docs to say what guarantees pr offers).

If this is correct, then pr is not working for java.sql.Timestamp and java.util.Calendar. For example, this returns false.

(let [d (java.sql.Timestamp. 1)]
(= d
(read-string
  (pr-str d))))

Further, Clojure's documentation says , print-dup, when true, means that objects will be printed in a way that preserves their type when read in later

This is not the case for java.sql.Timestamp and java.util.Calendar

`
(binding [*print-dup* true]
(prn (java.sql.Timestamp. 1)))
=> #inst "1970-01-01T00:00:00.001000000-00:00"

As well as being interesting to get some answers to the above, understanding these issues might give some basis for Clojure's support of java.time date types as tracked by https://clojure.atlassian.net/browse/CLJ-2224 .

I understand the above behaviour can be changed by users, but I am asking about the default implementations.

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printing and reading date types