enhance pprint to print type for defrecord (as in pr)

Question

pprint currently doesn't print the names of defrecord types, instead printing just the underlying map. This is in contrast to pr-str/println. This ticket proposes that the behaviour of pprint is changed to match pr-str and println's.

More discussion at https://groups.google.com/forum/#!topic/clojure-dev/lRDG6a5eE-s


user=> (defrecord myrec [a b])
user.myrec
user=> (->myrec 1 2)
#user.myrec{:a 1, :b 2}
user=> (pr-str (->myrec 1 2))
"#user.myrec{:a 1, :b 2}"
user=> (println (->myrec 1 2))
#user.myrec{:a 1, :b 2}
nil
user=> (pprint (->myrec 1 2))
{:a 1, :b 2}
nil


*Approach:* Add new IRecord case to pprint's simple-dispatch mode. Extract guts of pprint-map to pprint-map-kvs and call it from both existing pprint-map and new pprint-record. Set multimethod preference for IRecord version. Added test.


user=> (pprint (->myrec 1 2))
#user.myrec{:a 1, :b 2}

*Patch:* CLJ-1890-pprint-records-2.patch

*Prescreened by:* Alex Miller

*Also see:* CLJS-1753

Answer 1

Comment made by: desk@danielcompton.net

The fix for this will needed to be ported to ClojureScript too.

Answer 2

Comment made by: steveminer@gmail.com

Added patch to pprint records with classname.

Answer 3

Comment made by: steveminer@gmail.com

Open question: How should pprint handle a record that has a print-method defined for it? Should the print-method be used instead of the pprint default?

The current release and my patch do not consider the print-method when calling pprint.

Answer 4

_Comment made by: alexmiller_

I do not think pprint should check for or use print-method. pprint has it's own simple-dispatch multimethod that you can extend, or it will ultimately fall through to pr (which can be extended via print-dup).

Example of the former:


user=> (defrecord R [a])
user=> (def r (->R 1))
user=> (pprint r)
{:a 1}

user=> (use 'clojure.pprint)
user=> (defmethod simple-dispatch user.R [r] (pr r))
#object[clojure.lang.MultiFn 0x497470ed "clojure.lang.MultiFn@497470ed"]
user=> (pprint r)
#user.R{:a 1}

Answer 5

Comment made by: steveminer@gmail.com

Right, clojure.pprint/simple-dispatch is there for user code to customize pprint, independent of whatever they might do with print-method. No need to conflate the two. So the patch is ready to review.

Answer 6

Comment made by: michaelblume

Patch does not appear to apply cleanly to current master.

Answer 7

Comment made by: michaelblume

Doesn't apply cleanly to any of the beta tags, does apply cleanly to 1.8.0, but can't rebase without a conflict. Steve, you should probably fix that.

Answer 8

Comment made by: steveminer@gmail.com

revised patch for current master (Clojure 1.9 beta4)

Answer 9

Comment made by: steveminer@gmail.com

The old patch was prescreened but I guess the new patch should be reconsidered from scratch as namespaced maps were added to Clojure in between patches. By the way, I don't think there are any tests to cover pretty-printing namespaced maps. The only test I could find was for pr-str of a namespaced map. In any case, I tried to make sure the prefix logic was maintained so it should still work. The same test for pretty-printing records is used in both versions of the patch.

Answer 10

Reference: https://clojure.atlassian.net/browse/CLJ-1890 (reported by desk@danielcompton.net)