Pretty-printed recording using a custom method in Clojure

Question

In Clojure 1.5.0, how can I provide my own pretty-printer for my own record type, defined with defrecord.

(defrecord MyRecord [ab]) (defmethod print-method MyRecord [x ^java.io.Writer writer] (print-method (:ax) writer)) (defmethod print-dup MyRecord [x ^java.io.Writer writer] (print-dup (:ax) writer)) (println (MyRecord. 'a 'b)) ;; a -- OK (clojure.pprint/pprint (MyRecord. 'a 'b)) ;; {:aa, :bb} -- not OK, I want a 

I would like clojure.pprint/pprint also use my cutsom printer (which should now just print beautifully everything that is in field a record for illustrative purposes).

Answer 1

clojure.pprint namespace uses a different send mechanism, and then the clojure.core print clojure.core . You need to use with-pprint-dispatch to configure pprint.

 (clojure.pprint/with-pprint-dispatch print ;;Make the dispatch to your print function (clojure.pprint/pprint (MyRecord. 'a 'b))) 

To set up a simple dispatcher, add something like:

 (. clojure.pprint/simple-dispatch addMethod MyRecord pprint-myrecord) 

Answer 2

Maybe not perfect, but I have not found better than pr and pr-str .

Example REPL session:

  (ns my-ns) (defprotocol Foo (bazfn [this])) (defrecord Bar [a] Foo (bazfn [this] 123)) (pr-str (Bar. "ok")) ;;=> "#my_ns.Bar{:a \"ok\"}" (pr (Bar. "ok")) ;; prints the same as above 

Answer 3

It was very confusing, with the right answers to different parts of the problem, common in different places, so I put it all together in the hope that someone could save some time.

I went through all the permutations of the definition method print-method , print-dup and simple-dispatch for defrecord and set the dynamic vars *print-pprint-dispatch* and *print-dup* . I set the defrecord example via pr and pprint and came up with the following flowchart. Now it makes sense to see everything at once.

A permutation code is brute force; I just looked at the exits and directly created a Visio diagram. Nothing unusual.

 (ns print-test (:require [clojure.pprint :as pp])) (defrecord tr000 [val]) (defrecord tr001 [val]) (defrecord tr010 [val]) (defrecord tr011 [val]) (defrecord tr100 [val]) (defrecord tr101 [val]) (defrecord tr110 [val]) (defrecord tr111 [val]) ;;(defmethod print-method tr000 [obj writer] (.write writer "tr000 print-method")) ;;(defmethod print-dup tr000 [obj writer] (.write writer "tr000 print-dup")) ;;(defmethod pp/simple-dispatch tr000 [obj] (.write *out* "tr000 simple-dispatch")) ;;(defmethod print-method tr001 [obj writer] (.write writer "tr001 print-method")) ;;(defmethod print-dup tr001 [obj writer] (.write writer "tr001 print-dup")) (defmethod pp/simple-dispatch tr001 [obj] (.write *out* "tr001 simple-dispatch")) ;;(defmethod print-method tr010 [obj writer] (.write writer "tr010 print-method")) (defmethod print-dup tr010 [obj writer] (.write writer "tr010 print-dup")) ;;(defmethod pp/simple-dispatch tr010 [obj] (.write *out* "tr010 simple-dispatch")) ;;(defmethod print-method tr011 [obj writer] (.write writer "tr011 print-method")) (defmethod print-dup tr011 [obj writer] (.write writer "tr011 print-dup")) (defmethod pp/simple-dispatch tr011 [obj] (.write *out* "tr011 simple-dispatch")) (defmethod print-method tr100 [obj writer] (.write writer "tr100 print-method")) ;;(defmethod print-dup tr100 [obj writer] (.write writer "tr100 print-dup")) ;;(defmethod pp/simple-dispatch tr100 [obj] (.write *out* "tr100 simple-dispatch")) (defmethod print-method tr101 [obj writer] (.write writer "tr101 print-method")) ;;(defmethod print-dup tr101 [obj writer] (.write writer "tr101 print-dup")) (defmethod pp/simple-dispatch tr101 [obj] (.write *out* "tr101 simple-dispatch")) (defmethod print-method tr110 [obj writer] (.write writer "tr110 print-method")) (defmethod print-dup tr110 [obj writer] (.write writer "tr110 print-dup")) ;;(defmethod pp/simple-dispatch tr110 [obj] (.write *out* "tr110 simple-dispatch")) (defmethod print-method tr111 [obj writer] (.write writer "tr111 print-method")) (defmethod print-dup tr111 [obj writer] (.write writer "tr111 print-dup")) (defmethod pp/simple-dispatch tr111 [obj] (.write *out* "tr111 simple-dispatch")) (def t000 (->tr000 10)) (def t001 (->tr001 20)) (def t010 (->tr010 30)) (def t011 (->tr011 40)) (def t100 (->tr100 50)) (def t101 (->tr101 60)) (def t110 (->tr110 70)) (def t111 (->tr111 80)) (def recs [t000 t001 t010 t011 t100 t101 t110 t111]) (def dt (java.time.LocalTime/now)) (defmethod print-dup java.time.LocalTime [obj writer] (.write writer "datetime_dup")) (println "(pr ...) outputs the following") (doseq [rec recs] (doseq [prppd [nil #(.write *out* "pprint-dispatch with" %)]] (binding [pp/*print-pprint-dispatch* (if prppd #(.write *out* (str "pprint-dipatch-with" %)) pp/*print-pprint-dispatch*)] (doseq [pd [false true]] (binding [*print-dup* pd] (let [ppdstr (format "%6s" (boolean pp/*print-pprint-dispatch*)) dupstr (format "%6s" *print-dup*) outstr (pr-str rec)] (binding [*print-dup* false] (println ppdstr dupstr ":" outstr)))))))) (println "\n(pprint ...) outputs the following") (doseq [rec recs] (doseq [prppd [false true]] (binding [pp/*print-pprint-dispatch* (if prppd #(.write *out* (str "pprint-dipatch-with" %)) pp/*print-pprint-dispatch*)] (doseq [pd [false true]] (binding [*print-dup* pd] (let [outstr (with-out-str (pp/pprint {:ppdstr prppd :dupstr pd :dt dt :strobj rec}))] (binding [*print-dup* false] (println outstr "\n"))))))))