print-method is inconsistent with regard to clojure.pprint with print-level

Thu, 28 Sep 2023 07:02:04 +0000

Repro:

;; print-method

user=> (binding [*print-level* 1]
         (prn {:a 1 :b 2}))
{:a 1, :b 2}
nil

user=> (binding [*print-level* 1]
         (prn {:a {:b 2}}))
{:a #}
nil

user=> (binding [*print-level* 1]
         (prn [(clojure.lang.MapEntry. :a 1)
               (clojure.lang.MapEntry. :b 2)]))
[# #]
nil

;; clojure.pprint

user=> (binding [*print-level* 1]
         (clojure.pprint/pprint {:a 1 :b 2}))
{#, #}
nil

user=> (binding [*print-level* 1]
         (clojure.pprint/pprint {:a {:b 2}}))
{#}
nil

user=> (binding [*print-level* 1]
         (clojure.pprint/pprint
           [(clojure.lang.MapEntry. :a 1)
            (clojure.lang.MapEntry. :b 1)]))
[# #]
nil

The docstring for *print-level* says:

If an object is a collection and is at a level greater than or equal to the value bound to print-level, the printer prints '#' to represent it.

A map entry is a collection and in {:a 1, :b 2} is at a level equal to *print-level*, so I would expect prn to have the same output as clojure.pprint.

problem with Null exception in cl-format

Wed, 16 Aug 2023 14:36:19 +0000

If the format string ends in ~@, there is code in cl-format to detect this
and issue a format-error. However, that error detection is wrong, and a null exception
happens rather than the format-error being reported.

To reproduce this, simply evaluate the following.

clojure.pprint> (cl-format false "~@")
Execution error (NullPointerException) at nrepl.middleware.interruptible-eval/evaluate$fn$fn (interruptible_eval.clj:87).

I have a fix for this which I'd like to contribute.

Here is the new version of the code compile-directive

(defn- compile-directive [s offset]
  (let [[raw-params [rest offset]] (extract-params s offset)
        [_ [rest offset flags]] (extract-flags rest offset)
        directive (first rest)
        ;; previous version was missing (if directive ...) here thus (format-error ...) never reached
        def (if directive (get directive-table (Character/toUpperCase ^Character directive)))
        params (if def (map-params def (map translate-param raw-params) flags offset))]
    (if (not directive)
      (format-error "Format string ended in the middle of a directive" offset))
    (if (not def)
      (format-error (str "Directive \"" directive "\" is undefined") offset))
    [(struct compiled-directive ((:generator-fn def) params offset) def params offset)
     (let [remainder (subs rest 1) 
           offset (inc offset)
           trim? (and (= \newline (:directive def))
                      (not (:colon params)))
           trim-count (if trim? (prefix-count remainder [\space \tab]) 0)
           remainder (subs remainder trim-count)
           offset (+ offset trim-count)]
       [remainder offset])]))

The old version

Clojure Q&A - Questions without answers in Printing

print-method is inconsistent with regard to clojure.pprint with *print-level*

problem with Null exception in cl-format

print-method is inconsistent with regard to clojure.pprint with print-level