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clojure

How can I set the default number format in Clojure?

I'm working with Clojure on some binary formats in which it makes sense to inspect numbers that are hex formatted (0x10). How can I configure Clojure to render numbers as hex, by default? This is probably most relevant to me while in a REPL, but I'm also interested in more general mechanisms.

Solution

  • Clojure uses to multi-methods for printing data: print-method (intended to provide output to be read by humans) and print-dup (that produces output that can be parsed with read).

    Thus for REPL you can simply provide your implementation of print-method for java.lang.Numbers like in the REPL session below:

    123
=> 123

(prn 123)
123
=> 123

(defmethod print-method Number
  [n ^java.io.Writer w]
  (.write w (format "0x%X" n)))
=> #object[clojure.lang.MultiFn 0x52ad430a "clojure.lang.MultiFn@52ad430a"]

123
=> 0x7B

(prn 123)
0x7B
=> nil