Hashp is a better prn for debugging Clojure code. Inspired by projects like Spyscope, Hashp (ab)uses data readers to make it easier to get useful debugging data sent to STDERR.

Once installed, you can add #p in front of any form you wish to print:

(ns example.core)
(defn mean [xs]
  (/ (double #p (reduce + xs)) #p (count xs)))

It's faster to type than (prn ...), returns the original result, and produces more useful output by printing the original form, function and line number:

user=> (mean [1 4 5 2])
#p[example.core/mean:4] (reduce + xs) ⇒ 12
#p[example.core/mean:4] (count xs) ⇒ 4
3.0

To use #p in a tools.deps project, add the following dependency to your project's deps.edn file:

{:deps {dev.weavejester/hashp {:mvn/version "0.5.1"}}}

You will then need to install hashp before any other file is loaded.

((requiring-resolve 'hashp.install/install!))

To make #p globally available to all Leiningen projects, add the following to ~/.lein/profiles.clj:

{:user
 {:dependencies [[dev.weavejester/hashp "0.5.1"]]
  :injections [((requiring-resolve 'hashp.install/install!))]}}

To make #p globally available to all Boot projects, add the following to ~/.boot/profile.boot:

(set-env! :dependencies #(conj % '[dev.weavejester/hashp "0.5.1"]))
((requiring-resolve 'hashp.install/install!))
(boot.core/load-data-readers!)

The hashp.install/install! function may be given named options:

(require 'hashp.install)
(hashp.install/install :color? false)

There are several options supported:

• :color? - set to true if the output should be in color. Defaults to true unless the NO_COLOR environment variable was set.

• :disabled? - if true then #p will do exactly nothing. This is useful if you want to disable #p in a production environment with no loss of performance. Defaults to false.

• :tag - a symbol used for the tag, defaults to 'p.

• :template - a string that can be used to customize the format of #p. Defaults to: "#{tag}[{ns}/{fn}:{line}] {form} ⇒ {value}

• :writer - a Writer to use for the output, defaults to *err*, which writes to STDERR. If you want to write to STDOUT instead, set this to *out*.

Copyright © 2025 James Reeves

Released under the MIT license.