Hashp

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.

Usage

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

Installation

tools.deps

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 "0.4.0"}}}

You will then need to load the hashp.core namespace before using #p:

(require 'hashp.preload)

Leiningen

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

{:user
 {:dependencies [[dev.weavejester/hashp "0.4.0"]]
  :injections [(require 'hashp.preload)]}}

Boot

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

(set-env! :dependencies #(conj % '[dev.weavejester/hashp "0.4.0"]))
(require 'hashp.preload)
(boot.core/load-data-readers!)

Configuration

Hashp can be turned on or off via the hashp.config/*disable-hashp* var. This is checked when #p is initially evaluated, so if it is changed, any existing namespace that uses #p will need to be reloaded before the change takes effect.

user=> (alter-var-root #'hashp.config/*disable-hashp* (constantly true))
true
user=> (require 'example.core :reload)
nil
user=> (mean [1 4 5 2])
3.0

You can also turn the colors off. Hashp respects the NO_COLOR environment variable, and you can also set it via the hashp.config/*disable-color* var. Unlike *disable-hashp*, this is checked on each print, so there's no need to reload the namespaces.

user=> (alter-var-root #'hashp.config/*disable-color* (constantly true))
true

Finally, you can change the output writer. By default this is *err*, which outputs to STDOUT, but you can set this to any other print writer, such as *out*.

user=> (alter-var-root #'hashp.config/*hashp-output* (constantly *out*))
#object[java.io.PrintWriter 0x2deddab6 "java.io.PrintWriter@2deddab6"]

License

Copyright © 2025 James Reeves

Released under the MIT license.