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Fast Idiomatic Pretty Printer for Clojure

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Fast Idiomatic Pretty-Printer

Fipp is a better pretty printer for Clojure and ClojureScript.

Like clojure.pprint, this pretty printer has a linear runtime and uses bounded space. However, unlike clojure.pprint, Fipp's implementation is tuned for great performance and has a functional, data-driven API.

The data interface is agnostic to the source language. Printers are included for Edn data and Clojure code, but it is easy to create a pretty printer for your own language or documents: Even if they're not made out of Clojure data!

Fipp is great for printing large data files and debugging macros, but it is not suitable as a code reformatting tool. (explanation)


Fipp artifacts are published on Clojars.

To depend on this version with Lein, add the following to your

[fipp "0.6.24"]

This version of Fipp works with Clojure 1.7 or newer.

See the v0.5 branch for a version of Fipp that works with Clojure 1.6.

ClojureScript is supported from build 3269 and up.

Colorization & REPL Integration

Puget uses Fipp's engine to provide an alternative, colorizing printer.

Whidbey integrates Puget in to nREPL via Leiningen, so that every evaluation pretty prints in color.

Printer Usage

;; Refer with a rename to avoid collision with your REPL's pprint.
(require '[fipp.edn :refer [pprint] :rename {pprint fipp}])

(fipp [1 2 3]) (fipp (range 50)) (fipp (range 20)) (fipp (range 20) {:width 10})

(require '[fipp.clojure]) (fipp.clojure/pprint '(let [foo "abc 123" bar {:x 1 :y 2 :z 3}] (do-stuff foo (assoc bar :w 4))) {:width 40})

The available options are:

  • :width
    defaults to
  • :writer
    defaults to
    (Clojure only).
  • :print-fn
    defaults to
    (ClojureScript only).
  • :print-length
    behaves as and defaults to
  • :print-level
    behaves as and defaults to
  • :print-meta
    behaves as and defaults to

Any other supported/hidden options are subject to change.



macro can be used for convenient "printf debugging" of source file, line, expression, and evaluation result to
(require '[fipp.edn :refer [dbg]])
(dbg (repeat 5 (range 10)))

This will print:

(repeat 5 (range 10))
((0 1 2 3 4 5 6 7 8 9)
 (0 1 2 3 4 5 6 7 8 9)
 (0 1 2 3 4 5 6 7 8 9)
 (0 1 2 3 4 5 6 7 8 9)
 (0 1 2 3 4 5 6 7 8 9))

A Fipp-enabled version of

is also available:
user=> (require '[fipp.repl :refer [pst]])
user=> (throw (ex-info "whoops" {:xs (range 20) :ys (range 20)}))

ExceptionInfo whoops clojure.core/ex-info (core.clj:4617) user=> (fipp.repl/pst) ExceptionInfo whoops {:xs (0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19), :ys (0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19)} clojure.core/ex-info (core.clj:4617) clojure.core/ex-info (core.clj:4617) user/eval3185 (form-init1248204588518004004.clj:1) user/eval3185 (form-init1248204588518004004.clj:1) clojure.lang.Compiler.eval ( clojure.lang.Compiler.eval ( clojure.core/eval (core.clj:3105) clojure.core/eval (core.clj:3101) clojure.main/repl/read-eval-print--7408/fn--7411 (main.clj:240) clojure.main/repl/read-eval-print--7408 (main.clj:240) clojure.main/repl/fn--7417 (main.clj:258) clojure.main/repl (main.clj:258)


In my non-scientific testing, it has proven to be at least five times as fast as

. It also has the nice property of printing no later than having consumed the bounded amount of memory, so you see your first few lines of output instantaneously.

The core algorithm is described by Swierstra and Chitil in Linear, Bounded, Functional Pretty-Printing.

Swierstra and Chitil's implementation uses lazy evaluation and requires tying the knot to interleave the measuring and printing phases to achieve the bounded space goal.

However, this implementation is instead a port of the strict evaluation strategy as described by Kiselyov, Peyton-Jones, and Sabry in Lazy v. Yield: Incremental, Linear Pretty-printing.

Clojure's transducers are used to simulate generators and their

operator. Unlike lazy reduction, transducers interleave execution of multi-phase transformations by function composition. This enables preservation of the bounded-space requirement and eases reasoning about the program's behavior. Additionally, it avoids a lot of intermediate object allocation.


Clojure's included pretty printer supports pluggable dispatch tables and provides an API for controlling the printing process. The programming model is side-effectual. For example, to print a breaking newline, you execute

(pprint-newline :linear)
. This means that it's a difficult and tricky process to write or compose new pretty printers.

Fipp, on the other hand, accepts a "pretty print document" as input. This document is similar to HTML markup using hiccup.

Here are some examples:

(require '[fipp.engine :refer (pprint-document)])

(defn ppd [doc] (pprint-document doc {:width 10}))

(ppd [:span "One" :line "Two" :line "Three"])

(ppd [:group "(do" [:nest 2 :line "(step-1)" :line "(step-2)"] ")"])

If you want to write your own printer, see doc/ for details.


Copyright © 2015-2021 Brandon Bloom

Distributed under the Eclipse Public License, the same as Clojure.


Fipp is fast in part thanks to YourKit's Java Profiler.

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