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)
Installation
Fipp artifacts are published on Clojars.
To depend on this version with Lein, add the following to your project.clj
:
[fipp "0.6.15"]
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. There are several known issues on both the Fipp and CLJS sides that are in the process of being fixed. While I wouldn't yet trust Fipp to serialize CLJS data durably, it should be more than usable interactively. Please let me know if it isn't for you.
Colorization & REPL Integration
Puget uses Fipp's engine to provide an alternative, colorizing printer.
Whidbey integrates Puget in to nREPL via Leinigen, 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 to70
.:print-length
behaves as and defaults toclojure.core/*print-length*
.:print-level
behaves as and defaults toclojure.core/*print-level*
.:print-meta
behaves as and defaults toclojure.core/*print-meta*
.
Any other supported/hidden options are subject to change.
Conveniences
The dbg
macro can be used for convenient "printf debugging" of
source file, line, expression, and evaluation result to *err*
.
(require '[fipp.edn :refer [dbg]])
(dbg (repeat 5 (range 10)))
This will print:
/path/to/that/file.clj:2
(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 clojure.repl/pst
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 (Compiler.java:6927)
clojure.lang.Compiler.eval (Compiler.java:6890)
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)
Fast!
In my non-scientific testing, it has proven to be at least five times as fast
as clojure.pprint
. 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 yield
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.
Idiomatic!
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/primitives.md for details.
License
Copyright © 2015 Brandon Bloom
Distributed under the Eclipse Public License, the same as Clojure.
Acknowledgements
Fipp is fast in part thanks to YourKit's Java Profiler.