Puget

Puget is a Clojure library for printing Clojure and EDN values. Under the hood, Puget formats data into print documents and uses fipp to render them.

Puget offers several features which set it apart from FIPP and Clojure's native pretty-printing functions. Syntax coloring is the most widely used, followed by canonical printing. Custom value rendering is supported using type dispatch to select print handlers.

Installation

Puget releases are published on Clojars. To use the latest version with Leiningen, add the following dependency to your project definition:

See Whidbey for nREPL and Leiningen integration.

Usage

Puget's printing is controlled by a map of options which configure things like print width, sorting mode, color scheme and style, whether to print metadata, and so on. The default options are held in the dynamic var puget.printer/*options*, which can be bound using with-options. See the puget.printer namespace documentation for the full set of options.

These options are used to construct a printer to render values with. pprint and pprint-str will automatically create a PrettyPrinter record from the current and passed options, or you can use pretty-printer or canonical-printer to construct one manually. render-out and render-str take a printer and a value if you need maximum control over the printing.

Syntax Coloring

Puget's first major feature is colorizing the printed data by rendering it with embedded markup. Different syntax elements are given different colors to make the printed output much easier for humans to parse. This is similar to syntax highlighting, but much easier since the code works directly with the data instead of parsing it from text!

Elements are mapped to color codes by the :color-scheme option. The :print-color option can be set to enable colorization using the with-color macro - alternately, the cprint function always prints with colored output enabled.

Puget supports three different kinds of color markup:

• :ansi (the default) adds ANSI color escapes for terminal outputs.
• :html-inline adds HTML span elements with inline style attributes.
• :html-classes adds span elements with semantic class attributes.

See the puget.color.ansi namespace for the available ANSI color styles which can be applied to syntax elements.

Canonical Representation

Puget also provides canonical serialization of data. In most cases, if two data values are equal, they should be printed identically. This is important for when the printed data is hashed, but it also makes it easier to process maps and other structures with similar contents.

Puget uses the arrangement library to sort the values in sets and the keys in maps so they are always printed the same way. This can be disabled with the :sort-keys option, or enabled only for collections under a certain size.

Most printing is done with the PrettyPrinter class, but the library also offers the CanonicalPrinter for serializing data in a stricter (and more compact) fashion.

=> (require '[puget.printer :as puget])

=> (puget/pprint #{'x :a :z 3 1.0})
#{1.0 3 :a :z x}

=> (def usd (java.util.Currency/getInstance "USD"))
#'user/usd

=> (puget/pprint usd)
nil

=> (puget/render-out (puget/canonical-printer) usd)
; IllegalArgumentException: No defined representation for class java.util.Currency: USD

Type Extensions

All of Clojure's primitive types are given their standard print representations. To handle non-standard data types, Puget supports a mechanism to dispatch to custom print handlers. These take precedence over the normal rendering mechanisms.

This can be used to provide an EDN tagged-literal representation for certain types, or just avoid trying to pretty-print types which the engine struggles with (such as Datomic database values).

Before rendering a value, the printer checks for a :print-handlers function. If available, it is called with the type of the value to be printed. If the lookup returns a handler, that function is called with the value and the result is used as the rendered format of the value.

The puget.dispatch namespace has functions to help build handler lookup functions. The inheritance-lookup constructor provides semantics similar to Clojure's multimethod dispatch.

As an example, extending #inst formatting to clj-time's DateTime:

=> (require '[clj-time.core :as t]
            '[clj-time.format :as f])

=> (puget/pprint (t/now))
nil

=> (def time-handlers
     {org.joda.time.DateTime
      (puget/tagged-handler
        'inst
        (partial f/unparse (f/formatters :date-time)))})
#'user/time-handlers

=> (puget/pprint (t/now) {:print-handlers time-handlers})
#inst "2014-05-14T01:05:53.885Z"

If no handler is specified for a given type and it's not a built-in EDN type, Puget refers to the :print-fallback option, which must be one of:

• :pretty (the default) prints a colored representation of the unknown value (not valid EDN!).
• :print falls back to the standard pr-str representation.
• :error throws an exception for types with no defined representation.
• A function which will be called with the printer and the unknown value to render, returning the formatted value.

License

This is free and unencumbered software released into the public domain. See the UNLICENSE file for more information.