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Active Clojure

A library with various basic utilities for programming with Clojure.



The active.clojure.record namespace implements a define-record-type form similar to Scheme's SRFI 9.

Records (Spec)

The active.clojure.record-spec namespace implements a define-record-type form similar to Scheme's SRFI 9 (similar to active.clojure.record).

Additionally, this form creates Clojure Specs according to provided metadata.


(ns your.namespace
  (:require [active.clojure.record-spec :as rs]
            [clojure.spec.alpha :as s]
            [clojure.spec.test.alpha :as stest]
            [clojure.spec.gen.alpha :as gen]))

(s/def ::color #{:hearts :diamonds :spades :clover})
(s/def ::number #{:ace :two :three :four :five :six :seven :eight :nine :ten :jack :queen :king})

(rs/define-record-type card
  (make-card number color) card?
  [^{:spec ::number} number card-number
   (^{:doc "Field with spec, lens and doc." :spec ::color}
   color card-color card-color-lens)])

This defines the following Specs (aside from what the regular active.clojure.records already define):

  • ::card, a Spec which conforms values that are instances of a card (see example below).
  • Specs ::card-number and ::card-color for accessors. Note that these names are not based on the given accessor names but rather a concatenation of the record type and field names.
  • Spec for the constructor function.
(s/explain ::card (make-card :four :spades))
;; => Success!
(s/explain ::card {:card-number :four :card-color :spades})
;; => val: {:card-number :four, :card-color :spades} fails spec:
;;    :your.namespace/card predicate: card?

If you don't specify a spec, it defaults to any?. Further, this enables generating data based on record definitions:

(gen/sample (s/gen ::card) 3)
;; => (#your.namespace.card{:card-number :four, :card-color :hearts}
;;     #your.namespace.card{:card-number :six, :card-color :hearts}
;;     #your.namespace.card{:card-number :queen, :card-color :diamonds}

If instrumentation is enabled (via clojure.spec.test.alpha/instrument), the constructor is checked using the specs provided for the selector functions:

;; Does not get checked without instrument.
(make-card :ace :heartz)
;; => #your.namespace.card{:card-number :ace :card-color :heartz}

;; Now, with instrumentation.

(make-card :ace :heartz)
;; =>
;; 1. Unhandled clojure.lang.ExceptionInfo
;; Spec assertion failed.
;; ...
;; Problems: 

;; val: :heartz
;; in: [1]
;; failed: #{:spades :diamonds :hearts :clover}
;; spec: :your.namespace/color
;; at: [:args :color]

NOTE: You must keep track of your namespaced keywords manually (e.g. the keywords you use for defining specs). We do not check for collisions, so former definitions with the same name will be overwritten!


The active.clojure.condition namespace implements conditions, specifically crafted exception objects that form a protocol for communicating the cause of an exception, similar to the condition system in R6RS Scheme.


The active.clojure.lens namespace implements lenses. Lenses provide a subtle way to access and update the elements of a structure and are well-known in functional programming languages.


The active.clojure.config namespace implements application configuration via a big map.


The active.clojure.debug namespace implements some useful debugging tools such as a macro pret that prints and returns its argument.

Pattern Matching

The active.clojure.match namespace provides some syntactic sugar for map matching around core.match.

Higher-order Functions

The active.clojure.function namespace provides the same higher order functions that clojure.core does, but implemented via records and IFn, so that the returned "functions" are = if created with = arguments.

These can be very handy for using React-based libraries like Reacl, which can optimize work based on the equality of values.


An example usage of the active.clojure.function namespace can be found at


Copyright © 2014 Active Group GmbH

Distributed under the Eclipse Public License either version 1.0 or (at your option) any later version.

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