Minderbinder is a Clojure library for defining unit conversions available at read, compile and run time.

This post is a quick overview. More information is available on the Minderbinder source repo.

Use

Include the following in your Leiningen project.clj file:

[fogus/minderbinder "0.2.0"]

Or include the following in your pom.xml file in the dependencies section:

<dependency>
  <groupId>fogus</groupId>
  <artifactId>minderbinder</artifactId>
  <version>0.2.0</version>
</dependency>

Examples

Minderbinder includes unit conversions for the following units of measure:

• Time: via #unit/time, base is :milliseconds, ns is minderbinder.time
• Length: via #unit/length, base is :meters, ns is minderbinder.length
• Information: via #unit/info, base is :byte, ns is minderbinder.information

Using Minderbinder’s unit reader form

(ns minderbinder.test.core
  (:require minderbinder.time))

(== #unit/time [1 :second]
    #unit/time [1000 :ms])

;;=> true

(== #unit/time [1 :minute 30 :seconds]
    #unit/time [90 :seconds])

;;=> true

Using Minderbinder’s unit parse functions

(ns minderbinder.test.core
  (:require [minderbinder.length :as mbr]))

(mbr/parse-length-unit [1 :km])

;;=> 1000

(mbr/parse-length-unit [1 :ramsden-link])

;;=> 381/1250

Defining custom conversion rules

Defining a unit conversion is accomplished via Minderbinder’s defunits-of macro. The body of the macro expects the following structure:

(defunits-of unit-name base-unit-tag docstring conversion-spec)

The conversion spec part of the body currently allows pairs of mappings defined in reletive terms. The pairs always start with a keyword used as the unit tag. However, the right-hand side of the pair can be one of the following:

1. Number - defines the value of the unit relative to the base unit
2. Vector - defines the value of the unit relative to another contained unit
3. Keyword - defines a single alias for a unit
4. Set - defined one or more aliases for a unit

A simplified version of Minderbinder’s length conversion definition serves as an example:

(defunits-of length :meter
  "The meter is the length of the path 
  traveled by light in vacuum during a 
  time interval of 1/299,792,458 of 
  a second."
   
  :m  :meter                   ;; an alias for the base unit
  :km 1000                     ;; a larger value relative to the base unit
  :km #{kilometer kilometers}  ;; multiple aliases for a unit
  :cm 1/100                    ;; a smaller value relative to the base
  :mm [1/10 :cm])              ;; a value relative to another unit

Generated vars

The defunits-of macro will define three things in the namespace where the defunits-of macro appears:

1. parse-XXX-unit - a function that parses the unit vector according to the conversion spec, returning the total value relative to the base.

2. unit-of-XXX - a macro that allows the for (unit-of-XXX 1 :foo) that returns the total value relative to the base.

3. XXX-table - a map describing the unit conversion rules.

Plans

• ClojureScript integration
• More conversions included by default
• Base unit changing
• Cross-unit conversions via function results
• More plans not yet thought up.

:F