Meajure
A Clojure library which provides rudimentary math with units capabilities. The name is entirely gtrak's fault. What makes meajure different from other units libraries? There are already several good ones:
The answer is that Meajure operates on algebraic units. Frinj and minderbinder do a good job at converting between units, but they aren't really designed for mixing units in any sort of meaningful way. Meajure on the other hand isn't designed for unit conversion, it's designed for unit tracking.
user> (require '[clojure.algo.generic.arithmetic
:refer [+ - / *]])
user> (require 'meajure.core)
user> (+ #meajure/unit [3 :feet]
#meajure/unit [2 :feet])
#meajure/unit [5, :feet]Right, so as one would expect, addition between values with the same units is meaningful and supported. Subtraction between values with the same units is also supported. What happens if we try to do something funky and mix units in simple arithmetic?
user> (+ #meajure/unit [3 :feet]
#meajure/unit [2 :meters])
AssertionError Assert failed: (units-equal? x y)Right. Adding feet and meters directly is potentially meaningful, in that you can convert between them. This is what Frinj and minderbinder do. Meajure does not support implicit conversions.
Okay, but what about multiplication? How are those operations defined?
user> (* #meajure/unit [3 :feet]
#meajure/unit [2 :feet])
#meajure/unit [6, :feet 2]Awesome! Meajure allows for unit exponentiation... but what about negative exponents and other numeric cases?
user> (* #meajure/unit [1 :doge]
#meajure/unit [(/ 127 10000000) :doge -1 :btc]
#meajure/unit [600 :usd :btc -1])
#meajure/unit [381/50000, :usd]Sweet... unit canceling and negaitve powers work... what about other math operations that affect exponents?
user> (require '[clojure.algo.generic.math-functions
:refer [pow sqrt]])
nil
user> (sqrt #meajure/unit [3.3])
#meajure/unit [1.816590212458495]
user> (sqrt #meajure/unit [5000 :meters 2])
#meajure/unit [70.71067811865476, :meters 1N]
user> (sqrt #meajure/unit [16 :meters 3 :seconds 1])
#meajure/unit [4.0, :seconds 1/2, :meters 3/2]user> (pow #meajure/unit [16 :meters 3 :seconds 1] 2)
#meajure/unit [256.0 :seconds 2 :meters 6]
user> (pow #meajure/unit [16 :meters 3 :seconds 1] 2.2)
#meajure/unit [445.7218884076158,
:seconds 2.2,
:meters 6.6000000000000005]How on earth you'd contrive a power of 2.2 I have no idea, but if you
manage to, Meajure supports it :D.
Because the units are not affected by the floor, ceil, abs and
round operations, these are supported too as provided by
clojure.algo.generic.math-functions.
Other math operations such as logarithms and trig functions are not well defined in terms of the units of the result, and not supported by default. However thanks to the open nature of multimethods they are trivial to implement.
The reader literal syntax for meajure units also provides support for common powers of ten. For example..
user> #meajure/unit [3 :kilo :doge]
#meajure/unit [3000.0, :doge]
user> #meajure/unit [3 :giga :ton :tnt]
#meajure/unit [3.0E9, :tnt, :ton]This composes with normal units just like you'd expect
user> #meajure/unit [16 :tera :feet 2]
#meajure/unit [1.6E13, :feet 2]Unfortunately this comes with the caviat that SI prefixes cannot be
used as name of the first type. For instance, this is defined to be
invalid, because :tera is reserved to mean the SI prefix when it
occurs in the first sequential type exponent position.
user> #meajure/unit [16 :tera 2]
Exception Invalid parser state! Check unit format!License
Copyright © 2014 Reid "arrdem" McKenzie
Distributed under the Eclipse Public License either version 1.0 or (at your option) any later version.
