Verifications for Monad laws according to fantasy-land.
var Maybe = require'monads.maybe'var laws = require'laws'lawsfunctorsidentityMaybeJustasTest verbose: true times: 100// + OK passed 100 tests.
The easiest way is to grab it from NPM. If you're running in a Browser environment, you can use Browserify
$ npm install laws
If you're not using NPM, Download the latest release, and require
var laws = require'laws'
Download the latest release, and require the
Download the latest release, and load the
file. The properties are exposed in the global
$ git clone git://github.com/folktale/laws.git $ cd laws $ npm install $ make bundle
This will generate the
dist/folktale.laws.umd.js file, which you can load in
This library provides properties for verifying the correctness of an implementation of algebraic structures according to the Fantasy Land specification. They do so by generating random inputs and checking if the algebraic laws holds for your structure.
In order to use these properties, your algebraic library needs to implement the
Eq typeclass, defined as:
class Eq a where-- | True if both structures are equivalentisEqual :: a -> a -> Bool
Here's an example of such implementation, for a
var Maybe =/* (...) */return thisisNothing? bisNothing: thisisJust? thisvalue === bvalue/* (...) */
To verify if a data structure conforms to the laws, you need to partially apply
the law to a function that constructs a structure holding a single value. For
example, if you have an
Identity container and want to check if it conforms
to the Semigroup's law of associativity:
// :: a -> Id areturn alawssemigroupassociativitymakeIdasTest verbose: true// + OK passed 100 tests
Note that applying the law to the constructor function gives you back a
Claire property. There are different ways of using this object, but the
easiest one is to use the
asTest(configuration) method to return a test
function. When invoked (with no parameters), this test function will repeatedly
generate random inputs to test if your implementation behaves correctly
according to the laws.
If any of the inputs invalidates the property, an error is thrown with detailed
information about why the property was invalidated. You can control both the
amount of details in the reports, and the number of random tests that are
performed by passing a configuration object to the
asTest method. By default
the reports are concise and only 100 random tests are performed.
class Configuration whereverbose :: Bool -- * whether to output a detailed report or nottimes :: Int -- * number of random tests to perform
Do note that if
verbose is false, no message will be printed to the standard
output by default.
This library assumes an ES5 environment, but can be easily supported in ES3 platforms by the use of shims. Just include es5-shim :)
Copyright (c) 2013 Quildreen Motta.
Released under the MIT licence.