polygamous
v1.0.3
Published
Clojure-style multi-methods for JavaScript.
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Polygamous
Polygamous is a library that implements Clojure-style run-time polymorphism through multi-methods. Methods dispatch on a single argument, based on pattern matching over the different branches of a method after running the value through a dispatch function — which is identity by default.
Example
var method = require('polygamous')
var fib = method()
.when(0, function(n){ return 0 })
.when(1, function(n){ return 1 })
.fallback(function(n){ return fib(n - 1) + fib(n - 2) })
fib(8) // => 21
Installing
The easiest way is to grab it from NPM (use Browserify if you're on a browser):
$ npm install polygamous
If you really want to continue suffering with old and terrible module
systems (or use no module system at all), you can run make bundle
yourself:
$ git clone git://github.com/robotlolita/polygamous
$ cd polygamous
$ npm install
$ make bundle
# Then use `dist/polygamous.umd.js` wherever you want.
Platform support
This library assumes an ES5 environment, but can be easily supported in ES3 platforms by the use of shims. Just include es5-shim :3
Tests
For node:
$ npm test
For the browser:
$ npm install -g brofist-browser
$ make test
$ brofist-browser serve test/specs
# Then point your browsers to the URL on yer console.
API
polygamous(f)
Constructs a new multi-method, optionally using the given dispatch function.
polygamous: (A... -> B) -> method
The dispatch function will be given the arguments that were passed to the multi-method, and should return a new value that'll be used to select the proper method branch.
We check the dispatch value using deep equality, rather than the less
expressive strict equality comparison. This means that [1, 2]
will happily
match any branch that defines [1, 2]
as its dispatch predicate.
By default, the dispatch is done on the identity of the first argument. That
is, the default dispatch function is: function(a){ return a }
.
method:when(a, f)
Adds a new branch to the method, which is executed only when the dispatch value
matches a
.
when: @method => A, (B... -> C) -> method
Adding a condition that already exists will throw an ambiguous-branch
error.
method:fallback(f)
Adds a baseline branch for the method, which is executed if all other branches fail to match the dispatch value.
fallback: @method => (A... -> B) -> method
method:remove(a)
Removes the branch that has a
as its evaluation condition.
remove: @method => A -> method
method:clone()
Creates a new multi-method that fallbacks to this one.
clone: @method => Unit -> method
Do note that overwriting the fallback of the new multi-method will break the relationship.
Licence
MIT/X11.