Created
June 26, 2013 11:21
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Clojure-inspired multimethod mechanism in JavaScript
Needs * Underscore.js (http://underscorejs.org/)
* QUnit (http://qunitjs.com/) for tests Have a look at unittests for samples.
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| var multimethod = (function(_) { | |
| var method = function(multi, dispatchValue, method) { | |
| multi.methodTable.push([dispatchValue, method]); | |
| return method; | |
| }; | |
| var defaultmethod = function(multi, method) { | |
| multi.default = ["default", method]; | |
| return method; | |
| }; | |
| var multimethod = function(dispatchingFun) { | |
| var multi = function() { | |
| var dispatchValue = dispatchingFun.apply(this, arguments); | |
| var isEqualToDispatchValue = _.compose(_.partial(_.isEqual, dispatchValue), _.first); | |
| var method = _.find(multi.methodTable, isEqualToDispatchValue) || multi.default; | |
| if (method) { | |
| return method[1].apply(this, arguments); | |
| } | |
| throw "no method found to call"; | |
| }; | |
| multi.methodTable = []; | |
| multi.method = _.partial(method, multi); | |
| multi.defaultmethod = _.partial(defaultmethod, multi); | |
| return multi; | |
| }; | |
| return { | |
| multimethod: multimethod, | |
| defaultmethod: defaultmethod, | |
| method: method | |
| }; | |
| })(_); |
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| module("multimethod"); | |
| test("create multimethod with empty dispatching function", function() { | |
| var hamsdi = multimethod.multimethod(function() {}); | |
| ok(hamsdi != null); | |
| equal(typeof hamsdi, "function"); | |
| }); | |
| test("calling empty multimethod should throw", function() { | |
| var hamsdi = multimethod.multimethod(function() {}); | |
| throws(function() { | |
| var o = hamsdi(); | |
| }); | |
| }); | |
| test("if only default method it should always be called", function() { | |
| var hamsdi = multimethod.multimethod(function() {}); | |
| var m = multimethod.defaultmethod(hamsdi, function() { | |
| return "bamsdi"; | |
| }); | |
| equal(hamsdi(), "bamsdi"); | |
| }); | |
| test("defined method should be called when matched", function() { | |
| var hamsdi = multimethod.multimethod(function(arg) { return arg; }); | |
| multimethod.method(hamsdi, "value", function() { | |
| return "bamsdi"; | |
| }); | |
| equal(hamsdi("value"), "bamsdi"); | |
| }); | |
| test("method with matching value should be called", function() { | |
| var hamsdi = multimethod.multimethod(function(arg) { return arg; }); | |
| multimethod.method(hamsdi, "value", function() { | |
| return "bamsdi"; | |
| }); | |
| multimethod.method(hamsdi, "value2", function() { | |
| return "lol"; | |
| }); | |
| equal(hamsdi("value"), "bamsdi"); | |
| equal(hamsdi("value2"), "lol"); | |
| }); | |
| test("matching should support deep comparison", function() { | |
| var hamsdi = multimethod.multimethod(function(arg) { return {a: arg}; }); | |
| multimethod.method(hamsdi, {a: "value"}, function() { | |
| return "bamsdi"; | |
| }); | |
| multimethod.method(hamsdi, {a: "value2"}, function() { | |
| return "lol"; | |
| }); | |
| equal(hamsdi("value"), "bamsdi"); | |
| equal(hamsdi("value2"), "lol"); | |
| }); | |
| test("functions should be callable on multimethod", function() { | |
| var hamsdi = multimethod.multimethod(function(arg) { return {a: arg}; }); | |
| hamsdi.method({a: "value"}, function() { | |
| return "bamsdi"; | |
| }); | |
| hamsdi.method({a: "value2"}, function() { | |
| return "lol"; | |
| }); | |
| equal(hamsdi("value"), "bamsdi"); | |
| equal(hamsdi("value2"), "lol"); | |
| }); | |
| test("showcase: dynamic polymorphism", function() { | |
| var myObj = { | |
| type: 'A', | |
| doIt: multimethod.multimethod(function() {return this.type;}) | |
| }; | |
| myObj.doIt.defaultmethod(function() { | |
| return "default"; | |
| }); | |
| myObj.doIt.method("A", function() { | |
| return "A"; | |
| }); | |
| myObj.doIt.method("B", function() { | |
| return "B"; | |
| }); | |
| equal(myObj.doIt(), "A"); | |
| myObj.type = "B"; | |
| equal(myObj.doIt(), "B"); | |
| myObj.type = "hamsdi"; | |
| equal(myObj.doIt(), "default"); | |
| }); |
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| <!DOCTYPE html> | |
| <html> | |
| <head> | |
| <meta charset="utf-8"> | |
| <title>QUnit basic example</title> | |
| <link rel="stylesheet" href="qunit-1.11.0.css"> | |
| </head> | |
| <body> | |
| <div id="qunit"> | |
| </div> | |
| <div id="qunit-fixture"> | |
| </div> | |
| <script src="underscore-min.js" type="text/javascript"></script> | |
| <script src="multimethod.js" type="text/javascript"></script> | |
| <script src="qunit-1.11.0.js" type="text/javascript"></script> | |
| <script src="test-multimethod.js" type="text/javascript"></script> | |
| </body> | |
| </html> |
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