Safe ad-hoc polymorphism in JavaScript via bilby.js

binary.js

var lib = require('./lib'),
    λ = lib.method('show', lib.isNumber, function(n) {
        return n.toString(2);
    });

exports.showBinaryTimesTwo = λ.bind(λ.showTimesTwo)(λ);

lib.js

var bilby = require('bilby');

module.exports = bilby.property('showTimesTwo', function(n) {
    return this.show(n) + ' + ' + this.show(n) + ' = ' + this.show(n + n);
});

program.js

var binary = require('./binary'),
    words = require('./words');

console.log(binary.showBinaryTimesTwo(1) + ' and ' + words.showWordTimesTwo(100));

words.js

var lib = require('./lib'),
    λ = lib.method('show', lib.isNumber, function(n) {
        return n == 0 ? 'zero' : n == 1 ? 'one' : n == 2 ? 'two' : 'some number';
    });

exports.showWordTimesTwo = λ.bind(λ.showTimesTwo)(λ);