person00.js

/**
 * 人
 */
var person = function(spec){
    var that = {};
    
    var toString = function(){
        return spec.name + " " + spec.age.toString();
    };
    that.toString = toString;
    
    var getName = function(){
        return spec.name;
    };
    that.getName = getName;
    
    var getAge = function(){
        return spec.age;
    };
    that.getAge = getAge;
    
    return that;
};

/**
 * グループ
 */
var group = function(spec){
    var that = {};
    var persons = [];
    
    var add = function(ps){
        persons[persons.length] = ps;
        return that;
    };
    that.add = add;
    
    var toString = function(){
        return persons.join(",");
    };
    that.toString = toString;
    
    var each = function(f){
        var i;
        for (i = 0; i < persons.length; i++) {
            f(persons[i]);
        }
    };
    that.each = each;
    
    var map = function(f){
        var result = [];
        each(function(ps){
            result[result.length] = f(ps);
        });
        return result;
    };
    that.map = map;
    
    var filter = function(p){
        var result = [];
        each(function(ps){
            if (p(ps)) {
                result[result.length] = ps
            }
        });
        return result;
    };
    that.filter = filter;
    
    var fold = function(z, f){
        var acc = z;
        each(function(ps){
            acc = f(acc, ps);
        });
        return acc;
    };
    that.fold = fold;
    
    return that;
};

var g = group({}).add(person({
    name: "Hanako",
    age: 15
})).add(person({
    name: "Jiro",
    age: 15
})).add(person({
    name: "Tarou",
    age: 21
}));

g.each(function(ps){
    console.log(ps.toString());
});

var g2 = g.map(function(ps){
    return ps.getAge() * 2;
});
console.log(g2.toString());

var g3 = g.filter(function(ps){
    return ps.getAge() < 20;
});
console.log(g3.toString());

var g4 = g.fold(0, function(acc, ps){
    return acc + ps.getAge();
});
console.log(g4.toString());

var g4 = g.fold("", function(acc, ps){
    return acc + ps.getName();
});
console.log(g4.toString());