Typeclasses in Java

TypeClass.java

/*
Copyright (C) Freddy A Cubas "superstar64" 2019
Boost Software License - Version 1.0 - August 17th, 2003

Permission is hereby granted, free of charge, to any person or organization
obtaining a copy of the software and accompanying documentation covered by
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do so, all subject to the following:

The copyright notices in the Software and this entire statement, including
the above license grant, this restriction and the following disclaimer,
must be included in all copies of the Software, in whole or in part, and
all derivative works of the Software, unless such copies or derivative
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THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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SHALL THE COPYRIGHT HOLDERS OR ANYONE DISTRIBUTING THE SOFTWARE BE LIABLE
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import java.util.function.Function;
import java.util.ArrayList;
import java.util.Arrays;

interface TypeNum<A> {
    A add(A left, A right);
    A sub(A left, A right);
    A mul(A left, A right);
    A div(A left, A right);
    A fromInt(int i);
}


class TypeInteger implements TypeNum<Integer> {
    public Integer add(Integer left, Integer right) {
        return left + right;
    }
    public Integer sub(Integer left, Integer right) {
        return left - right;
    }
    public Integer mul(Integer left, Integer right) {
        return left * right;
    }
    public Integer div(Integer left, Integer right) {
        return left / right;
    }

    public Integer fromInt(int i) {
        return new Integer(i);
    }
}

// java doesn't have native support for higher kinded polymorphism so use a workaround
// based on "Lightweight higher-kinded polymorphism"
// http://ocamllabs.io/higher/lightweight-higher-kinded-polymorphism.pdf

interface App<F,A> {
}

// App<ListBrand,A> = ArrayList<A>
interface ListBrand {
    static <A> App<ListBrand,A> inject(ArrayList<A> list) {
        return new ListInstance<A>(list);
    }
    static <A> ArrayList<A> project(App<ListBrand,A> list) {
        return ((ListInstance<A>)list).get;
    }

    static class ListInstance<A> implements App<ListBrand,A> {
        ArrayList<A> get;
        ListInstance(ArrayList<A> get) {
            this.get = get;
        }
    };
}

interface Functor<F> {
    <A,B> App<F,B> map(Function<A,B> function, App<F,A> functor);
}


class ListFunctor implements Functor<ListBrand> {
    public <A,B> App<ListBrand,B> map(Function<A,B> function, App<ListBrand,A> functor) {
        ArrayList<A> list = ListBrand.project(functor);
        ArrayList<B> result = new ArrayList<>();
        for(A elm: list) {
            result.add(function.apply(elm));
        }
        return ListBrand.inject(result);
    }
}


public class TypeClass {

    static <A> A square(TypeNum<A> type, A x) {
        return type.mul(x, x);
    }

    static <F,A> App<F,A> squareAll(TypeNum<A> typeNum, Functor<F> typeFunctor,App<F,A> functor) {
        return typeFunctor.map(a -> square(typeNum,a),functor);
    }

    public static void main(String[] args) {
        ArrayList<Integer> list = new ArrayList<Integer>(Arrays.asList(1, 2, 3, 4));
        ArrayList<Integer> squares = ListBrand.project( squareAll(new TypeInteger(), new ListFunctor(), ListBrand.inject(list)) );
        System.out.println(squares);
    }

}