Typescript implementation of https://github.com/Dobiasd/articles/blob/master/from_oop_to_fp_-_inheritance_and_the_expression_problem.md

bar.ts

/// <reference path='dst/ramda.d.ts' />
import R = require('ramda');
import Basic = require('./base');

import Base = Basic.Base;

module Bar {
    export function bar(s: string): Base {
        return {
            step: stepBar(s),
            display: displayBar(s)
        };
    }

    var stepBar = R.curry(function(s: string, delta: number): Base {
        return bar(s + ' ' + delta.toString());
    });

    var displayBar = function(s: string): string {
        return s;
    }
}
export = Bar;

base.ts

module Base {

    export interface Base {
        step(i: number): Base;
        display: string;
    }

}
export = Base;

foo.ts

/// <reference path='dst/ramda.d.ts' />
import R = require('ramda');
import Basic = require('./base');

import Base = Basic.Base;

module Foo {
    export function foo(i: number): Base {
        return {
            step: stepFoo(i),
            display: displayFoo(i)
        };
    }

    var stepFoo = R.curry(function(i: number, delta: number): Base {
        return foo(i+delta);
    });

    var displayFoo = function(i: number): string {
        return i.toString();
    }
}
export = Foo;

main.ts

/// <reference path='dst/ramda.d.ts' />
import R = require('ramda');
import Basic = require('./base');
import Foo = require('./foo');
import Bar = require('./bar');

import Base = Basic.Base;

function stepAll(l: Base[]): Base[] {
    return R.map(function(b: Base) {
        return b.step(1);
    }, l);
}

function displayAll(l: Base[]) {
    return R.map(function(b: Base) {
        return b.display;
    }, l).join('\n');
}

(function main() {
    var l: Base[] = [Foo.foo(0), Bar.bar('')];

    var l1 = stepAll(stepAll(l));

    console.log(displayAll(l1));
})();