Inspired by "FP Concepts" talk by @martinosis at Ruby Montreal.

foo_test.rb

require "minitest/autorun"

module Foo
  class << self
    attr :add, :sub, :mul, :div
  end

  @add = -> (a, b) { a + b }.curry
  @sub = -> (a, b) { a - b }.curry
  @mul = -> (a, b) { a * b }.curry
  @div = -> (a, b) { a / b }.curry
end

class FooTest < Minitest::Test
  def test_add
    assert_equal 5, Foo.add.(2).(3)
  end

  def test_add_with_curry
    add2 = Foo.add.(2)
    assert_equal 7, add2.(5)
  end

  def test_sub
    assert_equal 5, Foo.sub.(7, 2)
  end
end