30 - A Chain adding function

Don’t say so much, just coding…

Instruction

We want to create a function that will add numbers together when called in succession.

add(1)(2);
// returns 3

We also want to be able to continue to add numbers to our chain.

add(1)(2)(3); // 6
add(1)(2)(3)(4); // 10
add(1)(2)(3)(4)(5); // 15

and so on.

A single call should return the number passed in.

add(1); // 1

We should be able to store the returned values and reuse them.

var addTwo = add(2);
addTwo; // 2
addTwo + 5; // 7
addTwo(3); // 5
addTwo(3)(5); // 10

We can assume any number being passed in will be valid whole number.

Ruby

Init

def add(n)
  # ...
end

Sample Testing

Test.expect(add(1) == 1);
Test.expect(add(1).(2) == 3);
Test.expect(add(1).(2).(3) == 6);

Javascript

Init

function add(n){
  // Let the currying begin!
}

Sample Testing

Test.expect(add(1) == 1);
Test.expect(add(1)(2) == 3);
Test.expect(add(1)(2)(3) == 6);

Thinking

圖片來源：Unsplash Martin Garrido

Hint & Reference

• Ruby
  • Ruby - Fixnum
• JavaScript
  • JS - MDN Object.prototype.valueOf()

Solution

Ruby

# Solution 1
def add(n)
  n
end

class Fixnum
  def call(m)
    self + m
  end
end

# Solution 2
def add(n)
  def call(m)
    return self + m
  end
  return n
end

Javascript

// Solution 1
function add(n){
  var fn = function(x) {
    return add(n + x);
  };
  
  fn.valueOf = function() {
    return n;
  };
  
  return fn;
}

// Solution2
function add(n) {
  const f = x => add(n + x)
  f.valueOf = () => n
  return f;
}