Discussion on: Should Pure Functions Be Self-contained

[George Lampadaridis]

mmm you got me thinking. What if :

var c = 0;
var obj1 = {
        valueOf: function () {
            c++;
            return 1;
        }
    };
var obj2 = {
        valueOf: function () {
            c++
            return 2;
        }
    };
function add(a) {
  return function inner(b) {
    return a + b;
  };
}
console.log(add(obj1)(obj2));
console.log(c);

[George Lampadaridis]

I messed up the code format. Used from stack overflow... Sorry for asking this here, how can I format code in a comment?

[Heiker]

The syntax highlight can be activated with a block closed in triple backticks, and optionaly a language name. Like this:

```javascript
console.log('hello');
// some code
```

[George Lampadaridis]

Thank you sir. Sorry for the irrelevant question again.

[Heiker]

Fair question. This is javascript, right? In a dynamic language you can only write code in a functional style and hope that no one does a trick like the one you did there.

In your example inner becomes impure because valueOf is impure (it changes some state outside of its scope). So if an impure function gets executed inside of a "pure" function than it is no longer pure.

[Ibrahim ben Salah]

obj1.valueOf is not referential transparent!