[hcarvalhoalves]

> And, see, I would actually invert further. The declaration should be:

But then you lose pureness, right? The whole point of using high-order functions is allowing you to be as declarative as mathematics, so you can just operate functions together.

Consider that in the first example, I only need to write the implementation for doubling a number n, while the `doubleElements` implementation is too specific, would throw the other half of the code back into imperative land.

[taeric]

Only in my example that relied on mutations. The first can all be implemented with pure functions just fine. Indeed, I was assuming it would be, hence the assignment to a new variable.

I suppose I should have said that the doubleElements implementation would likely be that map one liner. (Though, it needn't be. One could exploit custom knowledge of the domain there to do crazy crap like memoize the calls.)

That make sense?

[hcarvalhoalves]

> Only in my example that relied on mutations. The first can all be implemented with pure functions just fine. Indeed, I was assuming it would be, hence the assignment to a new variable.

Yes, the first example uses pure functions, but I guess you're confusing pure functions with HOFs [1]. The point is only having to write the implementation to double one number, and extrapolating it by composition. Consider that in your example, for instance, you would need a `doubleHash` function for hashes, and so on.

http://en.wikipedia.org/wiki/Higher-order_function

[taeric]

I did not realize we were debating HOF versus pure functions.

That is, I'm fine with using both the pure and HO functions. I just think hiding the HOF ones behind a normal function call is usually a big win for readability.

So, to do the full example:

    elements = [1,2,3,4]
    doubledElements = doubleElements(elements)
    function doubleElements(e) {
        function double(n) { return n*2; }
        return e.map(double);
    }

Where I would assume the "reader" code would only have the first two lines. The rest would be behind the implementation layer. If the double function would be used elsewhere, no need to scope it to doubleElements.