How does the reduce call work in the reverse() example?

[tsummerall]

I can't find an implementation of reduce() that this line of code works with from your example:

var reverse = reduce(function(acc, x){ return [x].concat(acc); }, []);

Is it a typo or can you provide a link that would explain how this reverse function operates?

And, to demonstrate my further confusion, shouldn't reverse be in the form of a composable pure function with one argument, as in reverse=function(x) {..} in order to be used with compose?

[Bondifrench]

If you are talking from Chapter 5, reduce is actually _.reduce() from the Ramda library, which has been curried.

DrBoolean needs to prefix a few functions explicitly with _., so it's obvious they are coming from a library.

[tsummerall]

Thanks!

This construction is esoteric enough to non-Ramda users that a sidebar about how it operates would be worthwhile I think. As far as I can tell, the commonly-used underscore.js implementation of reduce() wouldn't allow this trick.

In particular I'm not understanding how reduce digests the empty array it's given in the example.

[DrBoolean]

I have a video available that talks about reduce: https://www.youtube.com/watch?v=JZSoPZUoR58

[tsummerall]

That's a great video, thanks!

[jirutka]

@DrBoolean Heh, funny thing: I know you from your talk “Hey Underscore, You're Doing It Wrong!,” but didn’t know that you are Dr. Boolean, until know!

[DrBoolean]

ha, yeah. My avatar is a disguise!

[kdamball]

@DrBoolean YOU'RE THAT DUDE FROM THE UNDERSCORE VIDEO?

[DrBoolean]

haha, yep!

[kdamball]

I know of a few parties later this evening, if you still need one!

[DrBoolean]

ha. Leave it to me to forever ask the world where the party's at.