The 'in' is what makes it difficult to understand for someone not familiar with OCaml syntax and semantics. Reason makes it easier.

I've heard that said, but I don't see how it's a big deal. OK, the very first example introducing let bindings would have to come with a sentence like "the 'in' part of 'let ... in' means 'in' just like in English: 'let' the binding be valid 'in' what follows". You don't have to define a whole new syntax where a single sentence in a language tutorial might be enough.

But I admit that I probably can't fully appreciate whether this is really difficult for someone used to JavaScript.

Except when you're in the top level - in which case you don't use `in`. Oh, and don't forget all the nuance of interleaving imperative commands. I'm an experienced OCaml dev and this trips me up (the "ml compared" section of the docs lists some common pitfalls that Reason resolves).

Ah, but here you seem to be talking about when to write 'in'. Reading it is much simpler: Just ignore that it's there, and voilà, you're set.

(I'm an experienced OCaml dev and := versus <- trips me up from time to time when choosing which one to write, but not when reading code.)

Of course, once you know what 'in' means, it's easy to read, but you have to learn it, and get used to it. I've teached programming to students in finance, and this learnt me how much I underestimated the impact small things like that can have on the learning curve (and the motivation).

Yeah, I don't know what doesn't read easily about "let x = 3 in x - 1" -- it is straightforward: x is equal to 3 in the expression "x - 1".

Hmm, the new if syntax really feels like a step backwards. (But I can see why they chose it: the C-like syntax here isn't too much of a burden, and is familiar to a lot of programmers already.)