I've criticized sweet-exprs in the past as trying to do too much (https://news.ycombinator.com/item?id=8507385). But the original subset you're implementing here is very useful.
(I'm still opposed to neoteric expressions, because parens before function is The One True Way, especially in the presence of infix: http://arclanguage.org/item?id=16924. But I won't agitate for it again since n-exprs are optional :)
BTW, in searching for the above link I ran across http://arclanguage.org/item?id=18261, which you might find interesting if you hadn't already seen it.
