I don't know if it was autocorrect screwing up or brainfart / fucky fingers (likely the latter I fear), but what I meant to write that clojure can completely prevent the callee from modifying caller data, since it uses persistent collections and persistent collections are naturally immutable.

Sadly by the time I realised the screwup I couldn't edit the comment anymore (one of the really annoying things about HN alongside stripping random characters from comments and the half-assed markup).