I think the R6S behavior helps with visual matching, but squanders using square brackets for something more useful (e.g. vectors), which is a shame. Another thing Clojure does is copy Arc in eliminating parentheses around the pairs of forms in let bindings and cond forms, which really aren’t needed. It just expects pairs of forms and the compiler objects if given an odd number. The programmer can use whitespace (notably newlines) to format the code so the pairings are visibly apparent. That reduces a surprising amount of needless parentheses because let binding forms are used all over (less so cond forms).