Previously a JS function body with no return fell through the call/cc
begin as nil, making `(function(){}())` return null and typeof → object.
Spec: falls-off-end gives undefined.
Wrap the call/cc in (let ((__r__ ...)) (if (= __r__ nil) :js-undefined __r__)).
Downside: explicit `return null` also returns nil, but so does (pick
your last expression evaluating to null). For 99% of cases it's
fall-off-end and the fix is correct. Code that genuinely needs
distinguishable null would need separate nil/undef handling in the
evaluator.
Unit 521/522, slice 148/148 unchanged.
Number 73/100 → 74/100 (+1), String 33/100 → 34/100 (+1).
Fixes S15.5.1.1_A1_T1 family (String(function(){}()) should be "undefined").
giles
679d6bd590