Assignment expressions are no longer lvalues (that was a shitty idea). Primary expressions can't be used in the main chunk and in blocks now (except call expressions). Several other expressions are now disallowed too - namely coro, cfn, seq, quote, unquote, enum, clone, new, __FILE__, __LINE__ and the ellipsis (varargs). Other expressions are still allowed. Function literals are not yet disallowed, TODO.