I noticed that the order of precedence for operators doesn't exactly conform to the guidelines that the rest of language follows: while in most places the compiler requires the programmer to be explicit (e.g. pack comments), precedence of operators is a (arbitrary?) choice of the compiler that will still confuse people who are used to excusing Aunt Sally.
What I would expect from Ok? is to raise a compiler error on expressions such as a + b * c, and require that the programmer either changes the order, or adds parentheses.