Unary minus issue (something similar happens in OCaml as well):
-1 acos #=> 0 (expected pi)
This is because it is evaluated as -(1 acos). Instead, use (-1) acos or 1 negate acos.
Also, as seen on IRC:
<bolsen> 1 * 578 + (1 - 1)*578 --> 334084 ... ? :) <geezusfreeek> that's an amazing bug <jer> bolsen, right; because io parses that as 1 *(578 +(1 -(1))) *(578) <jer> and it's not a bug <jer> it's how io is parsed <jer> operator precedence is a major headache