Expressions in Limbo are not reordered by the compiler; values are computed in accordance with the parse of the expression. However there is no guarantee of temporal evaluation order for expressions with side effects, except in the following circumstances: function arguments are fully evaluated before the function is called; the logical operators && and || have fully defined order of evaluation, as explained above. All side effects from an expression in one statement are completed before the next statement is begun.

In an expression containing a constant subexpression (in the sense of §8.5), the constant subexpression is evaluated at compile-time with all exceptions ignored.

Underflow, overflow, and zero-divide conditions during integer arithmetic produce undefined results.

The real arithmetic of Limbo is all performed in IEEE double precision, although denormalized numbers may not be supported. By default, invalid operations, zero-divide, overflow, and underflow during real arithmetic are fatal; inexact-result is quiet. The default rounding mode is round-to-nearest-even. A set of routines in the Math library module permits independent control of these modes within each thread.