#NUM!: a value that is not finite

#NUM! means that an op gave a number that is not finite, or a domain value that is not valid. A spreadsheet gives the same code for a result that is too large.

A division by the vector (0, 0)originABCDreset boxes

app("divide", ref("position"), lit(0))

FirstBackNextstep 3 of 3

1. ref position @A → (2, 2)
2. lit 0 @A → 0
3. app divide @A → #NUM!

Result at A: #NUM! "divide" gave a value that is not a valid Vec2

origin	A	B	C	D
result	#NUM! invalid-value	#NUM! invalid-value	#NUM! invalid-value	#NUM! invalid-value

The program divides a position by 0. The op divide lifts the number 0 to the vector (0, 0), and each component of the quotient is infinite. The valid check of Vec2Domain finds the infinite components, and the result is #NUM!.

Kinds

Kind	Cause
not-finite	An op gave a number that is not finite: Infinity, -Infinity or NaN.
invalid-value	An op gave a domain value that fails the valid check of its domain.

One policy for each op

Vex checks the result of each op with one policy. A number must be finite. A domain value must pass the valid check of the first domain that accepts it. Thus an infinite value stops at the op that made it, and the trace shows that op. It does not go through more ops as a silent NaN.

The types cannot prevent #NUM!, because it depends on the values at run time.

The fix

• Do not divide by a value with a zero component. Check the divisor first, with an if or a where test.
• Give a fallback with ifError. The last lesson of the tour does this.
• For a domain of your own, give a valid check that finds the values that the domain does not permit.

Refer to error values for the other codes.