#CALC!: an op that threw

#CALC! means that an op threw an exception, or gave no value. Vex catches the exception and makes it an error value. Thus the evaluation stays total.

An op that throws an exceptionoriginABCDreset boxes

app("parseWeight", ref("name"))

FirstBackNextstep 2 of 2

1. ref name @A → "anchor"
2. app parseWeight @A → #CALC!

Result at A: #CALC! "parseWeight" threw an exception

origin	A	B	C	D
result	#CALC! threw	#CALC! threw	#CALC! threw	#CALC! threw

The program applies the free function parseWeight to the name of the box. No domain of the program accepts a string, so the interpreter uses the free function. The function throws, and the result is #CALC!.

Kinds

Kind	Cause
threw	An op, a free function, an extension handler, a fromScalar lift or a valid check threw an exception. A field read through a getter that throws also gives this kind.
undefined-result	An op gave undefined or null.

For the kind threw, the error keeps the exception in the field thrown:

const r = chain.result("A");
if (!r.ok && r.error.kind === "threw") console.error(r.error.thrown);

The types cannot prevent #CALC!, because the code of the op decides when it throws.

The fix

• Find why the op throws. The field thrown holds the exception, and the field op holds the name of the op.
• Give an op a value for each input that its domain accepts. Use an error value or a valid check, not an exception.
• Give a fallback with ifError for an op that can fail.

Refer to error values for the other codes.