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Vex

#VALUE!: a value of the wrong kind

#VALUE! means that a value has the wrong kind for the place where the program uses it. A spreadsheet gives the same code when a formula adds a text to a number.

An argument of the wrong kindorigin
app("add", ref("position"), lit(true))
step 3 of 3

Result at A: #VALUE! argument 1 of "add" is a boolean, not a Vec2

originABCD
result#VALUE! not-instance#VALUE! not-instance#VALUE! not-instance#VALUE! not-instance

The program adds the boolean true to a position. The op add of Vec2Domain declares a domain parameter, so the interpreter checks the argument before the call. The message is argument 1 of "add" is a boolean, not a Vec2.

Kinds

Section titled “Kinds”
Kind Cause
not-instance No domain accepts the receiver of an op, and no free function has the name of the op. Or an argument of a domain parameter is not a value of the domain.
kind-mismatch An argument of a number, boolean or string parameter has another kind. Also a condition of if, and or or, or a where test, that is not a boolean. Also an item of the wrong kind in a list reduction.
bad-expression The expression is not valid. For example, a special form without its arguments, or parse of a text that is not a Vex expression.

How the types prevent it

Section titled “How the types prevent it”

._ lists the ops with the parameter types of each op. Thus ._.add(true) does not compile. A number is a valid argument only for an op that declares liftScalar.

root.from("position")._.add(1);    // correct: add lifts 1 to the vector (1, 1)
root.from("position")._.add(true); // type error: a boolean is not a Vec2
root.from("position")._.dot(5);    // type error: dot does not lift numbers

A program from JSON, or a field with an unknown type, can still give #VALUE! at run time.

The fix

Section titled “The fix”
  • Give a value of the kind that the parameter declares. The domains page lists the parameters of each op.
  • Put the domain of the receiver in the list of vex(...). The interpreter finds the op of a value in the first domain that accepts the value.

Refer to error values for the other codes.