#NAME?: an unknown name

#NAME? means that the program uses a name that Vex does not know: an op or a variable. A spreadsheet gives the same code for a function name with a spelling error.

An op that the domain does not declareorigin

app("explode", ref("position"))

step 2 of 2

Result at A: #NAME? the domain "Vec2" has no op "explode"

origin	A	B	C	D
result	#NAME? unknown-op	#NAME? unknown-op	#NAME? unknown-op	#NAME? unknown-op

The program applies the op explode to a position. Vec2Domain accepts the position, but it does not declare explode. The message is the domain "Vec2" has no op "explode".

Kinds

Kind	Cause
`unknown-op`	The domain of the receiver does not declare the op. An inherited member, for example `toString`, is not an op. Also an op without arguments that is not a free function, and an `ext` kind without a handler.
`unbound`	A `var` reads a name that no `let` binds.

How the types prevent it

._ lists only the ops of the domain of the current value. Thus ._.explode() does not compile. After an op gives a value that no domain of the chain accepts, the chain has no ._.

root.from("position")._.explode();             // type error: Vec2 has no op "explode"
root.from("position")._.length()._.halve();    // type error: halve is not an op of Num

The builder makes the names of with, fork and the axes itself. Thus a program from the builder has no unbound name. The program above is possible only as IR, for example from JSON.

The fix

Use an op of the domain. The domains page lists the ops of each domain.
To add an op, declare it in the ops of the domain. Or set methods: "all", and each method of a value is an op.
For a free function, give it in fns: vex(...domains).withOptions({ fns: { myOp } }).

Refer to error values for the other codes.