promql/functions.go
func funcScalar(vals []Value, args Expressions, enh *EvalNodeHelper) Vector {
	v := vals[0].(Vector)
	if len(v) != 1 {
		return append(enh.out, Sample{
			Point: Point{V: math.NaN()},
		})
	}
	return append(enh.out, Sample{
		Point: Point{V: v[0].V},
	})
}
func funcScalar(vals []Value, args Expressions, enh *EvalNodeHelper) Vector {
	v := vals[0].(Vector)
	if len(v) != 1 {
		return append(enh.out, Sample{
			Point: Point{V: math.NaN()},
		})
	}
	return append(enh.out, Sample{
		Point: Point{V: v[0].V},
	})
}
// === Scalar(node ValueTypeVector) Scalar ===