func builtinFuncs() map[string]reflect.Value {
	builtinFuncsOnce.Do(func() {
		builtinFuncsOnce.v = createValueFuncs(builtins())
	})
	return builtinFuncsOnce.v
}

// createValueFuncs turns a FuncMap into a map[string]reflect.Value
func createValueFuncs(funcMap FuncMap) map[string]reflect.Value {
	m := make(map[string]reflect.Value)
	addValueFuncs(m, funcMap)
	return m
}