undefined is Tengo's zero value — a distinct type returned by functions that do not explicitly return, and by missing map lookups.
fmt := import("fmt")nothing := func() {}
result := nothing()
fmt.println(is_undefined(result))m := {name: "Tengo"}
fmt.println(is_undefined(m["missing"]))
fmt.println(is_undefined(m["name"]))fmt.println(type_name(result))lookup := func(m, key) {
val := m[key]
if is_undefined(val) {
return "not found"
}
return val
}
fmt.println(lookup(m, "name"))
fmt.println(lookup(m, "missing"))try it
true true false undefined Tengo not found