def String.join.go
import Base2181def String.join.go(xs: List<&2, String>, h: String, +sep: String) -> String:
2182 match xs:
2183 case Nil{}:
2184 h
2185 case h2 <> t:
2186 String.append(h, String.append(sep, String.join.go(t, h2, sep)))