def duplicates
import bendvy-ecs-core@0.1.0.4/feature.bend as Featureimport Base
57def duplicates(items:List<&2,String>,+seen:List<&2,String>) -> Validation:
58 match items:
59 case []: Valid{}
60 case +name <> rest: repeated(contains(seen,name),name,_ => duplicates(rest,name <> seen))