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module Error = struct
open Concepts.Condition
let not_a_relation () =
condition "not-a-relation" "A handle was expected to carry the relation protocol and did not"
empty
end
class type implementation = object
method contains : Concepts.Tuple.t -> (bool, Concepts.Condition.condition) result
end
type Handle.protocol += Relation of implementation
type t = implementation
let make impl = Relation (impl :> implementation)
let from handle = Handle.into handle (function Relation impl -> Some impl | _ -> None)
let require handle = from handle |> Option.to_result ~none:(Error.not_a_relation ())
let contains i tuple = Handle.invoke i (fun o -> o#contains tuple)
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