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module Error = struct
open Concepts.Condition
let not_enumerable () =
condition "not-enumerable"
"A relation was used where the expression must iterate its members, but it does not support \
enumeration. A procedural relation may decide membership without being able to produce it."
empty
end
class type implementation = object
method enumerate : (Handle.t, Concepts.Condition.condition) result
end
type Handle.protocol += Enumerable of implementation
type t = implementation
let make impl = Enumerable (impl :> implementation)
let from handle = Handle.into handle (function Enumerable impl -> Some impl | _ -> None)
let require handle = from handle |> Option.to_result ~none:(Error.not_enumerable ())
let enumerate i = Handle.invoke i (fun o -> o#enumerate)
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