with-opt-builder.fs

type optionBuilder() =
    member __.Bind(opt, f) = Option.bind f opt
    member __.Bind(obj, f) = Option.bind f (Option.ofObj obj)
    member __.Bind(obj, f) = Option.bind f (Option.ofObj (box obj))
    member __.Bind(obj, f) = Option.bind f (Option.ofNullable obj)
    member __.Return x = Some x
    member __.ReturnFrom x = x

let option = optionBuilder()

type SwaggerDefaultValues () =
    interface IOperationFilter with
        member this.Apply(operation: Operation, context: OperationFilterContext) = 
            option {
                let! op = operation
                let! parameters = operation.Parameters
                return parameters.OfType<NonBodyParameter>()
            } 
            |> Option.defaultValue Seq.empty
            |> Seq.map (fun parameter -> option {
                let! paramDescription = 
                    context.ApiDescription.ParameterDescriptions 
                    |> Seq.tryFind (fun x -> x.Name = parameter.Name)
                let! modelMetadata = description.ModelMetadata
                let! description = modelMetadata.Description
                if isNull parameter.Description then parameter.Description <- description
                let! routeInfo = description.RouteInfo
                if isNull parameter.Default then parameter.Default <- routeInfo.DefaultValue
                parameter.Required <- (parameter.Required || (not routeInfo.IsOptional))
            })
            |> Seq.iter Option.iter