type IContextSource<'ctx>=
 abstract member Get:'ctx->unit
 abstract member Set:'ctx->'ctx

type Context={Prop1:string;Prop2:string}
type ViewModel()=

 member val Property1 ="" with get,set
 member val Property2 ="" with get,set
 interface IContextSource<Context>
  with member x.Get ctx=x.Property1<-ctx.Prop1
       member x.Set ctx={ctx with Prop1=x.Property1}