anchor.diff:            mutable ParticleIndex : int // operates as a ring-buffer
             Particles : 'a array // operates as a ring-buffer
             Initializer : int64 -> Constraint -> 'a Emitter -> 'a
  -          Behaviors : Behaviors
  +          InPlaceBehavior : int64 -> Constraint -> 'a Emitter -> Output
  +          CompositionalBehaviors : CompositionalBehaviors
             Constraint : Constraint
             Rate : single
             Body : Body
  
positive.code:                 let (particles, outputs) = Behavior<'a, 'b>.run time this (particlesObj :?> 'a array)
                  (particles :> obj, outputs)
  
      /// A collection of behaviors.
      type [<NoEquality; NoComparison>] Behaviors =
          { Behaviors : Behavior FStack }
  
          /// The empty behavior.
          static member empty =
              { Behaviors = FStack.empty }
  
          /// Combine two behaviors.
          static member add behavior behaviors =
              { Behaviors = FStack.conj behavior behaviors.Behaviors }
  
          /// Combine multiple behaviors.
          static member addMany behaviorsMany behaviors =
              { Behaviors = Seq.fold (fun behaviors behavior -> FStack.conj behavior behaviors) behaviors.Behaviors behaviorsMany }
  
          /// Make a collection of behaviors from a sequence of behaviors.
          static member ofSeq seq =
              Behaviors.addMany seq Behaviors.empty
  
          /// Run the behaviors over an array.
          static member run time behaviors (particles : 'a array) =
              let (particles, outputs) =
                  FStack.fold (fun (particles, output) (behavior : Behavior) ->
  
negative.code: 
      /// Describes the body of an instance value.
      type [<NoEquality; NoComparison; Struct>] Body =
          { mutable Position : Vector2
            mutable Rotation : single
            mutable LinearVelocity : single
            mutable AngularVelocity : single
            mutable Gravity : Vector2 }
  
      /// The base particle type.
      type Particle =
  