anchor.diff:      let private positionAfterAction action situation = 
           fst (siteAfterAction action situation)
   
  -    let private siteContent site = snd site
  -
  -    let private sitePosition site = fst site
  -
  -    let private situationPosition situation = 
  -        sitePosition situation.current
  -
       let fitness content action = 
           match content, action with
           | Wall, _ -> -5
  
positive.code:     type ActionOutcome = {fitness:int; nextPosition:Position}
      type Site = Position * Content 
      type Situation = {current:Site; north:Site; south:Site; west:Site; east:Site}
  
      let private siteAfterAction action situation =
          match action with
  
negative.code: 
      let outcomeAfterAction action situation =
          let contentAfterAction = situation |> siteAfterAction action |> siteContent
          
          {
              fitness = fitness contentAfterAction action
              nextPosition = 
                  match contentAfterAction with
                  | Wall -> currentPosition situation
                  | _ -> positionAfterAction action situation
          }