anchor.diff:          let mutable state = state
   
           for i = 0 to len - 1 do
  -            let result, state' = mapping.Invoke (Int32WithMeasure<'Tag> i, array.[i], state)
  +            let result, state' = mapping.Invoke (Tag.ofInt i, array.[i], state)
               results.[i] <- result
               state <- state'
   
  
positive.code:         let mutable state = state
  
          for i = len - 1 downto 0 do
              let result, state' = mapping.Invoke (Int32WithMeasure<'Tag> i, array.[i], state)
              results.[i] <- result
              state <- state'
  
  
negative.code:         let mutable innerState = innerState
  
          for i = 0 to len - 1 do
              let innerState', outerState' = folder.Invoke (Tag.ofInt i, innerState, array.[i], outerState)
              innerState <- innerState'
              outerState <- outerState'
  
  