NB. The queue object template which inherits the print operation

data =: ''

queue_z_ =: monad define
('operation value') =. 2 take y
if. operation match 'type'
    do. 'queue'
  elseif. operation match 'emptyp'
    do. 0 = tally data
  elseif. operation match 'enter'
    do. for_effect_only data =: data , box value
  elseif. operation match 'front'
    do. if. 0 = tally data
          do. 'front:  queue is empty'
          else. open first data
        end.
  elseif. operation match 'remove'
    do. if. 0 = tally data
          do. 'remove:  queue is empty'
          else. for_effect_only data =: rest data
        end.
  elseif. operation match 'size'
    do. tally data
  elseif. operation match 'print'
    do. if. 0 = tally data
          do. 'print: queue is empty'
          else. for_effect_only display 'front of queue'
                print 'print' ; box data
        end.
  elseif. 1
    do. root_object operation ; value
end.
)