NB. The queue object template

data =: ''

queue =: monad def 0
'method value' =. 2 {. y.
if. method -: 'type'
    do. 'queue'
  elseif. method -: 'emptyp'
    do. 0 = # data
  elseif. method -: 'enter'
    do. for_effect_only data =: data , < value
  elseif. method -: 'front'
    do. if. 0 = # data
          do. 'front:  queue is empty'
          else. > {. data
        end.
  elseif. method -: 'remove'
    do. if. 0 = # data
          do. 'remove:  queue is empty'
          else. for_effect_only data =: }. data
        end.
  elseif. method -: 'size'
    do. # data
  elseif. method -: 'print'
    do. if. 0 = # data
          do. 'print: queue is empty'
          else. for_effect_only display 'front of queue'
            s =. data
            while. 0 < # s
              do. for_effect_only display > {. s
                  s =. }. s
            end.
        end.
  elseif. 1
    do. root_object method ; value
end.
)