class GBN_TUPLE_REQUIRE [G]
	-- matches the routines of GBN_TUPLE, checking
	-- all the require clauses for each routine, and
	-- setting last_error equal to the label of the earliest
	-- violated, if any. Default (all require clauses
	-- satisfied): last_error = "".

feature

  last_error: STRING

  first_place (vt: GBN_TUPLE[G]) is
    do
      if vt . is_empty then
	!! last_error.copy("nonempty")
      else
	!! last_error.copy("")
      end
    end

  last_place (vt: GBN_TUPLE [G]) is
    do
      if vt . is_empty then
	!! last_error.copy("nonempty")
      else
	!! last_error.copy("")
      end
    end

  rank (vt: GBN_TUPLE[G]; p: GBN_PLACE) is
    do
      if not vt . has_place (p) then
	!!last_error.copy ("has_p")
      else
	!!last_error.copy ("")
      end
    end

  nth_after (vt: GBN_TUPLE[G]; n: INTEGER; p: GBN_PLACE) is
    do
      if not vt . has_place (p) then
	!!last_error.copy ("has_p")
      elseif n < 0 then
	!!last_error.copy ("n_nonnegative")
      elseif n > vt . count-1 then
	!!last_error.copy ("n_inrange")
      else
	!!last_error.copy ("")
      end
    end

  nth_before (vt: GBN_TUPLE[G]; n: INTEGER; p: GBN_PLACE) is
    do
      if not vt . has_place (p) then
	!!last_error.copy ("has_p")
      elseif n < 0 then
	!!last_error.copy ("n_nonnegative")
      elseif n > vt . count-1 then
	!!last_error.copy ("n_inrange")
      else
	!!last_error.copy ("")
      end
    end

  nth_place (vt: GBN_TUPLE[G]; n: INTEGER) is
    do
      if n < 0 then
	!!last_error.copy ("n_positive")
      elseif n > vt . count then
	!!last_error.copy ("inrange")
      else
	!!last_error.copy ("")
      end
    end

  pred (vt: GBN_TUPLE[G]; p: GBN_PLACE) is
    do
      if not vt . has_place (p) then
	!!last_error.copy ("has_p")
      else
	!!last_error.copy ("")
      end
    end

  succ (vt: GBN_TUPLE[G]; p: GBN_PLACE) is
    do
      if not vt . has_place (p) then
	!!last_error.copy ("has_p")
      else
	!!last_error.copy ("")
      end
    end

  cyclic_pred (vt: GBN_TUPLE[G]; p: GBN_PLACE) is
    do
      if not vt . has_place (p) then
	!!last_error.copy ("has_p")
      else
	!!last_error.copy ("")
      end
    end

  cyclic_succ (vt: GBN_TUPLE[G]; p: GBN_PLACE) is
    do
      if not vt . has_place (p) then
	!!last_error.copy ("has_p")
      else
	!!last_error.copy ("")
      end
    end

  place_lesseq (vt: GBN_TUPLE[G]; p, q: GBN_PLACE) is
    do
      if not vt . has_place (p) then
	!!last_error.copy ("has_p")
      elseif not vt . has_place (q) then
	!!last_error.copy ("has_q")
      else
	!!last_error.copy ("")
      end
    end

  item (vt: GBN_TUPLE[G]; p: GBN_PLACE) is
    do
      if not vt . has_place (p) then
	!!last_error.copy ("has_p")
      else
	!!last_error.copy ("")
      end
    end

  top (vt: GBN_TUPLE [G]) is
    do
      if vt . is_empty then
	!! last_error.copy("nonempty")
      else
	!! last_error.copy("")
      end
    end

  first_item (vt: GBN_TUPLE [G]) is
    do
      if vt . is_empty then
	!! last_error.copy("nonempty")
      else
	!! last_error.copy("")
      end
    end

  last_item (vt: GBN_TUPLE [G]) is
    do
      if vt . is_empty then
	!! last_error.copy("nonempty")
      else
	!! last_error.copy("")
      end
    end

  cyclic_iterator (vt: GBN_TUPLE[G]; start_at, stop_after: GBN_PLACE) is
    do
      if not vt . has_place ( start_at ) then
	!! last_error.copy("has_start_place")
      elseif not vt . has_place ( stop_after ) then
	!! last_error.copy("has_stop_place")
      else
	!! last_error.copy("")
      end
    end

  reverse_cyclic_iterator (vt: GBN_TUPLE[G]; start_at, stop_after: GBN_PLACE) is
    do
      if not vt . has_place ( start_at ) then
	!! last_error.copy("has_start_place")
      elseif not vt . has_place ( stop_after ) then
	!! last_error.copy("has_stop_place")
      else
	!! last_error.copy("")
      end
    end

  wipe_out (vt: GBN_TUPLE [G]) is
    do
      if vt . is_protected then
	!! last_error.copy("unprotected")
      else
	!! last_error.copy("")
      end
    end

  add_first (vt: GBN_TUPLE[G]; x: G) is
    do
      if vt . is_protected then
	!! last_error.copy("unprotected")
      else
	!! last_error.copy("")
      end
    end

  push (vt: GBN_TUPLE[G]; x: G) is
    do
      if vt . is_protected then
	!! last_error.copy("unprotected")
      else
	!! last_error.copy("")
      end
    end

  add_last (vt: GBN_TUPLE[G]; x: G) is
    do
      if vt . is_protected then
	!! last_error.copy("unprotected")
      else
	!! last_error.copy("")
      end
    end

  add_before (vt: GBN_TUPLE[G]; x: G; p: GBN_PLACE) is
    do
      if vt . is_protected then
	!! last_error.copy("unprotected")
      elseif p /= Void and then not vt . has_place ( p ) then
	!! last_error.copy("p_valid")
      else
	!! last_error.copy("")
      end
    end

  add_after (vt: GBN_TUPLE[G]; x: G; p: GBN_PLACE) is
    do
      if vt . is_protected then
	!! last_error.copy("unprotected")
      elseif p /= Void and then not vt . has_place ( p ) then
	!! last_error.copy("p_valid")
      else
	!! last_error.copy("")
      end
    end

  pop (vt: GBN_TUPLE [G]) is
    do
      if vt . is_protected then
	!! last_error.copy("unprotected")
      elseif vt . is_empty then
	!! last_error.copy("nonempty")
      else
	!! last_error.copy("")
      end
    end

  remove_first (vt: GBN_TUPLE [G]) is
    do
      if vt . is_protected then
	!! last_error.copy("unprotected")
      elseif vt . is_empty then
	!! last_error.copy("nonempty")
      else
	!! last_error.copy("")
      end
    end

  remove_last (vt: GBN_TUPLE [G]) is
    do
      if vt . is_protected then
	!! last_error.copy("unprotected")
      elseif vt . is_empty then
	!! last_error.copy("nonempty")
      else
	!! last_error.copy("")
      end
    end

  remove (vt: GBN_TUPLE[G]; p: GBN_PLACE) is
    do
      if vt . is_protected then
	!! last_error.copy("unprotected")
      elseif not vt . has_place (p) then
	!! last_error.copy("has_p")
      else
	!! last_error.copy("")
      end
    end

  absorb_prefix (vt: GBN_TUPLE[G]; other: GBN_TUPLE[G]) is
    do
      if vt . is_protected then
	!! last_error.copy("unprotected")
      elseif other = Void then
	!! last_error.copy("nonvoid")
      elseif other = vt then
	!! last_error.copy("different")
      else
	!! last_error.copy("")
      end
    end

  absorb_suffix (vt: GBN_TUPLE[G]; other: GBN_TUPLE[G]) is
    do
      if vt . is_protected then
	!! last_error.copy("unprotected")
      elseif other = Void then
	!! last_error.copy("nonvoid")
      elseif other = vt then
	!! last_error.copy("different")
      else
	!! last_error.copy("")
      end
    end

  absorb_before (vt: GBN_TUPLE[G]; other: GBN_TUPLE[G]; p: GBN_PLACE) is
    do
      if vt . is_protected then
	!! last_error.copy("unprotected")
      elseif other = Void then
	!! last_error.copy("nonvoid")
      elseif other = vt then
	!! last_error.copy("different")
      elseif p /= Void and then not vt . has_place (p) then
	!! last_error.copy("p_valid")
      else
	!! last_error.copy("")
      end
    end

  absorb_after (vt: GBN_TUPLE[G]; other: GBN_TUPLE[G]; p: GBN_PLACE) is
    do
      if vt . is_protected then
	!! last_error.copy("unprotected")
      elseif other = Void then
	!! last_error.copy("nonvoid")
      elseif other = vt then
	!! last_error.copy("different")
      elseif p /= Void and then not vt . has_place (p) then
	!! last_error.copy("p_valid")
      else
	!! last_error.copy("")
      end
    end

  cyclic_remove (vt: GBN_TUPLE[G]; p, q: GBN_PLACE;
	subtuple: GBN_BOX[GBN_TUPLE[G]]) is
    do
      if vt . is_protected then
	!! last_error.copy("unprotected")
      elseif not vt . has_place (p) then
	!! last_error.copy("has_p")
      elseif not vt . has_place (q) then
	!! last_error.copy("has_q")
      else
	!! last_error.copy("")
      end
    end

end --- class GBN_TUPLE_REQUIRE