IMPLEMENTATION MODULE Stek;
FROM Info IMPORT InfoTip;

PROCEDURE MakeNull(VAR s : StekTip);
BEGIN
  s.Top := 0
END MakeNull;

PROCEDURE Empty(VAR s : StekTip) : BOOLEAN;
BEGIN
  RETURN s.Top = 0
END Empty;

PROCEDURE Top(VAR s : StekTip;
              VAR x : InfoTip;
              VAR ok : BOOLEAN);
BEGIN
  IF Empty(s) THEN
    ok := FALSE
  ELSE
    ok := TRUE;
    WITH s DO
      x := Element[Top]
    END
  END
END Top;

PROCEDURE Pop(VAR s : StekTip;
              VAR ok : BOOLEAN);
BEGIN
  IF Empty(s) THEN
    ok := FALSE
  ELSE
    ok := TRUE;
    DEC(s.Top)
  END
END Pop;

PROCEDURE Push(VAR s : StekTip;
               x : InfoTip;
               VAR ok : BOOLEAN);
BEGIN
  WITH s DO
    IF Top = Maxstek THEN
      ok := FALSE
    ELSE
      ok := TRUE;
      INC(Top);
      Element[Top] := x
    END
  END
END Push;

END Stek.