MODULE GraphPaper;

CONST 
  OffPage = Unit.In * 20, 
  Wide = 2;

PROC P(unit, div) IS 
  IF 
    INT(div) -> 
      VAR 
        num, i = 0, j, delta, 
        offset = 0 
      IN 
        num := 
          CEILING(OffPage / 
                  unit); 
        delta := unit / div; 
        DO 
          i < num -> 
            j := 0; 
            PS.SetWidth(Wide); 
            DO 
              j < div -> 
                DrawLines(offset); 
                PS.SetWidth(0); 
                offset := 
                  offset + 
                  delta; 
                j := j + 1 
            OD; 
            i := i + 1 
        OD 
      END 
  FI 
END;

PRIVATE PROC DrawLines(x) IS 
  PS.MoveTo((x, 0)); 
  PS.LineTo((x, OffPage)); 
  PS.MoveTo((0, x)); 
  PS.LineTo((OffPage, x)); 
  PS.Stroke() 
END;

PROC Cmd0() IS 
  P(Unit.In, 4) 
END;