2 Interface to the ncurses Library
  
  In  this  chapter  we  describe  the GAP interface to the GNU curses/ncurses
  C-library.  This  library  contains  routines  to manipulate the contents of
  terminal  windows.  It  allows  one to write programs which should work on a
  wide variety of terminal emulations with different sets of capabilities.
  
  This  technical  chapter  is  intended  for  readers who want to program new
  applications  using the ncurses functionality. If you are only interested in
  the  function NCurses.BrowseGeneric (4.3-1) from this package or some of its
  applications you can skip this chapter.
  
  Detailed  documentation of the ncurses library is probably available in your
  operating system (try man ncurses) and from the web (see for example [NCu]).
  Here,  we  only give short reminders about the functions provided in the GAP
  interface and explain how to use the GAP functions.
  
  
  2.1 The ncurses Library
  
  In  this  section we list the functions from the GNU ncurses library and its
  panel  extension which are made available in GAP via the Browse package. See
  the  following  section 2.2 for explanations how to use these functions from
  within GAP.
  
  The  basic  objects  to  manipulate  are  called windows, they correspond to
  rectangular  regions of the terminal screen. Windows can overlap but ncurses
  cannot  handle  this  for  the  display. Therefore windows can be wrapped in
  panels,  they provide a display depth for windows and it is possible to move
  panels to the top and bottom of the display or to hide a panel.
  
  We  will  not  import  all  the functions of the ncurses library to GAP. For
  example,  there  are many pairs of functions with the same name except for a
  leading  w (like move and wmove for moving the cursor in a window). Here, we
  only  import  the versions with w, which get a window as first argument. The
  functions  without w are for the ncurses standard screen window stdscr which
  is  available  as  window  0 in GAP. Similarly, there are functions with the
  same  name  except  for  an extra n (like waddstr and waddnstr for placing a
  string into a window). Here, we only import the safer functions with n which
  get  the  number  of  characters  to  write  as  argument.  (More convenient
  functions are then implemented on the GAP level.)
  
  
  2.1-1 Setting the terminal
  
  We  first  list  flags  for  setting  the basic behavior of a terminal. With
  savetty/resetty a setting can be stored and recovered.
  
  savetty()
        This stores the current setting of the terminal in a buffer.
  
  resetty()
        This  resets  the  terminal  to  what  was  stored in the last call to
        savetty.
  
   cbreak()/nocbreak()
        In  cbreak  mode  each  input  character  from  a terminal is directly
        forwarded to the application (but see keypad). With nocbreak this only
        happens after a newline or return is typed.
  
  keypad(win, bool)
        If  set  to true some special input like arrow or function keys can be
        read  as single characters from the input (such keys actually generate
        certain sequences of characters), see also 2.1-4. (The win argument is
        irrelevant.)
  
   echo()/noecho()
        This  determines  if  input characters are automatically echoed by the
        terminal at the current cursor position.
  
  curs_set(vis)
        This determines the visibility of the cursor. The argument vis=0 makes
        the  cursor  invisible.  With vis=1 it becomes visible; some terminals
        allow also higher levels of visibility.
  
  wtimeout(win, delay)
        Here delay determines a timeout in milliseconds for reading characters
        from  the  input of a window. Negative values mean infinity, that is a
        blocking read.
  
   nl()/nonl()
        With  nl  a return on input is translated to a newline character and a
        newline on output is interpreted as return and linefeed.
  
  intrflush(win, bool)
        This  flag  determines  if  after  an  interrupt pending output to the
        terminal is flushed. (The win argument is irrelevant.)
  
  idlok(win, bool)
        With  true  the  library  tries  to  use  a  hardware  line  insertion
        functionality (in particular for scrolling).
  
  scrollok(win, bool)
        If  set  to true moving the cursor down from the last line of a window
        causes scrolling of the whole window, otherwise nothing happens.
  
  leaveok(win, bool)
        If  set  to  true  a  refresh  of  the window leaves the cursor at its
        current location, otherwise this is not guaranteed.
  
  clearok(win, bool)
        If  set  to  true the next refresh of the window will clear the screen
        completely and redraw everything.
  
  immedok(win, bool)
        If  set to true all changes of the window will automatically also call
        a wrefresh.
  
   raw()/noraw()
        Similar  to  cbreak, usually not needed (see the ncurses documentation
        for details).
  
  
  2.1-2 Manipulating windows
  
  In  ncurses  an  arbitrary number of windows which correspond to rectangular
  regions  (maybe overlapping) of the screen can be handled. You should always
  delete  windows  which  are  no  longer  needed.  To get a proper display of
  overlapping  windows  (which may occur by recursively called functions using
  this library) we suggest that you always wrap windows in panels, see 2.1-3.
  
  For functions which involve coordinates recall that the upper left corner of
  the screen or internally of any window has the coordinates (0,0).
  
  newwin(nlines, ncols, y, x)
        This  creates a new window whose upper left corner has the coordinates
        (y,x) on the screen and has nlines lines and ncols columns, if this is
        possible.  The  arguments  nlines  and  ncols  can be zero, then their
        maximal possible values are assumed.
  
  delwin(win)
        Deletes a window.
  
  mvwin(win, y, x)
        Moves the upper left corner of the window to the given coordinates, if
        the  window  still  fits  on  the  screen.  With panels don't use this
        function, but use move_panel mentioned below.
  
  wrefresh(win)
        Writing  to a window only changes some internal buffers, this function
        copies the window content to the actual display screen. You don't need
        this  function  if  you wrap your windows in panels, use update_panels
        and doupdate instead.
  
  doupdate()
        Use  this function to update the content of your display screen to the
        current  content of all windows. If your terminal is not yet in visual
        mode this function changes to visual mode.
  
  endwin()
        Use  this function to leave the visual mode of your terminal. (Remark:
        If  you  use this function while not in visual mode the cursor will be
        moved  to  the  line  where  the visual mode was started last time. To
        avoid this use isendwin first.)
  
  isendwin()
        Returns true if called while not in visual mode and false otherwise
  
  getbegyx(win)
        Get  the  coordinates  of  the  upper  left  corner of a window on the
        screen.
  
  getmaxyx(win)
        Get the number of lines and columns of a window.
  
  
  2.1-3 Manipulating panels
  
  Wrap  windows  in  panels to get a proper handling of overlapping windows on
  the   display.   Don't   forget  to  delete  a  panel  before  deleting  the
  corresponding window.
  
  new_panel(win)
        Create a panel for a window.
  
  del_panel(pan)
        Delete a panel.
  
  update_panels()
        Use  this  function  to copy changes of windows and panels to a screen
        buffer. Then call doupdate() to update the display screen.
  
  move_panel(pan, y, x)
        Move top left corner of a panel wrapped window to coordinates (y,x) if
        possible.
  
   hide_panel(pan)/show_panel(pan)
        Hide  or  show,  respectively,  the  content of a panel on the display
        screen.
  
   top_panel(pan)/bottom_panel(pan)
        Move a panel to the top or bottom of all panels, respectively.
  
   panel_below(pan)/panel_above(pan)
        Return  the panel directly below or above the given one, respectively.
        With argument 0 the top or bottom panel are returned, respectively. If
        argument  is  the  bottom  or  top  panel, respectively, then false is
        returned.
  
  
  2.1-4 Getting keyboard input
  
  If  you  want to read input from the user first adjust the terminal settings
  of cbreak, keypad, echo, wtimeout and curs_set to your needs, see 2.1-1. The
  basic functions are as follows.
  
  wgetch(win)
        Reads one character from user input (returned as integer). If wtimeout
        was set with a positive delay then the function returns false if there
        was  no input for delay milliseconds. Note that in nocbreak mode typed
        characters  reach  the  application only after typing a return. If the
        keypad  flag  is set to true some special keys can be read like single
        characters; the keys are explained below. (Note that there is only one
        input queue for all windows.)
  
  ungetch(char)
        Puts back the character char on the input queue.
  
  Some  terminals allow one to read special keys like one character, we import
  some  of  the  symbolic  names of such keys into GAP. You can check for such
  characters  by  comparing  with  the  components of the record NCurses.keys,
  these are
  
  UP/DOWN/LEFT/RIGHT
        the arrow keys
  
  PPAGE/NPAGE
        the page up and page down keys
  
  HOME/END
        the home and end keys
  
  BACKSPACE/DC
        the backspace and delete keys
  
  IC
        the insert key
  
  ENTER
        the enter key
  
  F1/F2/../F24
        the function keys
  
  MOUSE
        a pseudo key to detect mouse events
  
  A1/A3/B2/C1/C3
        the keys around the arrow keys on a num pad
  
  It can happen that on a specific keyboard there is no key for some of these.
  Also,  not all terminals can interpret all of these keys. You can check this
  with the function
  
  has_key(key)
        Checks if the special key key is recognized by the terminal.
  
  
  2.1-5 Writing to windows
  
  The  display of text in ncurses windows has two aspects. The first is to get
  actual  characters  on the screen. The second is to specify attributes which
  influence  the  display,  for  example  normal or bold fonts or colors. This
  subsection  is for the first aspect. Possible attributes are explained below
  in 2.1-7.
  
  wmove(win, y, x)
        Moves  the  cursor  to position (y,x), recall that the coordinates are
        zero based, (0,0) being the top left corner.
  
  waddnstr(win, str, len)
        Writes  the  string str to the window starting from the current cursor
        position.  Writes  at  most  len characters. At end of line the cursor
        moves  to  the  beginning of next line. The behavior at the end of the
        window depends on the setting of scrollok, see 2.1-1.
  
  waddch(win, char)
        Writes  a  character  to the window at the current cursor position and
        moves  the  cursor  on. The character char is given as integer and can
        include attribute information.
  
  wborder(win, charlist)
        Draws a border around the window. If charlist is a plain list of eight
        GAP  characters  these  are  taken for left/right/top/bottom sides and
        top-left/top-right/bottom-left/bottom-right corners. Otherwise default
        characters  are  used.  (See  NCurses.WBorder  (2.2-9) for a more user
        friendly interface.)
  
  wvline(win, char, len)
        Writes  a  vertical line of length len (or as long as fitting into the
        window) starting from the current cursor position to the bottom, using
        the character char. If char=0 the default character is used.
  
  whline(win, char, len)
        Same  as  wvline  but  for  horizontal  lines starting from the cursor
        position to the right.
  
  werase(win)
        Deletes all characters in the window.
  
  wclear(win)
        Like werase, but also calls clearok.
  
  wclrtobot(win)
        Deletes all characters from cursor position to the right and bottom.
  
  wclrtoeol(win)
        Deletes all characters from cursor position to end of line.
  
  winch(win)
        Returns  the  character  at  current  cursor  position, as integer and
        including color and attribute information.
  
  getyx(win)
        Returns the current cursor position.
  
  waddstr(win, str)
        Delegates to waddnstr(win, str, Length(str)).
  
  
  2.1-6 Line drawing characters
  
  For  drawing  lines  and  grids  in  a  terminal  window you should use some
  "virtual"  characters  which  are  available  as  components  of  the record
  NCurses.lineDraw.  On  some  terminals  these are nicely displayed as proper
  lines (on others they are simulated by ASCII characters). These are:
  
  BLOCK
        solid block
  
  BOARD
        board of squares
  
  BTEE/LTEE/RTEE/TTEE
        bottom/left/right/top tee
  
  BULLET
        bullet
  
  CKBOARD
        checker board
  
  DARROW/LARROW/RARROW/UARROW
        down/left/right/up arrow
  
  DEGREE
        degree symbol
  
  DIAMOND
        diamond
  
  GEQUAL
        greater than or equal
  
  HLINE/VLINE
        horizontal/vertical line
  
  LANTERN
        lantern symbol
  
  LEQUAL
        less than or equal
  
  LLCORNER/LRCORNER/ULCORNER/URCORNER
        lower left/lower right/upper left/upper right corner
  
  NEQUAL
        not equal
  
  PI
        letter pi
  
  PLMINUS
        plus-minus
  
  PLUS
        crossing lines like a plus
  
  S1/S3/S7/S9
        scan line 1/3/7/9
  
  STERLING
        pound sterling
  
  
  2.1-7 Text attributes and colors
  
  In  addition  to  the  actual characters to be written to the screen the way
  they are displayed can be changed by additional attributes. (There should be
  no  danger  to  mix  up  this  notion  of attributes with the one introduced
  in 'Reference:  Attributes'.)  The  available  attributes  are stored in the
  record NCurses.attrs, they are
  
  NORMAL
        normal display with no extra attributes.
  
  STANDOUT
        displays text in the best highlighting mode of the terminal.
  
  UNDERLINE
        underlines the text.
  
  REVERSE
        display  in  reverse video by exchanging the foreground and background
        color.
  
  BLINK
        displays the text blinking.
  
  DIM
        displays the text half bright.
  
  BOLD
        displays the text in a bold font.
  
  Note  that  not  all  of these work with all types of terminals, or some may
  cause  the  same  display.  Furthermore, if NCurses.attrs.has_colors is true
  there is a list NCurses.attrs.ColorPairs of attributes to set the foreground
  and   background   color.   These   should   be   accessed  indirectly  with
  NCurses.ColorAttr (2.2-1). Attributes can be combined by adding their values
  (internally,  they  are  represented by integers). They can also be added to
  the integer representing a character for use with waddch.
  
  The library functions for setting attributes are:
  
  wattrset(win, attr)
        This  sets  the  default  (combined)  attributes for a window which is
        added  to  all characters written to it; using NCurses.attrs.NORMAL as
        attribute is a reset.
  
   wattron(win, attr)/wattroff(win, attr)
        This  sets  or  unsets  one  or  some default attributes of the window
        without changing the others.
  
  wattr_get(win)
        This returns the current default attribute and default color pair of a
        window.
  
  wbkgdset(win, attr)
        This  is  similar to wattrset but you can also add a character to attr
        which is used as default instead of blanks.
  
  wbkgd(win, attr)
        This  function changes the attributes for all characters in the window
        to attr, also used for further characters written to that window.
  
  
  2.1-8 Low level ncurses mouse support
  
  Many  xterm  based  terminals support mouse events. The recognition of mouse
  events by the ncurses input queue can be switched on and off. If switched on
  and a mouse event occurs, then NCurses.wgetch gets NCurses.keys.MOUSE if the
  keypad   flag   is  true  (see  2.1-4).  If  this  is  read  one  must  call
  NCurses.getmouse  which  reads  further  characters from the input queue and
  interprets  them  as  details on the mouse event. In most cases the function
  NCurses.GetMouseEvent  (2.2-10)  can  be  used  in  applications  (it  calls
  NCurses.getmouse).  The  following  low  level  functions  are  available as
  components of the record NCurses.
  
  The  names  of  mouse  events  which  may be possible are stored in the list
  NCurses.mouseEvents,  which  starts [ "BUTTON1_PRESSED", "BUTTON1_RELEASED",
  "BUTTON1_CLICKED",  "BUTTON1_DOUBLE_CLICKED",  "BUTTON1_TRIPLE_CLICKED", ...
  and contains the same for buttons number 2 to 5 and a few other events.
  
   mousemask(intlist)
        The argument intlist is a list of integers specifying mouse events. An
        entry  i refers to the event described in NCurses.mouseEvents[i+1]. It
        returns  a  record  with components .new (for the current setting) and
        .old (for the previous setting) which are again lists of integers with
        the  same meaning. Note that .new may be different from intlist, it is
        always  the  empty list if the terminal does not support mouse events.
        In  applications  use  NCurses.UseMouse  (2.2-10)  instead of this low
        level function.
  
   getmouse()
        This  function must be called after a key NCurses.keys.MOUSE was read.
        It returns a list with three entries [y, x, intlist] where y and x are
        the  coordinates  of  the character cell where the mouse event occured
        and  intlist describes the event, it should have length one and refers
        to a position in NCurses.mouseEvents.
  
   wenclose(win, y, x)
        This  functions  returns  true  if  the screen position y, x is within
        window win and false otherwise.
  
   mouseinterval(t)
        Sets  the time to recognize a press and release of a mouse button as a
        click  to t milliseconds. (Note that this may have no effect because a
        window manager may catch this.)
  
  
  2.1-9 Miscellaneous function
  
  We  also  provide  the ncurses function mnap(msec) which is a sleep for msec
  milliseconds.
  
  Furthermore,  there  a  two  utilities  which  can be useful for scripts and
  testing,  namely  a check if standard input or standard output are connected
  to   terminals.   These   can   be   called   as   NCurses.IsStdinATty()  or
  NCurses.IsStdoutATty(), respectively.
  
  
  2.2 The ncurses GAP functions
  
  The  functions  of the ncurses library are used within GAP very similarly to
  their  C  equivalents. The functions are available as components of a record
  NCurses with the name of the C function (e.g., NCurses.newwin).
  
  In  GAP  the  ncurses  windows  are  accessed  via  integers (as returned by
  NCurses.newwin).  The  standard  screen  stdscr  from the ncurses library is
  available  as  window  number  0.  But  this  should  not  be used; to allow
  recursive  applications  of ncurses always create a new window, wrap it in a
  panel and delete both when they are no longer needed.
  
  Each  window  can  be  wrapped  in  one  panel which is accessed by the same
  integer. (Window 0 cannot be used with a panel.)
  
  Coordinates  in  windows  are  the  same  zero  based  integers  as  in  the
  corresponding   C   functions.  The  interface  of  functions  which  return
  coordinates is slightly different from the C version; they just return lists
  of   integers   and   you   just   give   the   window  as  argument,  e.g.,
  NCurses.getmaxyx(win) returns a list [nrows, ncols] of two integers.
  
  Characters  to  be written to a window can be given either as GAP characters
  like  'a'  or  as  integers  like INT_CHAR('a') = 97. If you use the integer
  version  you  can also add attributes including color settings to it for use
  with NCurses.waddch.
  
  When writing an application decide about an appropriate terminal setting for
  your visual mode windows, see 2.1-1 and the utility function NCurses.SetTerm
  (2.2-2)  below.  Use  NCurses.savetty()  and  NCurses.resetty()  to save and
  restore the previous setting.
  
  We  also  provide  some  higher level functionality for displaying marked up
  text, see NCurses.PutLine (2.2-6) and NCurses.IsAttributeLine (2.2-3).
  
  We  now  describe  some  utility  functions  for  putting text on a terminal
  window.
  
  2.2-1 NCurses.ColorAttr
  
  NCurses.ColorAttr( fgcolor, bgcolor )  function
  Returns:  an attribute for setting the foreground and background color to be
            used on a terminal window (it is a GAP integer).
  
  NCurses.attrs.has_colors global variable
  
  The return value can be used like any other attribute as described in 2.1-7.
  The arguments fgcolor and bgcolor can be given as strings, allowed are those
  in  [  "black", "red", "green", "yellow", "blue", "magenta", "cyan", "white"
  ].  These  are  the  default  foreground  colors  0  to 7 on ANSI terminals.
  Alternatively, the numbers 0 to 7 can be used directly as arguments.
  
  Note  that terminals can be configured in a way such that these named colors
  are not the colors which are actually displayed.
  
  The  variable  NCurses.attrs.has_colors  is  set  to  true  or  false if the
  terminal  supports  colors  or  not,  respectively.  If  a terminal does not
  support colors then NCurses.ColorAttr always returns NCurses.attrs.NORMAL.
  
  For  an  attribute  setting the foreground color with the default background
  color of the terminal use -1 as bgcolor or the same as fgcolor.
  
    Example  
    gap> win := NCurses.newwin(0,0,0,0);; pan := NCurses.new_panel(win);;
    gap> defc := NCurses.defaultColors;;
    gap> NCurses.wmove(win, 0, 0);;
    gap> for a in defc do for b in defc do
    >      NCurses.wattrset(win, NCurses.ColorAttr(a, b));
    >      NCurses.waddstr(win, Concatenation(a,"/",b,"\t"));
    >    od; od;
    gap> if NCurses.IsStdoutATty() then
    >      NCurses.update_panels();; NCurses.doupdate();;
    >      NCurses.napms(5000);;     # show for 5 seconds
    >      NCurses.endwin();; NCurses.del_panel(pan);; NCurses.delwin(win);;
    >    fi;
  
  
  2.2-2 NCurses.SetTerm
  
  NCurses.SetTerm( [record] )  function
  
  This  function  provides a unified interface to the various terminal setting
  functions of ncurses listed in 2.1-1. The optional argument is a record with
  components  which  are assigned to true or false. Recognised components are:
  cbreak,  echo,  nl,  intrflush,  leaveok,  scrollok,  keypad,  raw (with the
  obvious meaning if set to true or false, respectively).
  
  The  default, if no argument is given, is rec(cbreak := true, echo := false,
  nl  := false, intrflush := false, leaveok := true, scrollok := false, keypad
  :=  true).  (This is a useful setting for many applications.) If there is an
  argument  record,  then  the  given  components  overwrite the corresponding
  defaults.
  
  2.2-3 NCurses.IsAttributeLine
  
  NCurses.IsAttributeLine( obj )  function
  Returns:  true if the argument describes a string with attributes.
  
  An  attribute  line describes a string with attributes. It is represented by
  either  a  string  or  a  dense  list  of  strings,  integers,  and Booleans
  immediately  following integers, where at least one list entry must not be a
  string.  (The  reason  is  that we want to be able to distinguish between an
  attribute  line and a list of such lines, and that the case of plain strings
  is  perhaps  the  most  usual  one, so we do not want to force wrapping each
  string  in  a  list.)  The integers denote attribute values such as color or
  font  information,  the  Booleans  denote  that  the  attribute given by the
  preceding integer is set or reset.
  
  If  an integer is not followed by a Boolean then it is used as the attribute
  for  the  following  characters,  that  is  it overwrites all previously set
  attributes. Note that in some applications the variant with explicit Boolean
  values  is preferable, because such a line can nicely be highlighted just by
  prepending a NCurses.attrs.STANDOUT attribute.
  
  For an overview of attributes, see 2.1-7.
  
    Example  
    gap> NCurses.IsAttributeLine( "abc" );
    true
    gap> NCurses.IsAttributeLine( [ "abc", "def" ] );
    false
    gap> NCurses.IsAttributeLine( [ NCurses.attrs.UNDERLINE, true, "abc" ] );
    true
    gap> NCurses.IsAttributeLine( "" );  NCurses.IsAttributeLine( [] );
    true
    false
  
  
  The  empty  string is an attribute line whereas the empty list (which is not
  in IsStringRep (Reference: IsStringRep)) is not an attribute line.
  
  2.2-4 NCurses.ConcatenationAttributeLines
  
  NCurses.ConcatenationAttributeLines( lines[, keep] )  function
  Returns:  an attribute line.
  
  For  a  list lines of attribute lines (see NCurses.IsAttributeLine (2.2-3)),
  NCurses.ConcatenationAttributeLines  returns  the attribute line obtained by
  concatenating the attribute lines in lines.
  
  If  the  optional  argument  keep is true then attributes set in an entry of
  lines  are  valid  also  for  the  following entries of lines. Otherwise (in
  particular  if  there  is  no  second  argument) the attributes are reset to
  NCurses.attrs.NORMAL between the entries of lines.
  
    Example  
    gap> plain_str:= "hello";;
    gap> with_attr:= [ NCurses.attrs.BOLD, "bold" ];;
    gap> NCurses.ConcatenationAttributeLines( [ plain_str, plain_str ] );
    "hellohello"
    gap> NCurses.ConcatenationAttributeLines( [ plain_str, with_attr ] );
    [ "hello", 2097152, "bold" ]
    gap> NCurses.ConcatenationAttributeLines( [ with_attr, plain_str ] );
    [ 2097152, "bold", 0, "hello" ]
    gap> NCurses.ConcatenationAttributeLines( [ with_attr, with_attr ] );
    [ 2097152, "bold", 0, 2097152, "bold" ]
    gap> NCurses.ConcatenationAttributeLines( [ with_attr, with_attr ], true );
    [ 2097152, "bold", 2097152, "bold" ]
  
  
  2.2-5 NCurses.RepeatedAttributeLine
  
  NCurses.RepeatedAttributeLine( line, width )  function
  Returns:  an attribute line.
  
  For  an  attribute  line  line  (see  NCurses.IsAttributeLine (2.2-3)) and a
  positive  integer  width, NCurses.RepeatedAttributeLine returns an attribute
  line   with   width   displayed  characters  (see NCurses.WidthAttributeLine
  (2.2-7))  that is obtained by concatenating sufficiently many copies of line
  and cutting off a tail if applicable.
  
    Example  
    gap> NCurses.RepeatedAttributeLine( "12345", 23 );
    "12345123451234512345123"
    gap> NCurses.RepeatedAttributeLine( [ NCurses.attrs.BOLD, "12345" ], 13 );
    [ 2097152, "12345", 0, 2097152, "12345", 0, 2097152, "123" ]
  
  
  2.2-6 NCurses.PutLine
  
  NCurses.PutLine( win, y, x, lines[, skip] )  function
  Returns:  true if lines were written, otherwise false.
  
  The   argument   lines   can   be   a   list   of   attribute   lines   (see
  NCurses.IsAttributeLine  (2.2-3))  or a single attribute line. This function
  writes the attribute lines to window win at and below of position y, x.
  
  If  the  argument  skip  is given, it must be a nonnegative integer. In that
  case  the  first  skip  characters of each given line are not written to the
  window (but the attributes are).
  
  2.2-7 NCurses.WidthAttributeLine
  
  NCurses.WidthAttributeLine( line )  function
  Returns:  number of displayed characters in an attribute line.
  
  For  an  attribute  line  line  (see  NCurses.IsAttributeLine  (2.2-3)), the
  function returns the number of displayed characters of line.
  
    Example  
    gap> NCurses.WidthAttributeLine( "abcde" );
    5
    gap> NCurses.WidthAttributeLine( [ NCurses.attrs.BOLD, "abc",
    >        NCurses.attrs.NORMAL, "de" ] );
    5
  
  
  2.2-8 NCurses.Grid
  
  NCurses.Grid( win, trow, brow, lcol, rcol, rowinds, colinds )  function
  
  This  function  draws  a grid of horizontal and vertical lines on the window
  win,  using  the  line  drawing  characters  explained  in  2.1-6. The given
  arguments  specify  the  top  and bottom row of the grid, its left and right
  column, and lists of row and column numbers where lines should be drawn.
  
    Example  
    gap> fun := function() local win, pan;
    >      win := NCurses.newwin(0,0,0,0);
    >      pan := NCurses.new_panel(win);
    >      NCurses.Grid(win, 2, 11, 5, 22, [5, 6], [13, 14]);
    >      NCurses.PutLine(win, 12, 0, "Press <Enter> to quit");
    >      NCurses.update_panels(); NCurses.doupdate();
    >      NCurses.wgetch(win);
    >      NCurses.endwin();
    >      NCurses.del_panel(pan); NCurses.delwin(win);
    > end;;
    gap> fun();
  
  
  2.2-9 NCurses.WBorder
  
  NCurses.WBorder( win[, chars] )  function
  
  This  is  a convenient interface to the ncurses function wborder. It draws a
  border  around  the  window  win. If no second argument is given the default
  line drawing characters are used, see 2.1-6. Otherwise, chars must be a list
  of   GAP   characters  or  integers  specifying  characters,  possibly  with
  attributes.  If  chars  has  length  8  the  characters  are  used  for  the
  left/right/top/bottom  sides and top-left/top-right/bottom-left/bottom-right
  corners.  If chars contains 2 characters the first is used for the sides and
  the  second for all corners. If chars contains just one character it is used
  for all sides including the corners.
  
  
  2.2-10 Mouse support in ncurses applications
  
  NCurses.UseMouse( on )  function
  Returns:  a record
  
  NCurses.GetMouseEvent(  )  function
  Returns:  a list of records
  
  ncurses  allows on some terminals (xterm and related) to catch mouse events.
  In  principle  a subset of events can be caught, see mousemask in 2.1-8. But
  this  does  not  seem  to  work  well with proper subsets of possible events
  (probably   due  to  intermediate  processes  X,  window  manager,  terminal
  application,  ...).  Therefore  we  suggest  to catch either all or no mouse
  events in applications.
  
  This  can  be done with NCurses.UseMouse with argument true to switch on the
  recognition of mouse events and false to switch it off. The function returns
  a record with components .new and .old which are both set to the status true
  or  false from after and before the call, respectively. (There does not seem
  to   be   a   possibility   to   get  the  current  status  without  calling
  NCurses.UseMouse.)  If you call the function with argument true and the .new
  component  of  the result is false, then the terminal does not support mouse
  events.
  
  When the recognition of mouse events is switched on and a mouse event occurs
  then  the  key NCurses.keys.MOUSE is found in the input queue, see wgetch in
  2.1-4.  If  this key is read the low level function NCurses.getmouse must be
  called  to  fetch  further details about the event from the input queue, see
  2.1-8.   In   many   cases   this  can  be  done  by  calling  the  function
  NCurses.GetMouseEvent  which  also  generates  additional  information.  The
  return  value  is a list of records, one for each panel over which the event
  occured,  these  panels  sorted  from top to bottom (so, often you will just
  need  the first entry if there is any). Each of these records has components
  .win,  the  corresponding  window  of  the  panel,  .y  and .x, the relative
  coordinates  in  window  .win  where the event occured, and .event, which is
  bound  to  one  of  the  strings  in NCurses.mouseEvents which describes the
  event.
  
  Suggestion:  Always  make the use of the mouse optional in your application.
  Allow  the  user  to switch mouse usage on and off while your application is
  running.  Some users may not like to give mouse control to your application,
  for  example  the  standard cut and paste functionality cannot be used while
  mouse events are caught.
  
  2.2-11 NCurses.SaveWin
  
  NCurses.SaveWin( win )  function
  NCurses.StringsSaveWin( cont )  function
  NCurses.RestoreWin( win, cont )  function
  NCurses.ShowSaveWin( cont )  function
  Returns:  a GAP object describing the contents of a window.
  
  These  functions  can  be  used  to save and restore the contents of ncurses
  windows.  NCurses.SaveWin  returns  a  list [nrows, ncols, chars] giving the
  number  of  rows,  number  of columns, and a list of integers describing the
  content  of  window  win.  The  integers in the latter contain the displayed
  characters plus the attributes for the display.
  
  The  function  NCurses.StringsSaveWin  translates  data  cont in form of the
  output  of NCurses.SaveWin to a list of nrows strings giving the text of the
  rows  of  the  saved  window,  and ignoring the attributes. You can view the
  result with NCurses.Pager (3.1-4).
  
  The  argument  cont for NCurses.RestoreWin must be of the same format as the
  output  of NCurses.SaveWin. The content of the saved window is copied to the
  window win, starting from the top-left corner as much as it fits.
  
  The  utility  NCurses.ShowSaveWin  can  be  used  to  display  the output of
  NCurses.SaveWin (as much of the top-left corner as fits on the screen).