chap5.txt

  
  5 Browsing Tables in GAP using ncurses –The Programming Interface
  
  This  chapter  describes  some  aspects of the internals of the browse table
  handling.  The  relevant  objects  are  action  functions that implement the
  individual  navigation steps (see Section 5.1), modes that describe the sets
  of  available  navigation  steps  in given situations (see Section 5.2), and
  browse  applications that are given by the combination of several modes (see
  Section 5.3).  Most  of  the  related  data is stored in the global variable
  BrowseData  (5.4-1).  For more details, one should look directly at the code
  in the file lib/browse.gi of the Browse package.
  
  
  5.1 Navigation Steps in Browse Tables
  
  Navigating  in  a  browse  table  means  that  after entering visual mode by
  calling NCurses.BrowseGeneric (4.3-1), the user hits one or several keys, or
  uses  a  mouse  button,  and  if  this input is in a given set of admissible
  inputs  then  a  corresponding function is executed with argument the browse
  table  (plus  additional  information  in  the  case  of  mouse events). The
  function  call  then  may  change  components  in  this  table (recommended:
  components in its dynamic component), such that the appearance in the window
  may  be  different  afterwards,  and  also  the  admissible inputs and their
  effects may have changed.
  
  The  relation  between the admissible inputs and the corresponding functions
  is  application  dependent. However, it is recommended to associate the same
  input  to  the same function in different situations; for example, the ? key
  and  the  F1  key  should belong to a function that shows a help window (see
  Section  5.4-4),  the q key and the Esc key should belong to a function that
  exits  the  current  mode  (Note that the Esc key may be recognized as input
  only  after  a  delay  of  about  a  second.),  the Q key should belong to a
  function  that  exits the browse application (see Section 5.4-6), the F2 key
  should  belong  to  a  function  that saves the current window contents in a
  global  variable  (see  Section  5.4-5),  and  the  E key should belong to a
  function  that enters a break loop (see Section 5.4-7). The Enter and Return
  keys  should  belong to a click on a selected table entry, and if a category
  row  is  selected  then they should expand/collapse this category. The M key
  should toggle enabling and disabling mouse events. Mouse events on a cell or
  on  a  category row of a browse table should move the selected entry to this
  position; it is recommended that no functionality is lost if no mouse events
  are  used,  although  the number of steps might be reduced when the mouse is
  used.
  
  Each  such function is wrapped into a record with the components action (the
  function  itself)  and  helplines  (a list of attribute lines that describes
  what  the  function  does).  The  help lines are used by the help feature of
  NCurses.BrowseGeneric, see Section 5.4-4.
  
  The  action  functions  need  not return anything. Whenever the shown screen
  shall  be  recomputed after the function call, the component dynamic.changed
  of the browse table must be set to true by the action functions.
  
  After  entering the first characters of an admissible input that consists of
  more  characters,  the  last  line of the window with the browse table shows
  these  characters  behind the prefix partial input:. One can delete the last
  entered  character  of a partial input via the Delete and Backspace keys. It
  is  not  possible  to  make  these  keys part of an admissible input. When a
  partial  input  is  given, only those user inputs have an effect that extend
  the  partial input to (a prefix of) an admissible input. For example, asking
  for  help  by  hitting the ? key will in general not work if a partial input
  had been entered before.
  
  
  5.2 Modes in Browse Tables
  
  In  different  situations,  different  inputs may be admissible for the same
  browse  table,  and  different  functions  may belong to the same input. For
  example,  the meaning of moving down can be different depending on whether a
  cell is selected or not.
  
  The  set  of  admissible  user  inputs  and  corresponding  functions  for a
  particular  situation  is  collected  in  a mode of the browse table. (There
  should  be  no  danger  to  mix  up this notion of mode with the visual mode
  introduced  in  Section 1.1.)  A  mode  is  represented by a record with the
  components  name (a string used to associate the mode with the components of
  header, headerLength, footer, footerLength, Click, and for the help screen),
  flag  (a  string that describes properties of the mode but that can be equal
  for  different  modes), actions (a list of records describing the navigation
  steps that are admissible in the mode, see Section 5.1), and ShowTables (the
  function  used  to eventually print the current window contents, the default
  is  BrowseData.ShowTables). Due to the requirement that each admissible user
  input uniquely determines a corresponding function, no admissible user input
  can be a prefix of another admissible input, for the same mode.
  
  Navigation  steps  (see Section 5.1) can change the current mode or keep the
  mode.  It  is  recommended  that each mode has an action to leave this mode;
  also an action to leave the browse table application is advisable.
  
  In  a  browse  table,  all  available  modes  are  stored  in  the component
  work.availableModes, whose value is a list of mode records. The value of the
  component  dynamic.activeModes  is  a list of mode records that is used as a
  stack: The current mode is the last entry in this list, changing the current
  mode  is  achieved  by  unbinding the last entry (so one returns to the mode
  from  which  the current mode had been entered by adding it to the list), by
  adding  a  new mode record (so one can later return to the current mode), or
  by  replacing  the  last  entry  by  another  mode  record.  As  soon as the
  dynamic.activeModes  list  becomes  empty,  the  browse table application is
  left.  (In this situation, if the browse table had been entered from the GAP
  prompt then visual mode is left, and one returns to the GAP prompt.)
  
  The  following  modes  are  predefined  by the Browse package. Each of these
  modes  admits  the user inputs ?, F1, q, Esc, Q, F2, E, and M that have been
  mentioned in Section 5.1.
  
  browse
        This  mode  admits  scrolling  of  the  browse table by a cell or by a
        screen,  searching  for  a  string,  selecting  a row, a column, or an
        entry, and expanding or collapsing all category rows.
  
  help
        This  mode  is entered by calling BrowseData.ShowHelpTable; it shows a
        help  window  concerning  the actions available in the mode from which
        the  help mode was entered. The help mode admits scrolling in the help
        table by a cell or by a screen. See Section 5.4-4 for details.
  
  select_entry
        In  this  mode,  one  table cell is regarded as selected; this cell is
        highlighted using the attribute in the component work.startSelect as a
        prefix  of  each  attribute line, see the remark in Section 2.2-3. The
        mode  admits  moving the selection by one cell in the four directions,
        searching  for  a  string  and for further occurrences of this string,
        expanding or collapsing the current category row or all category rows,
        and  executing  the  click  function  of  this mode, provided that the
        component work.Click.( "select_entry" ) of the browse table is bound.
  
  select_row
        This  is  like  the  select_entry mode, except that a whole row of the
        browse  table  is highlighted. Searching is restricted to the selected
        row, and click refers to the function work.Click.( "select_row" ).
  
  select_row_and_entry
        This  is  a  combination  of  the select_entry mode and the select_row
        mode.
  
  select_column
        This is like the select_row mode, just a column is selected not a row.
  
  select_column_and_entry
        This  is like the select_row_and_entry mode, just a column is selected
        not a row.
  
  
  5.3 Browse Applications
  
  The  data in a browse table together with the set of its available modes and
  the  stack of active modes forms a browse application. So the part of or all
  functionality of the Browse package can be available (standard application),
  or  additional functionality can be provided by extending available modes or
  adding new modes.
  
  When  NCurses.BrowseGeneric (4.3-1) has been called with the browse table t,
  say, the following loop is executed.
  
  1   If the list t.dynamic.activeModes is empty then exit the browse table,
        and  if the component t.dynamic.Return is bound then return its value.
        Otherwise proceed with step 2.
  
  2   If  t.dynamic.changed is true then call the ShowTables function of the
        current mode; this causes a redraw of the window that shows the browse
        table. Then go to step 3.
  
  3   Get one character of user input. If then the current user input string
        is  the  name  of  an  action  of  the  current  mode  then  call  the
        corresponding  action  function  and go to step 1; if the current user
        input  string  is  just  a  prefix  of the name of some actions of the
        current  mode  then  go to step 3; if the current user input string is
        not a prefix of any name of an action of the current mode then discard
        the last read character and go to step 3.
  
  When  one  designs  a  new  application,  it may be not obvious whether some
  functionality  shall  be implemented via one mode or via several modes. As a
  rule  of  thumb,  introducing a new mode is recommended when one needs a new
  set  of  admissible  actions  in a given situation, and also if one wants to
  allow  the  user  to perform some actions and then to return to the previous
  status.
  
  
  5.4 Predefined Browse Functionalities
  
  5.4-1 BrowseData
  
  BrowseData global variable
  
  This  is  the  record  that  contains  the  global data used by the function
  NCurses.BrowseGeneric  (4.3-1).  The  components  are actions, defaults, and
  several capitalized names for which the values are functions.
  
  BrowseData.actions  is  a  record  containing  the  action  records that are
  provided by the package, see Section 5.1. These actions are used in standard
  applications of NCurses.BrowseGeneric (4.3-1). Of course there is no problem
  with using actions that are not stored in BrowseData.actions.
  
  BrowseData.defaults  is  a  record that contains the defaults for the browse
  table used as the first argument of NCurses.BrowseGeneric (4.3-1). Important
  components  have been described above, see BrowseData.IsBrowseTable (4.2-3),
  in the sense that these components provide default values of work components
  in browse tables. Here is a list of further interesting components.
  
  The following components are provided in BrowseData.defaults.work.
  
  windowParameters
        is  a  list  of  four  nonnegative integers, denoting the arguments of
        NCurses.newwin  for  the  window  in  which  the browse table shall be
        shown. The default is [ 0, 0, 0, 0 ], i. e., the window for the browse
        table is the full screen.
  
  minyx
        is  a  list  of  length  two,  the  entries must be either nonnegative
        integers,  denoting  the  minimal  number of rows and columns that are
        required  by  the  browse  table, or unary functions that return these
        values  when they are applied to the browse table; this is interesting
        for  applications  that  do not support scrolling, or for applications
        that may have large row or column labels tables. The default is a list
        with  two functions, the return value of the first function is the sum
        of the heights of the table header, the column labels table, the first
        table  row,  and  the table footer, and the return value of the second
        function is the sum of widths of the row labels table and the width of
        the  first  column.  (If the header/footer is given by a function then
        this part of the table is ignored in the minyx default.) Note that the
        conditions  are  checked  only  when  NCurses.BrowseGeneric (4.3-1) is
        called, not after later changes of the screen size in a running browse
        table application.
  
  align
        is  a substring of "bclt", which describes the alignment of the browse
        table  in  the window. The meaning and the default are the same as for
        BrowseData.IsBrowseTableCellData  (4.2-1). (Of course this is relevant
        only if the table is smaller than the window.)
  
  headerLength
        describes  the  lengths  of  the headers in the modes for which header
        functions  are  provided.  The value is a record whose component names
        are  names  of  modes and the corresponding components are nonnegative
        integers. This component is ignored if the header component is unbound
        or  bound  to  a  list,  missing  values  are computed by calls to the
        corresponding header function as soon as they are needed.
  
  footerLength
        corresponds to footer in the same way as headerLength to header.
  
  Main
        if  bound  to  a  function  then  this function can be used to compute
        missing  values  for  the  component  main;  this  way  one  can avoid
        computing/storing  all main values at the same time. The access to the
        entries   of   the   main   matrix   is   defined   as   follows:   If
        mainFormatted[i][j] is bound then take it, if main[i][j] is bound then
        take  it and compute the formatted version, if Main is a function then
        call  it  with  arguments  the browse table, i, and j, and compute the
        formatted   version,   otherwise  compute  the  formatted  version  of
        work.emptyCell.  (For  the  condition whether entries in mainFormatted
        can   be  bound,  see  below  in  the  description  of  the  component
        cacheEntries.)
  
  cacheEntries
        describes  whether  formatted  values  of  the entries in the matrices
        given by the components corner, labelsCol, labelsRow, main, and of the
        corresponding  row  and  column  separators  shall  be  stored  in the
        components  cornerFormatted,  labelsColFormatted,  labelsRowFormatted,
        and  mainFormatted. The value must be a Boolean, the default is false;
        it should be set to true only if the tables are reasonably small.
  
  cornerFormatted
        is  a  list  of lists of formatted entries corresponding to the corner
        component.  Each  entry  is  either  an  attribute  line  or a list of
        attribute  lines  (with  the same number of displayed characters), the
        values    can    be    computed    from    the   input   format   with
        BrowseData.FormattedEntry.  The  entries  are stored in this component
        only  if the component cacheEntries has the value true. The default is
        an empty list.
  
  labelsColFormatted
        corresponds to labelsCol in the same way as cornerFormatted to corner.
  
  labelsRowFormatted
        corresponds to labelsRow in the same way as cornerFormatted to corner.
  
  mainFormatted
        corresponds to main in the same way as cornerFormatted to corner.
  
  m0
        is  the  maximal  number  of  rows in the column labels table. If this
        value  is not bound then it is computed from the components corner and
        labelsCol.
  
  n0
        is the maximal number of columns in corner and labelsRow.
  
  m
        is  the  maximal number of rows in labelsRow and main. This value must
        be  set  in  advance  if  the values of main are computed using a Main
        function,  and  if  the  number of rows in main is larger than that in
        labelsRow.
  
  n
        is  the  maximal  number  of columns in labelsCol and main. This value
        must be set in advance if the values of main are computed using a Main
        function,  and if the number of columns in main is larger than that in
        labelsCol.
  
  heightLabelsCol
        is  a list of 2 m0+ 1 nonnegative integers, the entry at position i is
        the  maximal  height of the entries in the i-th row of cornerFormatted
        and  labelsColFormatted.  Values  that  are  not bound are computed on
        demand     from    the    table    entries,    with    the    function
        BrowseData.HeightLabelsCol.  (So  if  one  knows the needed heights in
        advance,  it  is  advisable  to set the values, in order to avoid that
        formatted  table  entries are computed just for computing their size.)
        The default is an empty list.
  
  widthLabelsRow
        is  the  corresponding  list  of  2 n0+ 1 maximal widths of entries in
        cornerFormatted and labelsRowFormatted.
  
  heightRow
        is  the  corresponding  list  of  2 m+ 1 maximal heights of entries in
        labelsRowFormatted and mainFormatted.
  
  widthCol
        is  the  corresponding  list  of  2  n+ 1 maximal widths of entries in
        labelsColFormatted and mainFormatted.
  
  emptyCell
        is  a  table  cell  data  object to be used as the default for unbound
        positions in the four matrices. The default is the empty list.
  
  sepCategories
        is  an  attribute  line  to  be  used  repeatedly as a separator below
        expanded category rows. The default is the string "-".
  
  startCollapsedCategory
        is  a  list  of attribute lines to be used as prefixes of unhidden but
        collapsed  category rows. For category rows of level i, the last bound
        entry  before  the (i+1)-th position is used. The default is a list of
        length  one,  the entry is the boldface variant of the string "> ", so
        collapsed category rows on different levels are treated equally.
  
  startExpandedCategory
        is  a  list  of  attribute  lines  to  be used as prefixes of expanded
        category rows, analogously to startCollapsedCategory. The default is a
        list of length one, the entry is the boldface variant of the string "*
        ", so expanded category rows on different levels are treated equally.
  
  startSelect
        is  an  attribute  line  to be used as a prefix of each attribute line
        that  belongs  to  a  selected  cell.  The  default  is  to switch the
        attribute NCurses.attrs.STANDOUT on, see Section 2.1-7.
  
  Click
        is  a record whose component names are names of available modes of the
        browse  table.  The  values  are  unary functions that take the browse
        table  as  their  argument.  If  the  action Click is available in the
        current  mode and the corresponding input is entered then the function
        in the relevant component of the Click record is called.
  
  availableModes
        is a list whose entries are the mode records that can be used when one
        navigates through the browse table, see Section 5.2.
  
  SpecialGrid
        is a function that takes a browse table and a record as its arguments.
        It  is  called  by BrowseData.ShowTables after the current contents of
        the window has been computed, and it is intended to draw an individual
        grid  into  the  table  that  fits  better  than  anything that can be
        specified  in  terms of row and column separators. (If other functions
        than BrowseData.ShowTables are used in some modes of the browse table,
        these functions must deal with this aspect themselves.) The default is
        to do nothing.
  
  The following components are provided in BrowseData.defaults.dynamic.
  
  changed
        is  a  Boolean that must be set to true by action functions whenever a
        refresh of the window is necessary; it is automatically reset to false
        after the refresh.
  
  indexRow
        is  a  list of positive integers. The entry k at position i means that
        the k-th row in the mainFormatted table is shown as the i-th row. Note
        that  depending on the current status of the browse table, the rows of
        mainFormatted  (and  of  main)  may be permuted, or it may even happen
        that  a row in mainFormatted is shown several times, for example under
        different category rows. It is assumed (as a sort convention) that the
        even  positions  in  indexRow  point  to  even  numbers,  and that the
        subsequent  odd  positions (corresponding to the following separators)
        point  to  the subsequent odd numbers. The default value is the list [
        1,  2,  ...,  m  ],  where  m  is  the number of rows in mainFormatted
        (including the separator rows, so m is always odd).
  
  indexCol
        is the analogous list of positive integers that refers to columns.
  
  topleft
        is  a  list  of  four  positive  integers denoting the current topleft
        position  of  the  main table. The value [ i, j, k, l ] means that the
        topleft entry is indexed by the i-th entry in indexRow, the j-th entry
        in indexCol, and the k-th row and l-th column inside the corresponding
        cell. The default is [ 1, 1, 1, 1 ].
  
  isCollapsedRow
        is  a  list  of Booleans, of the same length as the indexRow value. If
        the  entry  at  position  i is true then the i-th row is currently not
        shown  because  it  belongs to a collapsed category row. It is assumed
        (as  a hide convention) that the value at any even position equals the
        value  at the subsequent odd position. The default is that all entries
        are false.
  
  isCollapsedCol
        is the corresponding list for indexCol.
  
  isRejectedRow
        is  a  list  of  Booleans. If the entry at position i is true then the
        i-th  row is currently not shown because it does not match the current
        filtering  of  the table. Defaults, length, and hide convention are as
        for isCollapsedRow.
  
  isRejectedCol
        is the corresponding list for indexCol.
  
  isRejectedLabelsRow
        is  a  list  of  Booleans. If the entry at position i is true then the
        i-th column of row labels is currently not shown.
  
  isRejectedLabelsCol
        is the corresponding list for the column labels.
  
  activeModes
        is  a  list  of  mode records that are contained in the availableModes
        list  of  the  work component of the browse table. The current mode is
        the  last  entry in this list. The default depends on the application,
        BrowseData.defaults  prescribes the list containing only the mode with
        name component "browse".
  
  selectedEntry
        is  a  list  [  i,  j  ]. If i = j = 0 then no table cell is selected,
        otherwise  i  and j are the row and column index of the selected cell.
        (Note that i and j are always even.) The default is [ 0, 0 ].
  
  selectedCategory
        is  a  list  [  i, l ]. If i = l = 0 then no category row is selected,
        otherwise  i  and  l  are  the row index and the level of the selected
        category row. (Note that i is always even.) The default is [ 0, 0 ].
  
  searchString
        is  the  last string for which the user has searched in the table. The
        default is the empty string.
  
  searchParameters
        is   a   list   of  parameters  that  are  modified  by  the  function
        BrowseData.SearchStringWithStartParameters.    If   one   sets   these
        parameters  in  a  search  then  these values hold also for subsequent
        searches.  So  it  may  make sense to set the parameters to personally
        preferred ones.
  
  sortFunctionForColumnsDefault
        is  a  function  with two arguments used to compare two entries in the
        same  column  of  the  main  table  (or  two category row values). The
        default  is  the  operation  \<.  (Note  that  this default may be not
        meaningful if some of the rows or columns contain strings representing
        numbers.)
  
  sortFunctionForRowsDefault
        is the analogous function for comparing two entries in the same row of
        the main table.
  
  sortFunctionsForRows
        is  a list of comparison functions, if the i-th entry is bound then it
        replaces the sortFunctionForRowsDefault value when the table is sorted
        w.r.t. the i-th row.
  
  sortFunctionsForColumns
        is  the  analogous  list  of  functions for the case that the table is
        sorted w.r.t. columns.
  
  sortParametersForRowsDefault
        is  a  list of parameters for sorting the main table w.r.t. entries in
        given rows, e. g., whether one wants to sort ascending or descending.
  
  sortParametersForColumnsDefault
        is  the analogous list of parameters for sorting w.r.t. given columns.
        In  addition  to  the  parameters for rows, also parameters concerning
        category  rows are available, e. g., whether the data columns that are
        transformed into category rows shall be hidden afterwards or not.
  
  sortParametersForRows
        is  a list that contains ar position i, if bound, a list of parameters
        that  shall  replace  those  in  sortParametersForRowsDefault when the
        table is sorted w.r.t. the i-th row.
  
  sortParametersForColumns
        is the analogous list of parameters lists for sorting w.r.t. columns.
  
  categories
        describes  the  current category rows. The value is a list [ l_1, l_2,
        l_3  ]  where  l_1 is a sorted list [ i_1, i_2, ..., i_k ] of positive
        integers,  l_2  is a list of length k where the j-th entry is a record
        with  the  components  pos  (with  value i_j), level (the level of the
        category  row),  value (an attribute line to be shown), separator (the
        separator  below  this  category  row is a repetition of this string),
        isUnderCollapsedCategory (true if the category row is hidden because a
        category  row  of  an outer level is collapsed; note that in the false
        case,  the  category  row itself can be collapsed), isRejectedCategory
        (true  if  the  category  row  is hidden because none of th edata rows
        below  this  category  match  the current filtering of the table); the
        list l_3 contains the levels for which the category rows shall include
        the  numbers of data rows under these category rows. The default value
        is  [ [], [], [] ]. (Note that this hide convention makes sense mainly
        if  together  with  a  hidden  category row, also the category rows on
        higher  levels  and  the  corresponding data rows are hidden –but this
        property  is  not  checked.)  Category  rows  are  computed  with  the
        CategoryValues function in the work component of the browse table.
  
  log
        describes  the  session log which is currently written. The value is a
        list of positive integers, representing the user inputs in the current
        session.  When  GAP  returns  from  a  call  to  NCurses.BrowseGeneric
        (4.3-1),  one  can access the log list of the user interactions in the
        browse table as the value of its component dynamic.log.
  
        If    BrowseData.logStore    had    been    set    to    true   before
        NCurses.BrowseGeneric  (4.3-1)  had been called then the list can also
        be  accessed as the value of BrowseData.log. If BrowseData.logStore is
        unbound  or has a value different from true then BrowseData.log is not
        written.  (This  can  be  interesting  in  the  case  of  browse table
        applications  where  the  user does not get access to the browse table
        itself.)
  
  replay
        describes  the non-interactive input for the current browse table. The
        value  is  a record with the components logs (a dense list of records,
        the  default  is  an  empty list) and pointer (a positive integer, the
        default  is  1).  If  pointer is a position in logs then currently the
        pointer-th  record  is  processed,  otherwise  the  browse  table  has
        exhausted  its  non-interactive  part, and requires interactive input.
        The  records  in log have the components steps (a list of user inputs,
        the  default  is an empty list), position (a positive integer denoting
        the  current  position  in  the  steps  list  if  the log is currently
        processed,  the default is 1), replayInterval (the timeout between two
        steps  in milliseconds if the log is processed, the default is 0), and
        quiet  (a  Boolean, true if the steps shall not be shown on the screen
        until the end of the log is reached, the default is false).
  
  5.4-2 BrowseData.SetReplay
  
  BrowseData.SetReplay( data )  function
  
  This      function      sets      and      resets      the      value     of
  BrowseData.defaults.dynamic.replay.
  
  When  BrowseData.SetReplay  is  called with a list data as its argument then
  the entries are assumed to describe user inputs for a browse table for which
  NCurses.BrowseGeneric (4.3-1) will be called afterwards, such that replay of
  the  inputs  runs.  (Valid  input  lists  can be obtained from the component
  dynamic.log of the browse table in question.)
  
  When  BrowseData.SetReplay  is  called  with  the  only  argument false, the
  component   is   unbound   (so   replay  is  disabled,  and  thus  calls  to
  NCurses.BrowseGeneric (4.3-1) will require interactive user input).
  
  The  replay feature should be used by initially setting the input list, then
  running  the  replay  (perhaps  several  times),  and  finally unbinding the
  inputs,  such that subsequent uses of other browse tables do not erroneously
  expect their input in BrowseData.defaults.dynamic.replay.
  
  Note  that the value of BrowseData.defaults.dynamic.replay is used in a call
  to  NCurses.BrowseGeneric  (4.3-1) only if the browse table in question does
  not have a component dynamic.replay before the call.
  
  5.4-3 BrowseData.AlertWithReplay
  
  BrowseData.AlertWithReplay( t, messages[, attrs] )  function
  Returns:  an integer representing a (simulated) user input.
  
  The  function  BrowseData.AlertWithReplay  is  a  variant  of  NCurses.Alert
  (3.1-1)  that  is  adapted for the replay feature of the browse table t, see
  Section  4.1.  The  arguments  messages  and  attrs  are  the  same  as  the
  corresponding  arguments  of  NCurses.Alert (3.1-1), the argument timeout of
  NCurses.Alert  (3.1-1)  is  taken  from  the  browse table t, as follows. If
  BrowseData.IsDoneReplay  returns  true for t then timeout is zero, so a user
  input  is requested for closing the alert box; otherwise the requested input
  character is fetched from t.dynamic.replay.
  
  If  timeout  is  zero  and  mouse  events  are enabled (see NCurses.UseMouse
  (2.2-10)) then the box can be moved inside the window via mouse events.
  
  No  alert box is shown if BrowseData.IsQuietSession returns true when called
  with  t.dynamic.replay, otherwise the alert box is closed after the time (in
  milliseconds) that is given by the replayInterval value of the current entry
  in t.dynamic.replay.logs.
  
  The  function  returns  either the return value of the call to NCurses.Alert
  (3.1-1)  (in  the  interactive  case) or the value that was fetched from the
  current replay record (in the replay case).
  
  5.4-4 BrowseData.actions.ShowHelp
  
  BrowseData.actions.ShowHelp global variable
  
  There  are  two  predefined  ways  for showing an overview of the admissible
  inputs and their meaning in the current mode of a browse table. The function
  BrowseData.ShowHelpTable displays this overview in a browse table (using the
  help mode), and BrowseData.ShowHelpPager uses NCurses.Pager.
  
  Technically,  the  only  difference  between  these  two  functions  is that
  BrowseData.ShowHelpTable      supports     the     replay     feature     of
  NCurses.BrowseGeneric  (4.3-1), whereas BrowseData.ShowHelpPager simply does
  not call the pager in replay situations.
  
  The  action  record  BrowseData.actions.ShowHelp is associated with the user
  inputs  ?  or F1 in standard NCurses.BrowseGeneric (4.3-1) applications, and
  it  is  recommended  to  do  the same in other NCurses.BrowseGeneric (4.3-1)
  applications.  This  action  calls  the  function  stored  in  the component
  work.ShowHelp  of  the  browse  table,  the  default  (i. e.,  the  value of
  BrowseData.defaults.work.ShowHelp) is BrowseData.ShowHelpTable.
  
    Example  
    gap> xpl1.work.ShowHelp:= BrowseData.ShowHelpPager;;
    gap> BrowseData.SetReplay( "?Q" );
    gap> Unbind( xpl1.dynamic );
    gap> NCurses.BrowseGeneric( xpl1 );
    gap> xpl1.work.ShowHelp:= BrowseData.ShowHelpTable;;
    gap> BrowseData.SetReplay( "?dQQ" );
    gap> Unbind( xpl1.dynamic );
    gap> NCurses.BrowseGeneric( xpl1 );
    gap> BrowseData.SetReplay( false );
    gap> Unbind( xpl1.dynamic );
  
  
  5.4-5 BrowseData.actions.SaveWindow
  
  BrowseData.actions.SaveWindow global variable
  
  The function BrowseData.actions.SaveWindow.action asks the user to enter the
  name  of  a  global  GAP variable, using NCurses.GetLineFromUser (3.1-3). If
  this  variable  name  is valid and if no value is bound to this variable yet
  then the current contents of the window of the browse table that is given as
  the argument is saved in this variable, using NCurses.SaveWin (2.2-11).
  
  5.4-6 BrowseData.actions.QuitMode
  
  BrowseData.actions.QuitMode global variable
  BrowseData.actions.QuitTable global variable
  
  The  function BrowseData.actions.QuitMode.action unbinds the current mode in
  the  browse  table  that  is given as its argument (see Section 5.2), so the
  browse  table  returns  to the mode from which this mode had been called. If
  the  current  mode is the only one, first the user is asked for confirmation
  whether  she  really  wants to quit the table; only if the y key is hit, the
  last mode is unbound.
  
  The  function  BrowseData.actions.QuitTable.action  unbinds all modes in the
  browse table that is given as its argument, without asking for confirmation;
  the effect is to exit the browse application (see Section 5.3).
  
  5.4-7 BrowseData.actions.Error
  
  BrowseData.actions.Error global variable
  
  After NCurses.BrowseGeneric (4.3-1) has been called, interrupting by hitting
  the  Ctrl-C  keys  is  not possible. It is recommended to provide the action
  BrowseData.actions.Error  for  each  mode of a NCurses.BrowseGeneric (4.3-1)
  application,  which  enters  a  break  loop  and  admits  returning  to  the
  application. The recommended user input for this action is the E key.