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 ACHOICE()
 Execute a pop-up menu
------------------------------------------------------------------------------
 Syntax

     ACHOICE(<nTop>, <nLeft>, <nBottom>, <nRight>,
        <acMenuItems>,
        [<alSelectableItems> | <lSelectableItems>],
        [<cUserFunction>],
        [<nInitialItem>],
        [<nWindowRow>]) --> nPosition

 Arguments

     <nTop>, <nLeft> and <nBottom>, <nRight> are the upper left and lower
     right window coordinates.  Row values can range from zero to MAXROW()
     and column values can range from zero to MAXCOL().

     <acMenuItems> is an array of character strings to display as the
     menu items.  The individual menu items are later identified by their
     numeric positions in this array.

     <alSelectableItems> is a parallel array of logical values--one
     element for each item in <acMenuItems>--that specify the selectable menu
     items.  Elements can be logical values or character strings.  ACHOICE()
     will not permit a null string and stops displaying if it encounters one.
     If the element is a character string, it is evaluated as a macro
     expression which should evaluate to a logical data type.  In either
     case, a value of false (.F.) means that the corresponding menu item is
     not available, and a value of true (.T.) means that it is available.  If
     you specify <lSelectableItems> instead of an array, false (.F.) makes
     all menu items unavailable and true (.T.) makes all menu items
     available.  By default, all menu items are available for selection.

     <cUserFunction> is the name of a user-defined function that executes
     when an unrecognizable key is pressed.  Specify the function name as a
     character expression without parentheses or arguments.  Note that the
     behavior of ACHOICE() is affected by the presence of this argument.
     Refer to the discussion below for further information.

     <nInitialItem> is the position in the <acMenuItems> array of the
     item that will be highlighted when the menu is initially displayed.  If
     you specify an unavailable menu item or no argument at all, the initial
     menu item is the first selectable item in the array.

     <nWindowRow> is the window row number on which the initial menu item
     will appear.  Row numbering begins with zero.  By default, the initial
     menu item appears as close to the top of the window as possible, without
     leaving any empty rows at the bottom.  Thus, if there are enough menu
     items following the initial one to fill up the window, the initial form
     will appear on the first row (row zero) of the menu.  This function
     argument is used to control the initial menu appearance when there are
     more menu items than will fit in the window.

     As with all functions, optional arguments are omitted by using a comma
     instead of the actual argument.

 Returns

     ACHOICE() returns the numeric position in the <acMenuItems> array of the
     menu item selected.  If the selection process is aborted, ACHOICE()
     returns zero.

 Description

     ACHOICE() is a user interface function that can create various kinds of
     pop-up menus.  Each menu uses an array of character strings as menu
     items and a parallel array of logical values to determine whether items
     are selectable.  When you invoke ACHOICE(), the list of menu items is
     displayed within the specified window coordinates.  When the user
     presses Return, the current item is selected, and ACHOICE() returns the
     position of the menu item in <acMenuItems>.  When the user presses Esc,
     ACHOICE() aborts and returns zero.

     The menu items scroll if the number of items in <acMenuItems> exceeds
     the number of rows in the menu window, and the user attempts to move the
     highlight beyond the top or bottom of the menu window.  Note that the
     highlight does not wrap when you reach the top or bottom of the list of
     items.  Pressing the first letter does, however, wrap the highlight
     within the set of items whose first letter matches the key you press.

     .  Navigating the menu: ACHOICE() has two modes depending on
        whether the <cUserFunction> argument is specified.  If it is not
        specified the following navigation keys are active:

        ACHOICE() Keys (No User Function)
        ---------------------------------------------------------------------
        Key            Action
        ---------------------------------------------------------------------
        Uparrow        Go to previous item
        Dnarrow        Go to next item
        Home           Go to first item in menu
        End            Go to last item in menu
        Ctrl-Home      Go to first item in window
        Ctrl-End       Go to last item in window
        PgUp           Go to previous page
        PgDn           Go to next page
        Ctrl-PgUp      Go to the first item in menu
        Ctrl-PgDn      Go to last item in menu
        Return         Select current item
        Esc            Abort selection
        Leftarrow      Abort selection
        Rightarrow     Abort selection
        First Letter   Go to next item beginning with first letter
        ---------------------------------------------------------------------

     .  Color: Menu items are displayed in standard color, the
        highlight in enhanced color, and the unavailable items in the
        unselected color.  For example, the following color statement:

        SETCOLOR("W+/N, BG+/B, , , W/N")

        displays a menu that is bright white on black, the highlight is
        bright cyan on blue, and the unavailable menu items are dim white on
        black.

     .  User function: Like the other user interface functions,
        ACHOICE() supports a user function.  The user function is specified
        when you want to nest ACHOICE() invocations to create hierarchical
        menus or to redefine keys.

        When a user function is specified, ACHOICE() processes only a limited
        set of keys automatically.  These are listed in the table below.  All
        other keys generate a key exception which passes control to the user
        function for handling.  Control is also passed to the user function
        when ACHOICE() goes idle (i.e., when there are no more keys to
        process).

        ACHOICE() Keys (User Function Specified)
        ---------------------------------------------------------------------
        Key            Action
        ---------------------------------------------------------------------
        Uparrow        Go to previous item
        Dnarrow        Go to next item
        Ctrl-Home      Go to first item in window
        Ctrl-End       Go to last item in window
        PgUp           Go to previous page
        PgDn           Go to next page
        Ctrl-PgUp      Go to the first item in menu
        Ctrl-PgDn      Go to last item in menu
        ---------------------------------------------------------------------

        When ACHOICE() executes the user function, it automatically passes
        the following three parameters:

        -  The current ACHOICE() mode

        -  The current element in the array of items

        -  The relative row position within the menu window

        The mode indicates the current state of ACHOICE() depending on the
        key pressed and the action taken by ACHOICE() prior to executing the
        user function.  The mode parameter has the following possible values:

        ACHOICE() Modes
        ---------------------------------------------------------------------
        Mode    Achoice.ch     Description
        ---------------------------------------------------------------------
        0       AC_IDLE        Idle
        1       AC_HITTOP      Attempt to cursor past top of list
        2       AC_HITBOTTOM   Attempt to cursor past bottom of list
        3       AC_EXCEPT      Keystroke exceptions
        4       AC_NOITEM      No selectable items
        ---------------------------------------------------------------------

        After the user function has performed whatever operations are
        appropriate to the ACHOICE() mode or LASTKEY(), it must RETURN a
        value requesting ACHOICE() to perform an operation from the following
        set of actions:

        ACHOICE() User Function Return Values
        ---------------------------------------------------------------------
        Value   Achoice.ch     Action
        ---------------------------------------------------------------------
        0       AC_ABORT       Abort selection
        1       AC_SELECT      Make selection
        2       AC_CONT        Continue ACHOICE()
        3       AC_GOTO        Go to the next item whose first character
                               matches the key pressed
        ---------------------------------------------------------------------

 Examples

     .  This example uses two literal arrays to specify the menu items
        and selection criteria.  After the menu is displayed and the user
        makes a selection, the name of the selected menu item is displayed:

        acMenuItems := {"One", "Two", "-------", "Three"}
        alSelectableItems := {.T., .T., .F., .T.}
        nPosition := ACHOICE(10, 10, 12, 15, acMenuItems,;
                             alSelectableItems)
        ? acMenuItems[nPosition]

     .  This example declares an array of menu items and supplies a
        user-defined function which displays a message with each highlighted
        choice:

        #include "achoice.ch"
        #include "inkey.ch"

        PROCEDURE Main()

           LOCAL acMenuItems[4], cUserFunction, nRetVal
           LOCAL nKey, nPos

           acMenuItems[1] := "Add"
           acMenuItems[2] := "Edit"
           acMenuItems[3] := "Delete"
           acMenuItems[4] := "Update"

           CLS

           nPos := ACHOICE( 10, 10, 13, 15, acMenuItems,;
                           .T., "cUserFunction" )
           DO CASE
           CASE nPos == 1
              //  Put ADD routine here
           CASE nPos == 2
              //  Put EDIT routine here
           CASE nPos == 3
              //  Put DELETE routine here
           CASE nPos ==4
              //  Put UPDATE routine here
           ENDCASE

        RETURN


        FUNCTION cUserFunction( nMode, nCurElement, nRowPos )

           LOCAL nRetVal := AC_CONT     // Default, Continue
           LOCAL nKey := LASTKEY()

           DO CASE
        // After all pending keys are processed, display message
           CASE nMode == AC_IDLE
           DO CASE
              CASE nCurElement == 1
                 @ 22, 5 SAY " Adding   "
              CASE nCurElement == 2
                 @ 22, 5 SAY " Editing  "
              CASE nCurElement ==  3
                 @ 22, 5 SAY " Deleting "
              CASE nCurElement ==  4
                 @ 22, 5 SAY " Updating "
           ENDCASE

              nRetVal := AC_CONT            // Continue ACHOICE()

           CASE nMode == AC_HITTOP          // Attempt to go past Top
              TONE( 100, 3 )
           CASE nMode == AC_HITBOTTOM       // Attempt to go past
                                            // Bottom
              TONE( 100, 3 )

           CASE nMode == AC_EXCEPT          // Key Exception
              DO CASE
              CASE nKey == K_RETURN         // If RETURN key, select
                 nRetVal := AC_SELECT
              CASE nKey == K_ESC            // If ESCAPE key, abort
                 nRetVal := AC_ABORT
              OTHERWISE
                    nRetVal := AC_GOTO      // Otherwise, go to item
              ENDCASE
           ENDCASE

        RETURN nRetVal

     .  The next example declares the arrays, specifies a selection
        condition for one of the menu items, and supplies a user function:

        EXTERNAL UPDATED
        //
        FUNCTION MyMenu
           LOCAL acMenuItems[4], alSelectableItems[4],;
                  cUserFunction := "DoIt"
           //
           acMenuItems[1] := "Add Record"
           acMenuItems[2] := "Edit Record"
           acMenuItems[3] := "Delete Record"
           acMenuItems[4] := "Update Record"
           //
           alSelectableItems[1] := .T.
           alSelectableItems[2] := .T.
           alSelectableItems[3] := .T.
           alSelectableItems[4] := "!UPDATED()"
           // Selection condition

           RETURN ACHOICE(10, 10, 12, 15, acMenuItems,;
              alSelectableItems, cUserFunction)

     .  This example uses two arrays to specify menu items and
        corresponding action blocks.  After the menu is displayed and the
        user makes a selection, the ACHOICE() return value is used to
        determine which action block of the aActionItems array is evaluated:

        PROCEDURE Main()
           LOCAL nChoice
           LOCAL aMenuItems := { "Add Record   ", ;
                                 "Edit Record  ", ;
                                 "Delete Record", ;
                                 "Update Record"   }

           LOCAL aActionItems := { {|| AddFunc()  }, ;
                                   {|| EditFunc() }, ;
                                   {|| DelFunc()  }, ;
                                   {|| UpdFunc()  }  }

           nChoice := ACHOICE( 10, 10, 13, 22, aMenuItems )

           IF nChoice == 0
              QUIT      // ESCAPE was pressed
           ENDIF

           EVAL( aActionItems[nChoice] )

        RETURN

 Files:  Library is EXTEND.LIB, header files are Achoice.ch and Inkey.ch.