maint: Use macros to begin/end C++ namespaces. * BaseControl.cc, BaseControl.h, ButtonControl.cc, ButtonControl.h, ButtonGroup.cc, ButtonGroup.h, Canvas.cc, Canvas.h, CheckBoxControl.cc, CheckBoxControl.h, Container.cc, Container.h, ContextMenu.cc, ContextMenu.h, EditControl.cc, EditControl.h, Figure.cc, Figure.h, FigureWindow.cc, FigureWindow.h, GLCanvas.cc, GLCanvas.h, GenericEventNotify.h, KeyMap.cc, KeyMap.h, ListBoxControl.cc, ListBoxControl.h, Logger.cc, Logger.h, Menu.cc, Menu.h, MenuContainer.h, Object.cc, Object.h, ObjectProxy.cc, ObjectProxy.h, Panel.cc, Panel.h, PopupMenuControl.cc, PopupMenuControl.h, PushButtonControl.cc, PushButtonControl.h, PushTool.cc, PushTool.h, QtHandlesUtils.cc, QtHandlesUtils.h, RadioButtonControl.cc, RadioButtonControl.h, SliderControl.cc, SliderControl.h, Table.cc, Table.h, TextControl.cc, TextControl.h, TextEdit.cc, TextEdit.h, ToggleButtonControl.cc, ToggleButtonControl.h, ToggleTool.cc, ToggleTool.h, ToolBar.cc, ToolBar.h, ToolBarButton.cc, ToolBarButton.h, annotation-dialog.cc, annotation-dialog.h, gl-select.cc, gl-select.h, qopengl-functions.h, qt-graphics-toolkit.cc, qt-graphics-toolkit.h, QTerminal.h, color-picker.cc, color-picker.h, command-widget.cc, command-widget.h, community-news.cc, community-news.h, dialog.cc, dialog.h, documentation-bookmarks.cc, documentation-bookmarks.h, documentation-dock-widget.cc, documentation-dock-widget.h, documentation.cc, documentation.h, dw-main-window.cc, dw-main-window.h, external-editor-interface.cc, external-editor-interface.h, files-dock-widget.cc, files-dock-widget.h, find-files-dialog.cc, find-files-dialog.h, find-files-model.cc, find-files-model.h, graphics-init.cc, graphics-init.h, gui-settings.cc, gui-settings.h, gui-utils.cc, gui-utils.h, history-dock-widget.cc, history-dock-widget.h, interpreter-qobject.cc, interpreter-qobject.h, led-indicator.cc, led-indicator.h, file-editor-interface.h, file-editor-tab.cc, file-editor-tab.h, file-editor.cc, file-editor.h, find-dialog.cc, find-dialog.h, marker.cc, marker.h, octave-qscintilla.cc, octave-qscintilla.h, octave-txt-lexer.cc, octave-txt-lexer.h, main-window.cc, main-window.h, news-reader.cc, news-reader.h, octave-dock-widget.cc, octave-dock-widget.h, octave-qobject.cc, octave-qobject.h, qt-application.cc, qt-application.h, qt-interpreter-events.cc, qt-interpreter-events.h, qt-utils.h, release-notes.cc, release-notes.h, resource-manager.cc, resource-manager.h, set-path-dialog.cc, set-path-dialog.h, set-path-model.cc, set-path-model.h, settings-dialog.cc, settings-dialog.h, shortcut-manager.cc, shortcut-manager.h, tab-bar.cc, tab-bar.h, terminal-dock-widget.cc, terminal-dock-widget.h, variable-editor-model.cc, variable-editor-model.h, variable-editor.cc, variable-editor.h, welcome-wizard.cc, welcome-wizard.h, workspace-model.cc, workspace-model.h, workspace-view.cc, workspace-view.h: Use new macros to begin/end C++ namespaces.

########################################################################
##
## Copyright (C) 2012-2022 The Octave Project Developers
##
## See the file COPYRIGHT.md in the top-level directory of this
## distribution or <https://octave.org/copyright/>.
##
## This file is part of Octave.
##
## Octave is free software: you can redistribute it and/or modify it
## under the terms of the GNU General Public License as published by
## the Free Software Foundation, either version 3 of the License, or
## (at your option) any later version.
##
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## WITHOUT ANY WARRANTY; without even the implied warranty of
## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
## GNU General Public License for more details.
##
## You should have received a copy of the GNU General Public License
## along with Octave; see the file COPYING.  If not, see
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########################################################################

%!test <*31371>
%! % Work around MATLAB bug where f(x)(y) is invalid syntax
%! % (This bug does not apply to Octave)
%!
%! C = @(fcn,x) fcn(x);
%! C2 = @(fcn,x,y) fcn(x,y);
%!
%! % Church Booleans
%! T = @(t,f) t;
%! F = @(t,f) f;
%!
%! % Church Numerals
%! Zero  = @(fcn,x) x;
%! One   = @(fcn,x) fcn(x);
%! Two   = @(fcn,x) fcn(fcn(x));
%! Three = @(fcn,x) fcn(fcn(fcn(x)));
%! Four  = @(fcn,x) fcn(fcn(fcn(fcn(x))));
%!
%! % Arithmetic Operations
%! Inc = @(a) @(f,x) f(a(f,x)); % Increment
%! Add = @(a,b) @(f,x) a(f,b(f,x));
%! Mult = @(a,b) @(f,x) a(@(x) b(f,x),x);
%! Dec = @(a) @(f,x) C(a(@(g) @(h) h(g(f)), @(u) x), @(u) u); % Decrement
%! Sub = @(a,b) b(Dec, a);
%!
%! % Renderer - Convert church numeral to "real" number
%! Render = @(n) n(@(n) n+1,0);
%!
%! % Predicates
%! Iszero = @(n) n(@(x) F, T);
%!
%! % Y combinator implements recursion
%! Ycomb = @(f) C(@(g) f(@(x) C(g(g), x)), ...
%!                @(g) f(@(x) C(g(g), x)));
%!
%! Factorial = Ycomb(@(f) @(n) C(C2(Iszero(n), ...
%!                   @(d) One, @(d) Mult(n, f(Dec(n)))),0));
%!
%! assert (Render (Factorial (Two)), 2);
%! assert (Render (Factorial (Three)), 6);
%! assert (Render (Factorial (Four)), 24);