bug#21584: 25.0.50; Please add cl-constantly function from Common Lisp

[Mark Karpov <markkarpov@openmailbox.org>]

In Common Lisp there is ‘constantly’ function:

  http://www.lispworks.com/documentation/HyperSpec/Body/f_cons_1.htm

which creates new function without side-effects that takes any number of
arguments and always returns specified value.

For some reason ‘cl-lib’ doesn't provide ‘cl-constantly’, so I guess it
should exist in pure Emacs Lisp under different name. However, I
couldn't find such a function, so I ask you to tell me name of function
that word like ‘constantly’ in Emacs Lisp or add ‘cl-constantly’ in
‘cl-lib’ in Emacs 25.



In GNU Emacs 25.0.50.21 (x86_64-unknown-linux-gnu, GTK+ Version 3.16.7)
 of 2015-09-20
Repository revision: 6afe8168dde7780853003dea2fb9e3a8ba57e2ea
Windowing system distributor 'The X.Org Foundation', version 11.0.11702000
Configured features:
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NOTIFY ACL GNUTLS LIBXML2 FREETYPE M17N_FLT LIBOTF XFT ZLIB
TOOLKIT_SCROLL_BARS GTK3 X11

Important settings:
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Major mode: ελ

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Recent messages:
Saving file /home/mark/projects/programs/emacs-lisp/para/para.el...
Wrote /home/mark/projects/programs/emacs-lisp/para/para.el
Undo! [2 times]
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Saving file /home/mark/projects/programs/emacs-lisp/para/para.el...
Wrote /home/mark/projects/programs/emacs-lisp/para/para.el
Type "q" in help window to restore its previous buffer.
Mark set
uncompressing cl-extra.el.gz...done
Note: file is write protected

Load-path shadows:
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