eshell: how to alias cp 'cp -i' ?

[furue]

Hello,

I'm new to eshell and am wondering how to alias
"cp" to "cp -i".  As a first step, I tried this:

  ~ $ alias tmpcp 'cp -i'
  ~ $ tmpcp tmp.eps tmp2.eps
  cp: missing destination file or directory
  ~ $

I don't find a/the documentation (the info page
on the eshell alias is empty on my system, which
is emacs22 on the testing distribution of Debian),
or I fail to find a solution in the archive of this group
(the lastest posting which is more or less relevent
is dated 2001 or so).

I don't insist on aliases.  Something like

    (defun cp (args)  (builtin-cp -i args))

would do, too.  (I'm a lisp newbie, too, so
I'm sure that the code above is wrong.)

Thank you,
Ryo