The same thing happens with Maxima / gcl. Here is a workaround:
(%i1) :lisp(cl:tan 2.0);
-2.1850398632615189
Barton
-----maxima-bounces at math.utexas.edu wrote: -----
>To: maxima at math.utexas.edu
>From: Mario Rodriguez <biomates at telefonica.net>
>Sent by: maxima-bounces at math.utexas.edu
>Date: 08/13/2007 04:26AM
>Subject: Tangents at lisp level
>
>I get an error message when I want to compute tangents at lisp level,
>both in clisp and sbcl:
>
>(%i1) :lisp (cos 2.0)
>-0.4161468365471424
>(%i1) :lisp (sin 2.0)
>0.9092974268256817
>(%i1) :lisp (tan 2.0)
>Maxima encountered a Lisp error:
>
>
>EVAL: undefined function TAN
>
>Automatically continuing.
>To reenable the Lisp debugger set *debugger-hook* to nil.
>_______________________________________________
>Maxima mailing list
>Maxima at math.utexas.edu
>http://www.math.utexas.edu/mailman/listinfo/maxima