Math::Expr parses mathematical expressions into a tree structure.
The expressions may contain integers, real numbers, alphanumeric
variable names, alphanumeric function names and most other characters
might be used as operators. The operators can consist of multiple
characters.  The only limitation is that a variable or function
name may not start on a digit, and not all chars are accepted in
operation names.

WWW: http://search.cpan.org/dist/Math-Expr/