interp is a multifunction calculator with control flow written in g++. The syntax is meant to agree with a small subset of g++. It is being developed as a front end extension language for biological mathematical modeling software.@refill It supports declaration of double and integer variables, @code{while}, @code{if} and compound statements, and double precision arithmetic expressions.@refill Interp requires you use libg++ (version 1.36.2 is known to work) flex and bison. It was developed and tested on a sequent symmetry. Reports of installation problems on other systems would be welcome.