JEL (Java Expressions Library) is a library for evaluating simple single-line expressions in Java. The key feature of JEL is the fact that it is a compiler. The language of JEL expressions resembles the Java Language expressions as close as possible. JEL supports all Java primitive types and classes (even in the form of constants), allows one to call both static and virtual methods of Java classes (with no additinal runtime costs and no wrappers), and performs evaluation of constant subexpressions at a compile time.
yacts, yet another continuous time simulator, uses J+ to interpret scripts, defining systems of ordinary differential equations, which it solves. J+ is a functional non-imperative simulation language with lazy evaluation, based on the J programming language, a dialect of APL. A program in J+ is a collection of (possibly functional) J assignment statements, just like a set of formulae on a sheet of paper. The interpreter, implemented as a software library, knows the interdependencies between these formulae and is able to compute any of the defined quantities with minimal effort, keeping track of the values which were already computed. The driver program (such as yacts) may ask the interpreter to compute certain quantities and set the values for others (propagating the changes to dependents).