Add string concatenation and comparison methods.
Add explicit cast for expressions that don’t return an object value.
Evaluate the condition inside the while condition block.
Allow the string methods to handle null arguments.
Work around the fact that the Boehm GC only supports a limited number of roots (512-2048, depending on the compilation mode).
Add a File class to the runtime, which implements (very) simple file I/O.
Add an example that runs a bubblesort on a load of strings.  This code would benefit from different triggers for compilation (e.g. if a method runs for a long time, compile it the second time, or compile inner loops even before the entire function is compiled) and from inline caching.