Here are some fairly straightforward modifications that can be made to your Jack compiler.
All of these mods are strictly extensions of the book specified Jack language. Jack programs that compile with the supplied JackCompiler will be compatible with your extended compiler, except for identifier name clashes with new keywords.
These projects are basically cookbook recipes if you wrote a recursive descent compiler following the modules and methods recommended in projects 10 and 11.
These projects require extensive changes to underlying objects like SymbolTable and VmWriter, multiple source code passes through multiple .jack files,
or the implementation may require some non-standard techniques to work around limitations in the VmEmulator.