Accessing local variables during debugging

Any reasonably large program has to use local variables. It is quite common in the Lisp language family to also allow functions that exist only in a local scope. Scoping rules often allow compilers to optimize away parts of the local environment; doing that is good for performance, but sometimes inconvenient for debugging.

We present a debugging library for Common Lisp that ensures access to the local variables during debugging. To prevent the optimisations from removing access to these variables, we use code-walking macros to store references to the local variables (and functions) inside global variables.