I don't think monkey patching is required. Although without a dedicated interpreter, you can just do what sbcl does under the hood and maintain what is essentia

I don't think monkey patching is required. Although without a dedicated interpreter, you can just do what sbcl does under the hood and maintain what is essentially a tempfile and keep compiling that and reporting the output for every new line/block of code. (I don't know how sbcl actually works, being a lisp I presume it doesn't actually use a tempfile but instead a list in memory of the code the user submitted and then invokes the compiler as needed for new input including the output state as available symbols.) A cycle that went something like: 1. Write the line to a file 2. Compile file with default flags 3. Run binary in gdb causing gdb to dump certain interest info (stack info, variable contents, etc) 4. Read the sections/symbols and merge this data into the gdb data (maybe get it from gdb) 5. Dump this data into your reply and refresh waiting for user input. You could have a few basic commands in the repl: Modify the compiler args Add/remove/edit a line Attach gdb. Emacs or vim could easily do this, and I suspect there are people who already do almost exactly this. You could also just use any editor/ide with debug integration and keep a scratch file around...