but using the source itself as the target of function calls and loops is new to me This was standard practice on interpreters for 8-bit microcomputers; with on

but using the source itself as the target of function calls and loops is new to me This was standard practice on interpreters for 8-bit microcomputers; with only a 64K total address space, creating an AST first seems immensely wasteful, so you interpret from the source directly. I believe shells still do this when you run shell scripts; I know the DOS COMMAND.COM definitely does.