A typical Common Lisp development and run time environment behaves like a complete operating system, with multiple threads of execution and the ability to load new code and redefine objects (functions, etc.) dynamically, i.e. without stopping and restarting the “machine.”

This “operating system” characteristic also makes CL significantly more flexible than other popular programming languages. Whereas some other languages, such as shell scripts or Perl CGI scripts, need to pipe data around, in CL all data manipulations can run interactively within one single process with a shared memory space.

Programming in CL is distinguished from programming in other languages due to its unique syntax and development mode. CL allows developers to make changes and test them immediately, in an incremental manner. In other languages, a developer must follow the “compile-link-run-test” cycle. These extra steps add minutes or hours to each cycle of development, and break the programmer’s thought process. Multiply these figures by days, weeks, and months — and the potential savings are phenomenal.