Implementations
See the Category Common Lisp implementations.
Common Lisp is defined by a specification (like Ada and C) rather than by one implementation (like Perl before version 6). There are many implementations, and the standard details areas in which they may validly differ.
In addition, implementations tend to come with library packages, which provide functionality not covered in the standard. Free and open source software libraries have been created to support such features in a portable way, and are most notably found in the repositories of the Common-Lisp.net and Common Lisp Open Code Collection projects.
Common Lisp implementations may use any mix of native code compilation, byte code compilation or interpretation. Common Lisp has been designed to support incremental compilers, file compilers and block compilers. Standard declarations to optimize compilation (such as function inlining or type specialization) are proposed in the language specification. Most Common Lisp implementations compile source code to native machine code. Some implementations can create (optimized) stand-alone applications. Others compile to interpreted bytecode, which is less efficient than native code, but eases binary-code portability. There are also compilers that compile Common Lisp code to C code. The misconception that Lisp is a purely interpreted language is most likely because Lisp environments provide an interactive prompt and that code is compiled one-by-one, in an incremental way. With Common Lisp incremental compilation is widely used.
Some Unix-based implementations (CLISP, SBCL) can be used as a scripting language; that is, invoked by the system transparently in the way that a Perl or Unix shell interpreter is.
Read more about this topic: Common Lisp