SBCL is essentially a compiler-only implementation of Common Lisp. That is, for all but a few special cases, eval creates a lambda expression, calls compile on the lambda expression to create a compiled function, and then calls funcall on the resulting function object. A more traditional interpreter is also available on default builds; it is usually only called internally. This is explicitly allowed by the ANSI standard, but leads to some oddities; e.g. at default settings, functionp and compiled-function-p are equivalent, and they collapse into the same function when SBCL is built without the interpreter.
http://www.softwarepreservation.org/projects/LISP/maclisp_fa...
Just to add to the above, I like CCL because it gives nice compiler messages --sometimes it warns me about things SBCL won't notice.
https://franz.com/support/documentation/10.1/doc/debugging.h...
Also, it may not be necessary to master the most complicated machinery: compiling function by function gives lots of hints, and the very nice [log4cl](https://github.com/sharplispers/log4cl/) is handy.
Same thing. Franz is the company. Allegro Lisp is the product. Like "Apple Macintosh computer."
> But why is it 'high performant' compared to other implementations? Like say CMU CL(now SBCL).
Somewhat better compiler, but mainly lots of extra features (better debugging, graphics, better libraries).
> why would one use Clozure CL instead of SBCL?
I use CCL because 1) I like the IDE and 2) its compiler is fast so you can always compile everything essentially for free. In other CLs you have to choose between running in compiled or interpreted mode, and that can sometimes cause problems. CCL doesn't have an interpreter at all. It always compiles everything and that makes it easier to use.