SLIME is a third–party tool that integrates with Common Lisp; it isn’t part of the language. With most Common Lisp implementations you can just use the repl to call (inspect foo) to see what slots foo has and their values. It will probably be a little clunky since drilling down into the details might require you to type numbers at a prompt. Meanwhile SLIME presents the same information in a UI, so you can click on things (or type the numbers if you prefer).
It just happens that SLIME is a pretty well designed UI (the acronym stands for Superior Lisp Interaction Mode for Emacs, so I guess that was the goal). It’s miles ahead of what you get from most other languages, even C++, but most of what makes it so great comes from features that were already present in the language implementations. It also combines very well with other advanced Emacs packages such as Paredit.
Interestingly, SLIME is implemented as a network protocol to allow for remote debugging, so you can implement a new UI for it any way you want. I’ve never used it, but you might check out SLIMV instead. https://www.vim.org/scripts/script.php?script_id=2531
It just happens that SLIME is a pretty well designed UI (the acronym stands for Superior Lisp Interaction Mode for Emacs, so I guess that was the goal). It’s miles ahead of what you get from most other languages, even C++, but most of what makes it so great comes from features that were already present in the language implementations. It also combines very well with other advanced Emacs packages such as Paredit.
Interestingly, SLIME is implemented as a network protocol to allow for remote debugging, so you can implement a new UI for it any way you want. I’ve never used it, but you might check out SLIMV instead. https://www.vim.org/scripts/script.php?script_id=2531