IELM (Interactive Emacs Lisp Mode) is a nice mode that gives you an interactive Emacs Lisp shell (or a REPL if you prefer) that you can use for exploratory programming. You can start it by pressing M-x ielm. You'll be taken to a buffer named "*ielm*", where Emacs Lisp expressions you've entered will be evaluated on pressing the Return key. IELM offers some nice features like tab autocompletion of symbol names and the ability to span an expression over several lines.
IELM is bundled with Emacs by default. No additional setup is required.
Show eldoc in IELM
(defun my-ielm-mode-defaults () (turn-on-eldoc-mode)) (setq my-ielm-mode-hook 'my-ielm-mode-defaults) (add-hook 'ielm-mode-hook (lambda () (run-hooks 'my-ielm-mode-hook)))