Emacs: Evaluate Elisp Code

Here's ways to eval elisp code, roughly in order of usefulness:

Alt+x eval-last-sexp 【Ctrl+x Ctrl+e】

Eval lisp expression to the left of cursor.

Result is placed in Messages Buffer, and temporarily displayed at bottom.

Alt+x eval-region

Eval text selection.

Alt+x eval-buffer

Eval whole buffer.

Alt+x load-file

Eval a file. It prompts for a filename.

Alt+x eval-defun

Eval function definition the cursor is in. (the elisp code must be well-indended, otherwise emacs may have problem finding function.) [see Emacs: narrow-to-defun, eval-defun, bug]

Alt+x eval-expression

Prompts you to type a emacs lisp expression.

Emacs Lisp Command Line Interface (REPL)

Alt+x ielm to start emacs interactive emacs lisp shell.

I recommend working in a buffer instead of REPL.

Working in a buffer (sometimes called notebook inteface) allows you to use full editing power, and eval any expression, in any order, anytime, anywhere. [see Command Line Interface (REPL) vs Notebook Interface]