January 21, 2007
Everybody knows you can evaluate elisp expressions in the scratch buffer, but a lot less people seem to be aware of ielm the interactive Emacs Lisp mode, this mode opens a sort of Emacs REPL that allows you to work with Emacs Lisp much in the same way you’d do at a Common Lisp REPL.
Another little known fact is that you can evaluate elisp expressions at the eshell prompt, just try typing (+ 12 9) and hitting return. Spiffy eh? But you’ll quickly run into eshell’s elisp limitations: it doesn’t correctly indent code so it’s not really useful for ‘real’ elisp hacking, ielm is much better suited for that purpose as it does corretly indent elisp code.