I should have expanded on the 'not strictly true' bit: for a while I wrote code on Sublime Text and used the REPL from SLIME, with the windows side by side, as

I should have expanded on the 'not strictly true' bit: for a while I wrote code on Sublime Text and used the REPL from SLIME, with the windows side by side, as SublimeREPL was pretty terrible. And I was fairly productive, too. Eventually I just caved and learned Emacs.