Clojure: Controlling run-away trains, onions, and exercise bikes. A normal Clojure REPL (or prompt) in a terminal window is by default a bit touchy about infinite seqs, deeply nested structures, and long-running operations. Any of these can cause your REPL to wander off into the weeds, busy spinning, perhaps printing pages of useless data, with the only apparent remedy being to press CTRL-C, which