Per http://dev.clojure.org/display/design/Socket+Server+REPL, want to enhance repl to support "commands" useful for nested repls or for parallel tooling repls communicating over sockets (CLJ-1671).
Commands are defined as keywords in the "repl" namespace. The REPL will trap these after reading but before evaluation. Currently this is a closed set, but perhaps it could be open - the server socket repl could then install new ones if desired when repl is invoked.
:repl/quit - same as Ctrl-D but works in terminal environments where that's not feasible. Allows for backing out of a nested REPL.
:repl/push - push the current repl "state" (tbd what that is, but at least ns) to a stateful map in the runtime. Returns coordinates that can be used to retrieve it elsewhere
:repl/pull <coords> - retrieves the repl state defined by the coordinates
In the tooling scenario, it is expected that there are two repls - the client repl and the tooling repl. The tooling can send :repl/push over the client repl before startup and retrieve the coordinates (which don't change). Then the tooling repl can call :repl/pull at any time to retrieve the state of the client repl.