Apple’s new programming language swift has a great playground but can also be run in LLDB as a read-eval-print-loop:
$ alias swift=/Applications/Xcode6-Beta.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/swift $ swift Welcome to Swift! Type :help for assistance. 1> let greeting = "Hello REPL!" greeting: String = "Hello REPL!" 2> println(greeting) Hello REPL!