Swift:
Using an interactive shell (REPL)
How to:
Invoke REPL by opening a terminal and running swift. Type code directly and hit Enter to run it. Here’s a taste:
1> let greeting = "Hello, REPL!"
greeting: String = "Hello, REPL!"
2> print(greeting)
Hello, REPL!Exit with :quit or Control-D.
Deep Dive
REPL’s roots go way back to Lisp interpreters in the ’60s. Swift’s REPL sits atop LLVM, a powerful compiler framework, offering more than just basic interpretation—it’s a full-fledged tool with autocomplete, debugging, and more. REPL is great for learning or prototyping, but it’s not a standalone development environment. Some people prefer using Playgrounds in Xcode for a more graphical, file-based approach, while others stick to traditional script editing and running.
Under the hood, Swift’s REPL dynamically compiles code to machine language and executes it, which is why it’s relatively fast. It can also access any compiles Swift modules, or even C libraries, making it quite powerful. Note, though, not everything works perfectly in REPL; some Swift features, particularly those requiring complex project setups or storyboard files, won’t fly here.