5. Cling is (also, but not only) REPL¶
A read-eval-print-loop (REPL) is an interactive programming environment that takes user inputs, executes them, and returns the result to the user. In order to enable interactivity in C++, Cling provides several extensions to the C++ language:
Defining functions in the global scope: Cling redefines expressions at a global level. C++ provides limited support for this, Cling possesses the necessary semantics to re-define code while the program is running, minimizing the impedance mismatch between the REPL and the C++ codebase, and allowing for a seamlessly interactive programing experience.
Allows for implementation of commands that provide information about the current state of the environment. e.g., has an Application Programming Interface (API) to provide information about the current state of the environment.
Error recovery: Cling has an efficient error recovery system which allows it to handle the errors made by the user without restarting or having to redo everything from the beginning.
Tight feedback loop: It provides feedback about the results of the developer’s choices that is both accurate and fast.
Facilitates debugging: The programmer can inspect the printed result before deciding what expression to provide for the next line of code.