The C++ interactive interpreter cling is based on LLVM and its C++ frontend clang. It has replaced ROOT's C++ interpreter CINT. Its main advantages:

• Production-grade parser.
• Just-in-time compiler (JIT), allowing e.g. calls into libraries without wrappers.
• Modular C++ API from the ground up.
• Separate parser and execution engine.
• C++ 11... support through clang.

We have announced cling to the public in 2011. cling is in production use by CERN; bugs should be reported to the ROOT project here.

We offer binary snapshots for download. There are build instructions, both for a stand-alone version of cling and for cling as part of ROOT.

We even have doxygen documentation of cling's code.