Introducing cling, a C++ Interpreter Based on clang/LLVM

Google Tech Talk
March 15, 2012

Presented by Axel Naumann, CERN.

ABSTRACT

At CERN, 50 million lines of C++ code are being used by about 10 thousand physicist. Many of them are not programming experts. To make writing C++ more accessible, ROOT (http://root.cern.ch), one of the core tools at CERN, has been using the CINT C++ interpreter for more than 15 years. CINT also opens up a whole new world of dynamic programming: plug-ins, signal/slot, runtime evaluation, reflection. In particular, the latter is fundamental to CERN and its petabytes of Large Hadron Collider data per year, which are created, serialized, and analyzed as C++ objects.

Given the complexity of writing C++, Python is widely used to interface and steer C++ components. Using a SWIG-like approach to interfacing C++ and Python does not scale to CERN's context. I will present our completely dynamic, bidirectional alternative which leverages the CINT and Python reflection data.

Based on our experience, we (a collaboration between CERN and Fermilab, US) have decided to replace CINT with a new interpreter: cling (http://cern.ch/cling). It is built on top of clang (http://clang.llvm.org) and LLVM (http://llvm.org). This gives us just-in-time compilation, a high-quality front-end and compiler-grade reflection data. I will present how we built an interpreter out of compiler libraries.

Speaker Info: Axel is a physicist by education. After stopovers in Germany, The Netherlands (NIKHEF) and the US (Fermilab) he became scientist at CERN in 2005. As a member of the ROOT (http://root.cern.ch) team, Axel is responsible for interpreters and reflection. He is involved in many other areas like algorithms and data structures, bringing software to current architectures (multi-code, vectorization) and software quality assurance. He recently became CERN's representative to the ISO C++ Standards Committee.

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  Science & Technology

[rkulla]

from boson import higgs

[cantares1]

If someone want to follow the youtube link in the presentation.. that what looks like an "I" is the number one.. so it would be BrjV1ZgYbbA ..

[jehandadkhan]

Can we create breakpoints in code and have cling fire the function and debug it ?

[doug65536]

I wish google would put proper closed captions on these. Would it really be that hard? The speaker in this video is unintelligible.

[André Freitas]

How do we link a source file in cling?

[Vassil Vassilev]

Yes that is possible in principle. Have a look at cling::Transaction class.

[labobo]

Another clang compiler part that do not provide windows compatible binaries

You make binaries for mac but not windows ?! God damn it !

[ochgottnochma]

Is it possible for cling to use C++ like Lisp? Accessing the own interpreted program at runtime?

[zedboson]

This is really cool. Testing .cc source on the fly while editing would be really helpful for me.

[whotaughtyou]

ACCURIST CHRONOGRAPH WR 100M SCREEN GREEN THE COCK AND BULL

[laurent mallet]

Excellent. I try it but i can't reload a source. I try the .U (as unload) command but it seems not implemented.

[Mark Rebane]

Thank you, I tried the link and had the same problem :)