Quantum Computing and Lisp

Quantum Computing is a fascinating field, but currently a contentious one. The only examples we have of real-world, hardware quantum computers are the line of adiabatic quantum computers from D-Wave Systems—and many voices in the scientific community still protest its identification as such simply because it is not a full-fledged gate-model quantum computer complete with persistent quantum data storage and QRAM. However, by the strictest definition, any machine which exploits quantum mechanical phenomena for the purpose of computation is a quantum computer, and the D-Wave One and Two meet this definition.

For us in the Lisp community, Quantum Computing is even more important; one of the most surprising secrets of the D-Wave line of adiabatic quantum computers is that their low-level operating system is programmed in Common Lisp. Specifically, D-Wave uses SBCL. This choice is not accidental or arbitrary—Common Lisp is uniquely suited to the task of quantum computer programming.

LET-OVER-LAMBDA fixed for SBCL 1.2.2

Thanks go out to Orivej Desh—he pointed out what I overlooked, and the LET-OVER-LAMBDA package now works with full functionality restored in SBCL 1.2.2. I have preserved the :safe-sbcl feature used for testing the version of SBCL, so that descending into comma-expr of sb-impl::comma is only enabled for SBCL 1.2.2+.

The updated code should be available in the August release of Quicklisp. If you have a fork or clone, please be certain to pull the latest changes from the master branch.

LET-OVER-LAMBDA broken in SBCL 1.2.2

As expected, the Quicklisp distribution of LET-OVER-LAMBDA is broken by the changes to the backquote reader macro in SBCL 1.2.2; although I expect this change breaks a good portion of Paul Graham’s macro code examples from On Lisp, as well.

A quick-fix suggested on Reddit is to use a “pseudo-flatten” for SBCL that also descends into sb-impl::comma-expr of sb-impl::comma. I will be testing this fix today, and hopefully pushing an updated version for the August release of Quicklisp.

Stay tuned.

UPDATE: modified LOL:FLATTEN to descend into comma-expr of sb-impl::comma objects, but no joy. I have currently disabled DEFMACRO! based code in LET-OVER-LAMBDA until I can find a better solution, and tested this against both v1.2.2 and v1.2.0-1 of SBCL (so if nothing else, it will at least build without errors).

If anyone knows of a better solution, feel free to leave a comment here or on the GitHub Issue thread.