The Original

Robert Smith, a.k.a. stylewarning, has a lovely blog post that walks through implementing an interpreter for a “general-purpose quantum programming language called \( \mathscr{L} \).” In only 150 lines of Common Lisp, the implementation is featureful, self-contained, and a delight to read.

Imitation is the highest form of flattery

At first I was content with only reading the post and code, but then I saw someone else had put together an OCaml implementation as well. The game was afoot!

Carcinization

Eventually I put together a Rust implementation. This version weights in at more than twice the line count as the original—even though it relies on faer for linear algebra instead of implementing it by hand!¹ However, it does have a couple of features not present in the original (or OCaml) implementation(s):

• constructing a Machine takes an unsigned 64-bit seed for repeatable PRNG behavior; and
• with the help of the peg crate, I added parsing, so one can pass "H 0\nMEASURE" as a string and get an interpretable quantum program.

Code or it didn’t happen

The implementation is here in my catch-all “workbench” repository. It’s definitely not production-worthy code; it’s got an assert! that will panic if not met, and it uses expect to pave over some errors.² Please feel free to take a look and let me know what you think!