This is an interpreter for nock, Urbit's purely functional machine code, that I wrote in an afternoon.
This is by no means production ready, as it does not respect hints (opcode 11), but it does moderately non-trivial code, for example, the decrement function provided at the end of this page runs without error, thus all the opcodes function properly, just slowly (again, because of the lack of respecting hints).
Examples:
CL-USER> #n[42 [[0 1] [1 0]]]
(42 (0 . 1) 1 . 0)
CL-USER> (nock:tar #n[42 [[0 1] [1 0]]])
(42 . 0)
CL-USER> (nock:tar #n[3 [8 [1 0] 8 [1 6 [5 [0 7] 4 0 6] [0 6] 9 2 [0 2] [4 0 6] 0 7] 9 2 0 1]])
2The only exposed functions are a reader macro (#n), which will read
an [] expression, as demonstrated above, and tar, which will
interpret the machine code found. The combination of these two
functions allows for a well-integrated and easy development
experience.