I asked GPT-4 to take a whack at it:

ChatGPT:

I see that you've posted a TECO program, a Universal Turing Machine emulator, from Marvin Minsky's directory, shared via Hacker News.

TECO (Text Editor and COrrector) is a text editor that was very popular and widely used in the 1960s and 1970s, especially on DEC computers. It's an extremely powerful and flexible editor, but also notoriously difficult to understand and use. In fact, it's often used as an example of a "write-only" language, because its programs can be extremely hard to read and understand, even for people who are familiar with TECO.

This TECO program is indeed cryptic. Its syntax involves lots of non-alphanumeric symbols and control characters, which are typical of TECO. Reading and understanding this code would require a deep understanding of TECO's syntax and commands.

TECO code is composed of commands that are read and executed one after the other. Each command can have an optional numeric argument, and can also have another command as an argument. This allows for complex, powerful operations, but also makes the code difficult to read.

If you're interested in understanding how this TECO program works, I'd recommend starting by learning more about TECO's syntax and commands. Be aware, though, that this is not a trivial task; even experienced programmers often find TECO challenging to understand.

As the Hacker News comments note, this program is written in ITS TECO, a version of TECO used on the Incompatible Timesharing System (ITS) developed at MIT. This version of TECO has some differences from other versions, so you would need to find documentation specifically for ITS TECO in order to fully understand the program.

User:

How much of it can you understand? Explain what you can.

ChatGPT:

I must point out that while I'm able to provide explanations on many topics, TECO is one of the most cryptic and complex programming languages ever created. TECO programs are notoriously difficult to read, and even people who are experienced with TECO often struggle to understand non-trivial programs written in it. Therefore, please take the following explanation with a grain of salt as it may be simplified or not entirely accurate due to the complexity of TECO.

Here's a breakdown of a few commands, as far as I can understand:

i1Aul qq+^^0:iqm^[29iiq\356y0L1 00L1 11L2 A1L1: This line initializes several variables. The i command inserts text, A assigns the value of the last text string searched for to a variable (qq in this case), ul is probably used to move the cursor to the left. There are other commands to move around the buffer and do arithmetic operations. The line ends with assigning a string to variable qy and the insertion of several pairs of numbers and letters.

y0L1 0yR2 1AR2 AyR6 yyL3 00L0 1AL3 A1L4 yyL4 0yR5 11L7 A1L4...: This line continues with similar commands, modifying the state of the buffer and several variables.

^[j<sR^[;-d-2ciql-^^^[ci"ed^^^[cii^[ciuq'^[>: This part seems to be a conditional jump loop, a fundamental structure in TECO. The j command moves to the beginning of the buffer. The < and > delimit a loop, and s searches for a string. The ; command conditionally terminates the loop.

jxblx1lx2lx3lx4lx5lx6lx7hk: This line seems to be doing various operations on buffers, possibly saving or loading state. x executes a macro, l loads a file into a buffer, h moves to the top of the current buffer, and k kills the current buffer.

iyyAyyAyy^[32<i0^[>ji110101110000010011011^[ 1uq<htmbqq=>: This line again modifies buffers and variables and includes another loop structure. The long string of numbers seems to be data for the Turing machine, and the uq command updates a Q-register.

Please note that this is a high-level interpretation and might contain inaccuracies. Fully understanding this program would require a deep understanding of TECO and possibly access to its original documentation. As such, this program is a great example of the complexity and cryptic nature of TECO.