I went to bed a couple of hours ago but every time I started to drift off a mosquito buzzed by. Led to this train of thought - how would you build a Universal Turing Machine with hypertext as the engine of state?
Seemed natural to use the Web in the role of the tape in Turing's setup with URLs corresponding to the position on the tape. The path part can be tape-like. Imagine an infinite path: http://example.org/location/location/location ... To move left it's href="../location", to the right href="location/location" (I think...bit tired here :). Whatever, problem is the train crashes to the left. I'm pretty sure a single-ended tape would still be universal because it'd be like folding the normal tape and interleaving the cells. But I reckon it'd be better to stick with the standard tape config but with little sub-rules for the mapping, something like:
start at http://example.org/H
to move right:
if the final char of the URL is a L, remove it
else append a "R"
- and vice versa.
The content of the page http://example.org/HLL might then look like:
<html>
...
Symbol = 0
<a href="http://example.org/HLLL">Left</a>, <a href="http://example.org/HL">Right</a>
...
</html>
or it might 404, corresponding to Turing's blank symbol.
Reading from tape is a GET, writing is a PUT.
I think this is in keeping with the spirit of REST, there is no context kept on the server, the messages are self-contained. The client would have to know the rules for generating the new URLs, plus the instructions. Maybe a neat way of doing the instructions might be to have a series of linked scripts each corresponding to an instruction, effectively a second agent stepping through them.
Now I've had a glass of milk and a chunk of chocolate I'm off back to bed, hope that mosquito's gone. I'll leave criticism, improvement and implementation to other insomniacs.
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