Board with an embedded scheme interpreter

I've spent long nights meditating on this and I think I have a design that could work.

Commands are normal scheme expressions embedded in text, for example a post body of "Hello, number (+ 2 3)" would output "Hello, number 5". Literal parenthesis would need to be escaped with a backslash. All expressions are evaluated and their output displayed except for define expressions, which are both evaluated and displayed.

Each thread is roughly equivalent to a scheme session. Names defined in parent posts are available to subsequent posts in the thread. Names are immutable within a thread; symbols cannot be redefined.

Obviously a set of primitives should be provided: the basic arithmetic operations; a display operation; a set of formatting operations roughly equivalent in capability to today's BBCode; and, of course, our old friends cons, car and cudder.

What say you, /prog/? Can we do this thing?

What about the security issues this could raise?

What security issues? This would be just like BBCode but more Touring Complete.

>>2
The security issues wouldn't matter, since it would only be /prog/riders using the site and we would be to busy implementing web 1.0 monstrosities like <blink> in [b]^B_bcode[/spoiler] to exploit it

>>2
No file IO and an execution time limit

what happens if the user writes code that will cause a stack overflow?

BBcode Failure ;_;

>>1
That would be cool, though how would you store symbols like functions?

>>8
In the first iteration, just eval the whole thread each time it's rendered, keeping a table of name => expression mappings for functions and variables defined with define.

>>1
That the entire thread is a session is an interesting twist, though I'm not sure I agree with immutable names. If >>1 references post 1, what would (>>1) mean to you? I'm thinking something along the lines of PLT Scheme's modules, looking at (>>1) like (require "1.post"). In theory this could also reference other threads.

This could be cool if we integrated it with Google Wave

>>10
Mutable names would let the posters above you redefine + and maybe display. I guess that could be fun though.

I think (>>1) should display the content of post 1, though I'm not at all sure. Should ("hello") output hello or should it be an error? It'd be nice to do (b >>1), (rot13 >>1), (gpl >>1) and (faggot-quote >>1). Including other threads would be interesting. Some sort of library inclusion mechanism is needed I think.

>>12

I figured (>>1) would take all the defines from >>1 and bring them into the scope of the current post.

Please sell it to us with a couple of conceptual example sessions that show off the potential awesomeness.

>>11
if
Sir, you seem to lack understanding about how flexible Wave is.

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