Why make another web-based repl for arc when there is already palsecam's evsrv [1], nostrademons' ArcLite [2], thaddeus' wterm project [3] and pg's prompt.arc? (Are there others?)
These projects don't serve identical purposes. Try Arc is meant to be a tool for introducing people to Arc in a hands-on way. Sandboxed eval makes this safe and Chris Done's jquery-console makes it convenient (that is, once I've worked some of the kinks out). It is probably suboptimal for real development though (beyond as some sort of scratchpad) since it doesn't offer persistence: accidentally refresh the page and you lose your work.
prompt.arc, on the other hand, is nice for real development. Not only can you try things out at the repl, but you can plug them in as real applications at the prompt. However, it wouldn't be as good in the Try Arc context since it calls raw eval, granting access to the underlying system (it's a double-edged sword).
evsrv is great. Sandboxed eval plus persistence for multiple users, and you can even start an anonymous session, all at an ajaxified terminal? palsecam mentioned in [4] that he used mzscheme for sandboxing as well; there may be some useful ideas in what he's done for this project.
I haven't actually tried what thaddeus did, has anybody else? I also have less to say about ArcLite, except that it's awesome he got a working implementation of Arc in JavaScript.
