David Barbour <[email protected]> writes:
> Text is also one of the problems I've been banging my head against since
> Friday. Thing is, I really hate escapes. They have this nasty geometric
> progression when dealing with deeply quoted code:
>
> {} -> {{\}} -> {{{\\\}\}} -> {{{{\\\\\\\}\\\}\}} ->
> {{{{{\\\\\\\\\\\\\\\}\\\\\\\}\\\}\}}
>
> I feel escapes are too easy to handle incorrectly, and too difficult to
> inspect for correctness. I'm currently contemplating a potential solution:
> require all literal text to use balanced `{` and `}` characters, and use
> post-processing in ABC to introduce any imbalance. This could be performed
> in a streaming manner. Inductively, all quoted code would be balanced.
The geometric explosion comes from the unary nature of escaping. It
wouldn't be too difficult to add a 'level', for example:
{} -> {{\0}} -> {{{\1}\0}} -> {{{{\2}\1}\0}} ->
{{{{{\3}\2}\1}\0}}
The main problem with escaping is that it is homomorphic: ie. it is
usually "String -> String". This is basically the source of all code
injection attacks. It wouldn't be too bad if escaping were idempotent,
since we could add extra escapes just in case, but it's not so we end up
keeping track manually, and failing.
There's a good post on this at
http://blog.moertel.com/posts/2006-10-18-a-type-based-solution-to-the-strings-problem.html
It would be tricky to implement a solution to this in a way that's open
and extensible; if we're be passing around first-class functions anyway,
we could do Haskell's dictionary-passing manually.
Cheers,
Chris
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