You had me worried, but I'm pretty sure there's absolutely no problem with using strings as the keys for tables.
The MzScheme documentation says: make-hash-table ... 'equal -- creates a hash table that compares keys using equal? instead of eq? (needed, for example, when using strings as keys).
Checking ac.scm, sure enough:
(xdef 'table (lambda () (make-hash-table 'equal))
Likewise, the "is" operation in Arc uses MzScheme's string=? . (That's a statement, not a question :-) So string comparison works, although in O(n) time.
Net net: strings are okay for comparison and table keys in Arc.
I wasn't saying that they weren't usable, just that they were, in fact, slower; that's what you observed. Symbol comparison is O(1) time, whereas string comparison is O(n) time. That's all.
