Regex op specs can currently pass with maps or sets (which are unordered) but may give confusing errors.
Cause: Conforming fails because the first value of the map (the tuple pair `["foo" "bar"]`) is not a keyword
Proposed: Regex op specs currently check `coll?`, which will pass unordered collections like sets or maps - this is unlikely to be useful for positional regex specs. Propose to narrow that check to `sequential?`. On failure, use an explain pred that describes the actual check (the current one just repeats the regex spec instead).
With the patch, the message actually tells you the actual predicate that is failing (the sequential? check):
Screened by: Chouser - while making unordered colls invalid is the intent of the patch, a gray area is that of sorted colls (sorted sets, etc). These could have been matched with the prior impl, but will not be after the change. See comments for more examples.