Sequences, Lists, and Relational Constraint Expressions

[John Caron]

> 
> I like this idea. I think its important, where possible, that the data 
> structures "know" what are the valid queries allowed on them. Sequences 
> are doing 2 things: 1) indicating that an array of Structure has a 
> variable length (ie a List). This gives us "ragged arrays" when nested, 
> which is quite powerful. 2) indicating that relational queries are 
> allowed on the fields. Obviously very powerful, but difficult to 
> implement efficiently for all fields. 

Right now, you can do one without the other.
	       ^ can't