[Ur] type system expressivity

[Adam Chlipala]

Gergely Buday wrote:
> I have a data structure that is a list of records, and in the records
> there might be lists as fields.
>
> Is it possible to write a generic map function in ur/web that applies
> a function for every basic value in this structure, i.e. those that
> are not records and not lists?
>    

Could you provide a bit more context?  A single function can't be 
expected to do much useful work on values of arbitrary "basic" types.