Alex Shinn scripsit:

> We should document whether or not it's an error to
> mutate a set while it is being folded over (I would say
> it's an error).

Added.  I have also added the analogue of `iset-update!` from
ImmutableDataStructuresWortman under the name of `set-search!`.
The name comes from HashTablesCowan, where `update!` is in use
for something else.

--
John Cowan <xxxxxx@ccil.org>             http://www.ccil.org/~cowan
Sir, I quite agree with you, but what are we two against so many?
    --George Bernard Shaw,
         to a man booing at the opening of _Arms and the Man_