Make regular and parsing functions more parallel w.r.t. statements.
Make regular and parsing functions more parallel w.r.t. statements.

The upshot of this change is that if a parser function has `|`-separated
clauses, and any of those clauses wants to do result filtering, then
the whole clause has to be enclosed in "parser braces" `{: ... :}`.

danfuzz/samizdat,danfuzz/samizdat,danfuzz/samizdat,danfuzz/samizdat