non-btree primary key

Hello,

looks like PostgreSQL (8.0/8.1) has no support for using
other-than-btree indexes for primary keys. Is there a (perhaps
un(der)documented) way to specify the index type?

Rationale: I'm trying to have PKs on a type that defines only the = and
<> operators, and would work with a hash-based PK. I know I could work
around it with a UNIQUE INDEX, but would like to avoid that for exactly
the reason described in the manual:

: Technically, PRIMARY KEY is merely a combination of UNIQUE and NOT
: NULL, but identifying a set of columns as primary key also provides
: metadata about the design of the schema, as a primary key implies
: that other tables may rely on this set of columns as a unique
: identifier for rows.

Please cc me on replies, I have problems with the postgresql.org
majordomo.

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