Chicken/egg problem with range types

[Scott Bailey <artacus72@xxxxxxxxx>]

I'm trying to create a discrete range type and I'm having trouble with 
the canonical function.

--Create shell type
CREATE TYPE dt_range;

--Create subtype diff
CREATE OR REPLACE FUNCTION dt_subtype_diff(timestamptz, timestamptz)
RETURNS float8 AS
$$
  SELECT EXTRACT(EPOCH FROM $1 - $2);
$$ LANGUAGE 'sql' IMMUTABLE STRICT;

-- Create the canonical function
CREATE OR REPLACE FUNCTION dt_range_canonical(dt_range)
RETURNS dt_range AS
$$
  SELECT dt_range(
    CASE WHEN lower_inc($1)
        THEN lower($1)::timestampTz(0)
        ELSE lower($1)::timestampTz(0) - INTERVAL '1s' END,
    CASE WHEN NOT upper_inc($1)
        THEN upper($1)::timestampTz(0)
        ELSE upper($1)::timestampTz(0) + INTERVAL '1s' END
  );
$$ LANGUAGE 'sql' IMMUTABLE STRICT;

Fails with ERROR: SQL function cannot accept shell type dt_range. So I 
add the type and try to alter it later.

-- Create the type any way
CREATE TYPE dt_range AS RANGE (
  SUBTYPE = timestamptz,
  SUBTYPE_DIFF = dt_subtype_diff
  -- CANONICAL = dt_range_canonical -- can't use, fn doesn't exist
);

ALTER TYPE dt_range SET CANONICAL = dt_range_canonical;

This doesn't work either. I'm stuck.

Scott Bailey

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