CREATE parametric partial INDEX within a function body

Hi all.

I have a maintenance PL/pgSQL function that needs to recreate a partial index
(not a REINDEX, though).
In the WHERE condition of the index I have one of the function arguments.
A plain "CREATE INDEX ... WHERE ..." will lead to a runtime error like this:

tmp2=# SELECT * FROM f_maint1( '20080401'::timestamptz );
ERROR:  there is no parameter $1
CONTEXT:  SQL statement "CREATE INDEX i_special_part ON t_atable( col1,col2 )
WHERE col3 >= $1 "
PL/pgSQL function "f_maint1" line 28 at SQL statement

To work this issue around I switched to dynamic SQL with "EXECUTE 'CREATE
INDEX ...' "
This means to me that the CREATE INDEX within a PL/pgSQL body cannot use
function arguments in the WHERE condition.

Is this the expected behavior?
If so, why?

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