CREATE OR REPLACE LANGUAGE plperl;

CREATE OR REPLACE FUNCTION test1(x int) RETURNS int
IMMUTABLE STRICT
LANGUAGE plperl
AS $$
elog(ERROR, "boom") if $_[0] < 0;
return $x;
$$;

DROP TABLE IF EXISTS test;
CREATE TABLE test (a int, b text);

CREATE INDEX ON test ((test1(a)));

CREATE OR REPLACE FUNCTION test2(a int, b text) RETURNS int
LANGUAGE plperl
AS $$
$plan = spi_prepare('INSERT INTO test (a, b) VALUES ($1, $2)', 'int', 'text');
$rv = spi_exec_prepared($plan, $_[0], $_[1]);
return $rv->{processed};
$$;

SELECT test2(1, 'one');
SELECT test2(-1, 'neg one');

SELECT * FROM test;