PostgreSQL URL slug usable for indices

uaccent.sql

/**
 * original unaccent function isn't usable for indices
 */
CREATE OR REPLACE FUNCTION uaccent(text) RETURNS text AS
$uaccent$
  SELECT unaccent('unaccent',$1::text);
$uaccent$ LANGUAGE sql IMMUTABLE;

url_slug.sql

CREATE OR REPLACE FUNCTION url_slug(text) RETURNS text AS
$url_slug$
  SELECT trim(both '-' from
    regexp_replace(
      unaccent('unaccent', lower($1::text)),
      '[^a-z0-9]+', '-', 'g'
    )
  );
$url_slug$ LANGUAGE sql IMMUTABLE;