Problem about postgresql-simple

Hi, Anyone used this library? Just trying to use it and got problem. alias here is a String. kerb.hs:18:9: No instance for (Database.PostgreSQL.Simple.Param.Param Char) arising from a use of `query' Possible fix: add an instance declaration for (Database.PostgreSQL.Simple.Param.Param Char) In a stmt of a 'do' block: rs <- query conn "select 0 from users where alias = ?" (alias) -- 竹密岂妨流水过 山高哪阻野云飞