Function f 

pub fn f(
    name: impl Into<Cow<'static, str>>,
    args: impl IntoExprList,
) -> Function

A function call: f("count", "*"), f("row_number", ()).over(()).

Returns keelson-sqlite’s own Function, which carries DISTINCT, the aggregate ORDER BY, FILTER and OVER — everything SQLite hangs off a call and core deliberately does not know about.