Function fold_exprs

pub fn fold_exprs<F, E>(
    acc: Expr,
    f: F,
    exprs: E,
    returns_scalar: bool,
    return_dtype: Option<DataType>,
) -> Expr
where
    F: 'static + Fn(Column, Column) -> Result<Option<Column>, PolarsError> + Send + Sync,
    E: AsRef<[Expr]>,

Accumulate over multiple columns horizontally / row wise.