pub fn reparse_infix<'ast, Id>(
    arena: ArenaRef<'_, 'ast, Id>,
    metadata: &FnvMap<Id, Arc<Metadata>>,
    symbols: &dyn IdentEnv<Ident = Id>,
    expr: &mut SpannedExpr<'ast, Id>
) -> Result<(), ParseErrors>where
    Id: Clone + Eq + Hash + AsRef<str> + Debug,