@type operator() ::
  :=
  | :"+="
  | :"-="
  | :"*="
  | :"/="
  | :"%="
  | :"<<="
  | :">>="
  | :"&="
  | :"|="
  | :"^="

@type t() :: %JustBash.AST.ArithAssignment{
  operator: operator(),
  string_key: String.t() | nil,
  subscript: JustBash.AST.arith_expr() | nil,
  value: JustBash.AST.arith_expr(),
  variable: String.t()
}