start -> expr [SimNode]
  assign-expr -> or-expr assign-op assign-expr [SimNode]
    primary-expr -> IDENT [SimNode]
      IDENT
    assign-op -> ASSIGN [SimNode]
      ASSIGN
    shift-expr -> shift-expr shift-op add-expr [SimNode]
      primary-expr -> NUMBER [SimNode]
        NUMBER
      shift-op -> LSHIFT [SimNode]
        LSHIFT
      add-expr -> add-expr add-op mul-expr [SimNode]
        primary-expr -> NUMBER [SimNode]
          NUMBER
        add-op -> PLUS [SimNode]
          PLUS
        mul-expr -> mul-expr mul-op unary-expr [SimNode]
          primary-expr -> NUMBER [SimNode]
            NUMBER
          mul-op -> TIMES [SimNode]
            TIMES
          primary-expr -> NUMBER [SimNode]
            NUMBER