Ocaml 美元+；mly中的标识符

我在类型检查器的

.mly

中看到

$startpos

和

$endpos

：

recursive_def:
| f = term_variable
  ty_args = multiple(formal_type_arguments)
  te_args = multiple(term_arguments)
  codomain = preceded(COLON,typ)
  EQ t = loc(term)
    { let loc = ($startpos(ty_args), $endpos(t)) in
      make_recursive_definition f loc ty_args te_args codomain t }
    (* one should check that the right-hand side of a recursive definition
       is a value, e.g. a function or a data constructor application; this
       is not done for the moment. *)

...

pattern:
| d = data_constructor tvars = multiple(formal_type_arguments) LBRACE fields = semi(term_variable) RBRACE
    { SynPatData (($startpos, $endpos), d, tvars, fields) }

...

(* Recording locations. *)

loc(TERM):
| t = TERM
    { SynTeLoc (($startpos, $endpos), t) }

---

谁能告诉我

$

+

标识符的含义是什么？它们是函数还是变量？它们的值是如何输入的？
这些是由定义的内部符号

这些是由定义的内部符号

$startpos  start position of the first symbol in the
           production’s right-hand side, if there is one;
           end position of the most recently parsed symbol, otherwise

$endpos    end position of the first symbol in the production’s
           right-hand side, if there is one; end position of the
           most recently parsed symbol, otherwise

$startpos($i | id)  start position of the symbol named $i or id

$endpos($i | id)    end position of the symbol named $i or id