Expose [first_symbol].

src/grammarFunctor.ml

@@ -1372,6 +1372,8 @@ module Analysis = struct
 
   let first = FIRST.nonterminal
 
+  let first_symbol = FIRST.symbol
+
   (* An initial definition of [nullable_first_prod]. *)
 
   let nullable_first_prod prod i =

src/grammarFunctor.mli

@@ -438,6 +438,7 @@ module Analysis : sig
   (* [first nt] is the FIRST set of the non-terminal symbol [nt]. *)
 
   val first: Nonterminal.t -> TerminalSet.t
+  val first_symbol: Symbol.t -> TerminalSet.t
 
   (* [nullable_first_prod prod i] considers the suffix of the production
      [prod] defined by offset [i]. It returns its NULLABLE flag as well