Allow setting of user pointer in grammar

Required for vnmakarov#12.

src/yaep.c

@@ -185,6 +185,8 @@ struct grammar
   struct term_sets *term_sets_ptr;
   /* Allocator. */
   YaepAllocator *alloc;
+  /* User pointer */
+  void *userptr;
 };
 
 /* The following variable value is the reference for the current
@@ -3049,9 +3051,40 @@ yaep_create_grammar (void)
   grammar->symbs_ptr = symbs_ptr = symb_init ();
   grammar->term_sets_ptr = term_sets_ptr = term_set_init ();
   grammar->rules_ptr = rules_ptr = rule_init ();
+  grammar->userptr = NULL;
   return grammar;
 }
 
+/* The following function sets the user pointer for a grammar. */
+#ifdef __cplusplus
+static
+#endif
+void
+yaep_grammar_setuserptr (struct grammar *g, void *userptr)
+{
+  if (g != NULL)
+    {
+      g->userptr = userptr;
+    }
+}
+
+/* The following function retrieves the user pointer of a grammar. */
+#ifdef __cplusplus
+static
+#endif
+void *
+yaep_grammar_getuserptr (struct grammar *g)
+{
+  if (g == NULL)
+    {
+      return NULL;
+    }
+  else
+    {
+      return g->userptr;
+    }
+}
+
 /* The following function makes grammar empty. */
 static void
 yaep_empty_grammar (void)

src/yaep.cpp

@@ -135,6 +135,18 @@ yaep::set_recovery_match (int n_toks)
   return yaep_set_recovery_match (this->grammar, n_toks);
 }
 
+void
+yaep::setuserptr (void *userptr) noexcept
+{
+  yaep_grammar_setuserptr (this->grammar, userptr);
+}
+
+void *
+yaep::getuserptr () const noexcept
+{
+  return yaep_grammar_getuserptr (this->grammar);
+}
+
 int
 yaep::parse (int (*read_token) (void **attr),
 	     void (*syntax_error) (int err_tok_num,

src/yaep.h

@@ -155,6 +155,16 @@ struct yaep_tree_node
    the first. */
 extern struct grammar *yaep_create_grammar (void);
 
+/* The following function stores a user-defined pointer
+   in the given grammar. */
+extern void yaep_grammar_setuserptr (struct grammar *g, void *userptr);
+
+/* The following function retrieves a user-defined pointer
+   previously set with yaep_grammar_setuserptr() from
+   the given grammar.  If no user pointer has been set,
+   a null pointer is returned. */
+extern void *yaep_grammar_getuserptr (struct grammar *g);
+
 /* The function returns the last occurred error code for given
    grammar. */
 extern int yaep_error_code (struct grammar *g);
@@ -353,6 +363,8 @@ class yaep
   int set_cost_flag (int flag);
   int set_error_recovery_flag (int flag);
   int set_recovery_match (int n_toks);
+  void setuserptr (void *userptr) noexcept;
+  void *getuserptr () const noexcept;
 
   /* See comments for function yaep_parse. */
   int parse (int (*read_token) (void **attr),