* src/struniq.h, src/struniq.c (struniq_t): Is const.

(STRUNIQ_EQ, struniq_assert, struniq_assert_p): New.
Use struniq for symbols.
* src/symtab.h (symbol_t): The tag member is a struniq.
(symbol_type_set): Adjust.
* src/symtab.c (symbol_new): Takes a struniq.
(symbol_free): Don't free the tag member.
(hash_compare_symbol_t, hash_symbol_t): Rename as...
(hash_compare_symbol, hash_symbol): these.
Use the fact that tags as struniqs.
(symbol_get): Use struniq_new.
* src/symlist.h, src/symlist.c (symbol_list_n_type_name_get):
Returns a strniq.
* src/reader.h (merger_list, grammar_currentmerge_set): The name
and type members are struniqs.
* src/reader.c (get_merge_function)
(grammar_current_rule_merge_set): Adjust.
(TYPE, current_type): Are struniq.
Use struniq for file names.
* src/files.h, src/files.c (infile): Split into...
(grammar_file, current_file): these.
* src/scan-gram.c (YY_USER_INIT, handle_syncline): Adjust.
* src/reduce.c (reduce_print): Likewise.
* src/getargs.c (getargs): Likewise.
* src/complain.h, src/complain.c: Likewise.
* src/main.c (main): Call struniqs_new early enough to use it for
file names.
Don't free the input file name.

src/struniq.h

@@ -25,11 +25,14 @@
 | struniq_t -- pointers to unique copies of C strings.  |
 `------------------------------------------------------*/
 
-typedef char *struniq_t;
+typedef const char *struniq_t;
 
 /* Return the struniq for S.  */
 const struniq_t struniq_new (const char *s);
 
+/* Two struniq have the same value iff they are the same.  */
+#define STRUNIQ_EQ(S1, S2) ((S1) == (S2))
+
 /*--------------------------------------.
 | Initializing, destroying, debugging.  |
 `--------------------------------------*/
@@ -37,6 +40,10 @@ const struniq_t struniq_new (const char *s);
 /* Create the string table.  */
 void struniqs_new (void);
 
+/* Die if S is not a struniq.  */
+#define struniq_assert(S) assert (struniq_assert_p (S));
+bool struniq_assert_p (const char *s);
+
 /* Free all the memory allocated for symbols.  */
 void struniqs_free (void);