+
+
+## ---------------------------------------------------------------------- ##
+## Duplicate representation of merged trees ##
+## Thanks to Joel E. Denny for this test; see ##
+## <http://lists.gnu.org/archive/html/help-bison/2005-07/msg00013.html>. ##
+## ---------------------------------------------------------------------- ##
+
+AT_SETUP([Duplicate representation of merged trees])
+
+AT_DATA_GRAMMAR([glr-regr4.y],
+[[%union { char *ptr; }
+%type <ptr> S A A1 A2 B
+%glr-parser
+
+%{
+ #include <stdio.h>
+ #include <stdlib.h>
+ #include <string.h>
+ static char *merge (YYSTYPE, YYSTYPE);
+ static char *make_value (char *, char *);
+ static void yyerror (char const *);
+ static int yylex (void);
+%}
+
+%%
+
+tree: S { printf ("%s\n", $1); } ;
+
+S:
+ A %merge<merge> { $$ = make_value ("S", $1); }
+ | B %merge<merge> { $$ = make_value ("S", $1); }
+ ;
+
+A:
+ A1 %merge<merge> { $$ = make_value ("A", $1); }
+ | A2 %merge<merge> { $$ = make_value ("A", $1); }
+ ;
+
+A1: 'a' { $$ = make_value ("A1", "'a'"); } ;
+A2: 'a' { $$ = make_value ("A2", "'a'"); } ;
+B: 'a' { $$ = make_value ("B", "'a'"); } ;
+
+%%
+
+static int
+yylex (void)
+{
+ static char const *input = "a";
+ return *input++;
+}
+
+int
+main (void)
+{
+ return yyparse ();
+}
+
+static char *
+make_value (char *parent, char *child)
+{
+ char const format[] = "%s <- %s";
+ char *value = malloc (strlen (parent) + strlen (child) + sizeof format);
+ sprintf (value, format, parent, child);
+ return value;
+}
+
+static char *
+merge (YYSTYPE s1, YYSTYPE s2)
+{
+ char const format[] = "merge{ %s and %s }";
+ char *value = malloc (strlen (s1.ptr) + strlen (s2.ptr) + sizeof format);
+ sprintf (value, format, s1.ptr, s2.ptr);
+ return value;
+}
+
+static void
+yyerror (char const *msg)
+{
+ printf ("%s\n", msg);
+}
+]])
+
+AT_CHECK([[bison -o glr-regr4.c glr-regr4.y]], 0, [],
+[glr-regr4.y: conflicts: 1 reduce/reduce
+])
+AT_COMPILE([glr-regr4])
+
+AT_CHECK([[./glr-regr4]], 0,
+[[merge{ S <- merge{ A <- A1 <- 'a' and A <- A2 <- 'a' } and S <- B <- 'a' }
+]], [])
+
+AT_CLEANUP