Add $_as_string convenience function

diff --git a/gdb/data-directory/Makefile.in b/gdb/data-directory/Makefile.in
index f6d959f..c05f379 100644
--- a/gdb/data-directory/Makefile.in
+++ b/gdb/data-directory/Makefile.in
@@ -74,6 +74,7 @@  PYTHON_FILE_LIST = \
 	gdb/command/prompt.py \
 	gdb/command/explore.py \
 	gdb/function/__init__.py \
+	gdb/function/as_string.py \
 	gdb/function/caller_is.py \
 	gdb/function/strfns.py \
 	gdb/printer/__init__.py \
diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index 4ec0ec1..0b249f4 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -10760,6 +10760,19 @@  checks all stack frames from the immediate caller to the frame specified
 by @var{number_of_frames}, whereas @code{$_caller_matches} only checks the
 frame specified by @var{number_of_frames}.
 
+@item $_as_string(@var{value})
+@findex $_as_string@r{, convenience function}
+Return the string representation of @var{value}.
+
+This function is useful to obtain the textual label (enumerator) of an
+enumeration value.  For example, assuming the variable @var{node} is of
+an enumerated type:
+
+@smallexample
+(gdb) printf "Visiting node of type %s\n", $_as_string(node)
+Visiting node of type NODE_INTEGER
+@end smallexample
+
 @end table
 
 @value{GDBN} provides the ability to list and get help on
diff --git a/gdb/python/lib/gdb/function/as_string.py b/gdb/python/lib/gdb/function/as_string.py
new file mode 100644
index 0000000..d55a466
--- /dev/null
+++ b/gdb/python/lib/gdb/function/as_string.py
@@ -0,0 +1,39 @@ 
+# Copyright (C) 2016 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+import gdb
+
+
+class _AsString(gdb.Function):
+    """Return the string representation of a value.
+
+Usage:
+  $_as_string(value)
+
+Arguments:
+
+  value: A gdb.Value.
+
+Returns:
+  The string representation of the value.
+"""
+
+    def __init__(self):
+        super(_AsString, self).__init__("_as_string")
+
+    def invoke(self, val):
+        return str(val)
+
+_AsString()
diff --git a/gdb/testsuite/gdb.python/py-as-string.c b/gdb/testsuite/gdb.python/py-as-string.c
new file mode 100644
index 0000000..efdf988
--- /dev/null
+++ b/gdb/testsuite/gdb.python/py-as-string.c
@@ -0,0 +1,32 @@ 
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2016 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+enum EnumType {
+  ENUM_VALUE_A,
+  ENUM_VALUE_B,
+  ENUM_VALUE_C,
+  ENUM_VALUE_D,
+};
+
+static enum EnumType enum_valid = ENUM_VALUE_B;
+static enum EnumType enum_invalid = 20;
+
+int
+main ()
+{
+  return 0;
+}
diff --git a/gdb/testsuite/gdb.python/py-as-string.exp b/gdb/testsuite/gdb.python/py-as-string.exp
new file mode 100644
index 0000000..4c7dd0d
--- /dev/null
+++ b/gdb/testsuite/gdb.python/py-as-string.exp
@@ -0,0 +1,40 @@ 
+# Copyright (C) 2016 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+# This file is part of the GDB testsuite.  It tests the convenience
+# functions in as_string.py.
+
+load_lib gdb-python.exp
+
+standard_testfile
+
+if { [prepare_for_testing ${testfile}.exp ${testfile} ${srcfile}] } {
+    return -1
+}
+
+if ![runto_main] {
+    fail "Couldn't run to main."
+    return 0
+}
+
+if { [skip_python_tests] } { continue }
+
+proc test_as_string { } {
+    gdb_test "p \$_as_string(2)" "\"2\""
+    gdb_test "p \$_as_string(enum_valid)" "\"ENUM_VALUE_B\""
+    gdb_test "p \$_as_string(enum_invalid)" "\"20\""
+}
+
+test_as_string