diff --git a/Include/asdl.h b/Include/asdl.h
index 549df2a..e962560 100644
--- a/Include/asdl.h
+++ b/Include/asdl.h
@@ -4,9 +4,7 @@
 
 typedef PyObject * identifier;
 typedef PyObject * string;
-typedef PyObject * bytes;
 typedef PyObject * object;
-typedef PyObject * singleton;
 typedef PyObject * constant;
 
 /* It would be nice if the code generated by asdl_c.py was completely
diff --git a/Lib/test/test_ast.py b/Lib/test/test_ast.py
index a8a13fd..6b71ada 100644
--- a/Lib/test/test_ast.py
+++ b/Lib/test/test_ast.py
@@ -597,7 +597,7 @@
         empty_yield_from.body[0].body[0].value.value = None
         with self.assertRaises(ValueError) as cm:
             compile(empty_yield_from, "<test>", "exec")
-        self.assertIn("field value is required", str(cm.exception))
+        self.assertIn("field 'value' is required", str(cm.exception))
 
     @support.cpython_only
     def test_issue31592(self):
diff --git a/Parser/Python.asdl b/Parser/Python.asdl
index f789f1d..889712b 100644
--- a/Parser/Python.asdl
+++ b/Parser/Python.asdl
@@ -1,5 +1,5 @@
--- ASDL's 5 builtin types are:
--- identifier, int, string, object, constant
+-- ASDL's 4 builtin types are:
+-- identifier, int, string, constant
 
 module Python
 {
diff --git a/Parser/asdl.py b/Parser/asdl.py
index 5416377..7f50948 100644
--- a/Parser/asdl.py
+++ b/Parser/asdl.py
@@ -33,8 +33,7 @@
 # See the EBNF at the top of the file to understand the logical connection
 # between the various node types.
 
-builtin_types = {'identifier', 'string', 'bytes', 'int', 'object', 'singleton',
-                 'constant'}
+builtin_types = {'identifier', 'string', 'int', 'constant'}
 
 class AST:
     def __repr__(self):
diff --git a/Parser/asdl_c.py b/Parser/asdl_c.py
index c98f949..59bf03e 100755
--- a/Parser/asdl_c.py
+++ b/Parser/asdl_c.py
@@ -323,7 +323,7 @@
             if not opt and argtype != "int":
                 emit("if (!%s) {" % argname, 1)
                 emit("PyErr_SetString(PyExc_ValueError,", 2)
-                msg = "field %s is required for %s" % (argname, name)
+                msg = "field '%s' is required for %s" % (argname, name)
                 emit('                "%s");' % msg,
                      2, reflow=False)
                 emit('return NULL;', 2)
@@ -853,11 +853,9 @@
     Py_INCREF((PyObject*)o);
     return (PyObject*)o;
 }
-#define ast2obj_singleton ast2obj_object
 #define ast2obj_constant ast2obj_object
 #define ast2obj_identifier ast2obj_object
 #define ast2obj_string ast2obj_object
-#define ast2obj_bytes ast2obj_object
 
 static PyObject* ast2obj_int(long b)
 {
@@ -1147,12 +1145,8 @@
             self.emit("case %s:" % t.name, 2)
             self.emit("Py_INCREF(astmodulestate_global->%s_singleton);" % t.name, 3)
             self.emit("return astmodulestate_global->%s_singleton;" % t.name, 3)
-        self.emit("default:", 2)
-        self.emit('/* should never happen, but just in case ... */', 3)
-        code = "PyErr_Format(PyExc_SystemError, \"unknown %s found\");" % name
-        self.emit(code, 3, reflow=False)
-        self.emit("return NULL;", 3)
         self.emit("}", 1)
+        self.emit("Py_UNREACHABLE();", 1);
         self.emit("}", 0)
 
     def visitProduct(self, prod, name):
diff --git a/Python/Python-ast.c b/Python/Python-ast.c
index 80f9164..f34b145 100644
--- a/Python/Python-ast.c
+++ b/Python/Python-ast.c
@@ -1294,11 +1294,9 @@
     Py_INCREF((PyObject*)o);
     return (PyObject*)o;
 }
-#define ast2obj_singleton ast2obj_object
 #define ast2obj_constant ast2obj_object
 #define ast2obj_identifier ast2obj_object
 #define ast2obj_string ast2obj_object
-#define ast2obj_bytes ast2obj_object
 
 static PyObject* ast2obj_int(long b)
 {
@@ -2077,7 +2075,7 @@
     mod_ty p;
     if (!body) {
         PyErr_SetString(PyExc_ValueError,
-                        "field body is required for Expression");
+                        "field 'body' is required for Expression");
         return NULL;
     }
     p = (mod_ty)PyArena_Malloc(arena, sizeof(*p));
@@ -2094,7 +2092,7 @@
     mod_ty p;
     if (!returns) {
         PyErr_SetString(PyExc_ValueError,
-                        "field returns is required for FunctionType");
+                        "field 'returns' is required for FunctionType");
         return NULL;
     }
     p = (mod_ty)PyArena_Malloc(arena, sizeof(*p));
@@ -2114,12 +2112,12 @@
     stmt_ty p;
     if (!name) {
         PyErr_SetString(PyExc_ValueError,
-                        "field name is required for FunctionDef");
+                        "field 'name' is required for FunctionDef");
         return NULL;
     }
     if (!args) {
         PyErr_SetString(PyExc_ValueError,
-                        "field args is required for FunctionDef");
+                        "field 'args' is required for FunctionDef");
         return NULL;
     }
     p = (stmt_ty)PyArena_Malloc(arena, sizeof(*p));
@@ -2148,12 +2146,12 @@
     stmt_ty p;
     if (!name) {
         PyErr_SetString(PyExc_ValueError,
-                        "field name is required for AsyncFunctionDef");
+                        "field 'name' is required for AsyncFunctionDef");
         return NULL;
     }
     if (!args) {
         PyErr_SetString(PyExc_ValueError,
-                        "field args is required for AsyncFunctionDef");
+                        "field 'args' is required for AsyncFunctionDef");
         return NULL;
     }
     p = (stmt_ty)PyArena_Malloc(arena, sizeof(*p));
@@ -2181,7 +2179,7 @@
     stmt_ty p;
     if (!name) {
         PyErr_SetString(PyExc_ValueError,
-                        "field name is required for ClassDef");
+                        "field 'name' is required for ClassDef");
         return NULL;
     }
     p = (stmt_ty)PyArena_Malloc(arena, sizeof(*p));
@@ -2241,7 +2239,7 @@
     stmt_ty p;
     if (!value) {
         PyErr_SetString(PyExc_ValueError,
-                        "field value is required for Assign");
+                        "field 'value' is required for Assign");
         return NULL;
     }
     p = (stmt_ty)PyArena_Malloc(arena, sizeof(*p));
@@ -2265,17 +2263,17 @@
     stmt_ty p;
     if (!target) {
         PyErr_SetString(PyExc_ValueError,
-                        "field target is required for AugAssign");
+                        "field 'target' is required for AugAssign");
         return NULL;
     }
     if (!op) {
         PyErr_SetString(PyExc_ValueError,
-                        "field op is required for AugAssign");
+                        "field 'op' is required for AugAssign");
         return NULL;
     }
     if (!value) {
         PyErr_SetString(PyExc_ValueError,
-                        "field value is required for AugAssign");
+                        "field 'value' is required for AugAssign");
         return NULL;
     }
     p = (stmt_ty)PyArena_Malloc(arena, sizeof(*p));
@@ -2300,12 +2298,12 @@
     stmt_ty p;
     if (!target) {
         PyErr_SetString(PyExc_ValueError,
-                        "field target is required for AnnAssign");
+                        "field 'target' is required for AnnAssign");
         return NULL;
     }
     if (!annotation) {
         PyErr_SetString(PyExc_ValueError,
-                        "field annotation is required for AnnAssign");
+                        "field 'annotation' is required for AnnAssign");
         return NULL;
     }
     p = (stmt_ty)PyArena_Malloc(arena, sizeof(*p));
@@ -2331,12 +2329,12 @@
     stmt_ty p;
     if (!target) {
         PyErr_SetString(PyExc_ValueError,
-                        "field target is required for For");
+                        "field 'target' is required for For");
         return NULL;
     }
     if (!iter) {
         PyErr_SetString(PyExc_ValueError,
-                        "field iter is required for For");
+                        "field 'iter' is required for For");
         return NULL;
     }
     p = (stmt_ty)PyArena_Malloc(arena, sizeof(*p));
@@ -2363,12 +2361,12 @@
     stmt_ty p;
     if (!target) {
         PyErr_SetString(PyExc_ValueError,
-                        "field target is required for AsyncFor");
+                        "field 'target' is required for AsyncFor");
         return NULL;
     }
     if (!iter) {
         PyErr_SetString(PyExc_ValueError,
-                        "field iter is required for AsyncFor");
+                        "field 'iter' is required for AsyncFor");
         return NULL;
     }
     p = (stmt_ty)PyArena_Malloc(arena, sizeof(*p));
@@ -2394,7 +2392,7 @@
     stmt_ty p;
     if (!test) {
         PyErr_SetString(PyExc_ValueError,
-                        "field test is required for While");
+                        "field 'test' is required for While");
         return NULL;
     }
     p = (stmt_ty)PyArena_Malloc(arena, sizeof(*p));
@@ -2418,7 +2416,7 @@
     stmt_ty p;
     if (!test) {
         PyErr_SetString(PyExc_ValueError,
-                        "field test is required for If");
+                        "field 'test' is required for If");
         return NULL;
     }
     p = (stmt_ty)PyArena_Malloc(arena, sizeof(*p));
@@ -2519,7 +2517,7 @@
     stmt_ty p;
     if (!test) {
         PyErr_SetString(PyExc_ValueError,
-                        "field test is required for Assert");
+                        "field 'test' is required for Assert");
         return NULL;
     }
     p = (stmt_ty)PyArena_Malloc(arena, sizeof(*p));
@@ -2612,7 +2610,7 @@
     stmt_ty p;
     if (!value) {
         PyErr_SetString(PyExc_ValueError,
-                        "field value is required for Expr");
+                        "field 'value' is required for Expr");
         return NULL;
     }
     p = (stmt_ty)PyArena_Malloc(arena, sizeof(*p));
@@ -2682,7 +2680,7 @@
     expr_ty p;
     if (!op) {
         PyErr_SetString(PyExc_ValueError,
-                        "field op is required for BoolOp");
+                        "field 'op' is required for BoolOp");
         return NULL;
     }
     p = (expr_ty)PyArena_Malloc(arena, sizeof(*p));
@@ -2705,12 +2703,12 @@
     expr_ty p;
     if (!target) {
         PyErr_SetString(PyExc_ValueError,
-                        "field target is required for NamedExpr");
+                        "field 'target' is required for NamedExpr");
         return NULL;
     }
     if (!value) {
         PyErr_SetString(PyExc_ValueError,
-                        "field value is required for NamedExpr");
+                        "field 'value' is required for NamedExpr");
         return NULL;
     }
     p = (expr_ty)PyArena_Malloc(arena, sizeof(*p));
@@ -2733,17 +2731,17 @@
     expr_ty p;
     if (!left) {
         PyErr_SetString(PyExc_ValueError,
-                        "field left is required for BinOp");
+                        "field 'left' is required for BinOp");
         return NULL;
     }
     if (!op) {
         PyErr_SetString(PyExc_ValueError,
-                        "field op is required for BinOp");
+                        "field 'op' is required for BinOp");
         return NULL;
     }
     if (!right) {
         PyErr_SetString(PyExc_ValueError,
-                        "field right is required for BinOp");
+                        "field 'right' is required for BinOp");
         return NULL;
     }
     p = (expr_ty)PyArena_Malloc(arena, sizeof(*p));
@@ -2767,12 +2765,12 @@
     expr_ty p;
     if (!op) {
         PyErr_SetString(PyExc_ValueError,
-                        "field op is required for UnaryOp");
+                        "field 'op' is required for UnaryOp");
         return NULL;
     }
     if (!operand) {
         PyErr_SetString(PyExc_ValueError,
-                        "field operand is required for UnaryOp");
+                        "field 'operand' is required for UnaryOp");
         return NULL;
     }
     p = (expr_ty)PyArena_Malloc(arena, sizeof(*p));
@@ -2795,12 +2793,12 @@
     expr_ty p;
     if (!args) {
         PyErr_SetString(PyExc_ValueError,
-                        "field args is required for Lambda");
+                        "field 'args' is required for Lambda");
         return NULL;
     }
     if (!body) {
         PyErr_SetString(PyExc_ValueError,
-                        "field body is required for Lambda");
+                        "field 'body' is required for Lambda");
         return NULL;
     }
     p = (expr_ty)PyArena_Malloc(arena, sizeof(*p));
@@ -2823,17 +2821,17 @@
     expr_ty p;
     if (!test) {
         PyErr_SetString(PyExc_ValueError,
-                        "field test is required for IfExp");
+                        "field 'test' is required for IfExp");
         return NULL;
     }
     if (!body) {
         PyErr_SetString(PyExc_ValueError,
-                        "field body is required for IfExp");
+                        "field 'body' is required for IfExp");
         return NULL;
     }
     if (!orelse) {
         PyErr_SetString(PyExc_ValueError,
-                        "field orelse is required for IfExp");
+                        "field 'orelse' is required for IfExp");
         return NULL;
     }
     p = (expr_ty)PyArena_Malloc(arena, sizeof(*p));
@@ -2892,7 +2890,7 @@
     expr_ty p;
     if (!elt) {
         PyErr_SetString(PyExc_ValueError,
-                        "field elt is required for ListComp");
+                        "field 'elt' is required for ListComp");
         return NULL;
     }
     p = (expr_ty)PyArena_Malloc(arena, sizeof(*p));
@@ -2915,7 +2913,7 @@
     expr_ty p;
     if (!elt) {
         PyErr_SetString(PyExc_ValueError,
-                        "field elt is required for SetComp");
+                        "field 'elt' is required for SetComp");
         return NULL;
     }
     p = (expr_ty)PyArena_Malloc(arena, sizeof(*p));
@@ -2938,12 +2936,12 @@
     expr_ty p;
     if (!key) {
         PyErr_SetString(PyExc_ValueError,
-                        "field key is required for DictComp");
+                        "field 'key' is required for DictComp");
         return NULL;
     }
     if (!value) {
         PyErr_SetString(PyExc_ValueError,
-                        "field value is required for DictComp");
+                        "field 'value' is required for DictComp");
         return NULL;
     }
     p = (expr_ty)PyArena_Malloc(arena, sizeof(*p));
@@ -2967,7 +2965,7 @@
     expr_ty p;
     if (!elt) {
         PyErr_SetString(PyExc_ValueError,
-                        "field elt is required for GeneratorExp");
+                        "field 'elt' is required for GeneratorExp");
         return NULL;
     }
     p = (expr_ty)PyArena_Malloc(arena, sizeof(*p));
@@ -2990,7 +2988,7 @@
     expr_ty p;
     if (!value) {
         PyErr_SetString(PyExc_ValueError,
-                        "field value is required for Await");
+                        "field 'value' is required for Await");
         return NULL;
     }
     p = (expr_ty)PyArena_Malloc(arena, sizeof(*p));
@@ -3029,7 +3027,7 @@
     expr_ty p;
     if (!value) {
         PyErr_SetString(PyExc_ValueError,
-                        "field value is required for YieldFrom");
+                        "field 'value' is required for YieldFrom");
         return NULL;
     }
     p = (expr_ty)PyArena_Malloc(arena, sizeof(*p));
@@ -3051,7 +3049,7 @@
     expr_ty p;
     if (!left) {
         PyErr_SetString(PyExc_ValueError,
-                        "field left is required for Compare");
+                        "field 'left' is required for Compare");
         return NULL;
     }
     p = (expr_ty)PyArena_Malloc(arena, sizeof(*p));
@@ -3075,7 +3073,7 @@
     expr_ty p;
     if (!func) {
         PyErr_SetString(PyExc_ValueError,
-                        "field func is required for Call");
+                        "field 'func' is required for Call");
         return NULL;
     }
     p = (expr_ty)PyArena_Malloc(arena, sizeof(*p));
@@ -3100,7 +3098,7 @@
     expr_ty p;
     if (!value) {
         PyErr_SetString(PyExc_ValueError,
-                        "field value is required for FormattedValue");
+                        "field 'value' is required for FormattedValue");
         return NULL;
     }
     p = (expr_ty)PyArena_Malloc(arena, sizeof(*p));
@@ -3141,7 +3139,7 @@
     expr_ty p;
     if (!value) {
         PyErr_SetString(PyExc_ValueError,
-                        "field value is required for Constant");
+                        "field 'value' is required for Constant");
         return NULL;
     }
     p = (expr_ty)PyArena_Malloc(arena, sizeof(*p));
@@ -3164,17 +3162,17 @@
     expr_ty p;
     if (!value) {
         PyErr_SetString(PyExc_ValueError,
-                        "field value is required for Attribute");
+                        "field 'value' is required for Attribute");
         return NULL;
     }
     if (!attr) {
         PyErr_SetString(PyExc_ValueError,
-                        "field attr is required for Attribute");
+                        "field 'attr' is required for Attribute");
         return NULL;
     }
     if (!ctx) {
         PyErr_SetString(PyExc_ValueError,
-                        "field ctx is required for Attribute");
+                        "field 'ctx' is required for Attribute");
         return NULL;
     }
     p = (expr_ty)PyArena_Malloc(arena, sizeof(*p));
@@ -3198,17 +3196,17 @@
     expr_ty p;
     if (!value) {
         PyErr_SetString(PyExc_ValueError,
-                        "field value is required for Subscript");
+                        "field 'value' is required for Subscript");
         return NULL;
     }
     if (!slice) {
         PyErr_SetString(PyExc_ValueError,
-                        "field slice is required for Subscript");
+                        "field 'slice' is required for Subscript");
         return NULL;
     }
     if (!ctx) {
         PyErr_SetString(PyExc_ValueError,
-                        "field ctx is required for Subscript");
+                        "field 'ctx' is required for Subscript");
         return NULL;
     }
     p = (expr_ty)PyArena_Malloc(arena, sizeof(*p));
@@ -3232,12 +3230,12 @@
     expr_ty p;
     if (!value) {
         PyErr_SetString(PyExc_ValueError,
-                        "field value is required for Starred");
+                        "field 'value' is required for Starred");
         return NULL;
     }
     if (!ctx) {
         PyErr_SetString(PyExc_ValueError,
-                        "field ctx is required for Starred");
+                        "field 'ctx' is required for Starred");
         return NULL;
     }
     p = (expr_ty)PyArena_Malloc(arena, sizeof(*p));
@@ -3260,12 +3258,12 @@
     expr_ty p;
     if (!id) {
         PyErr_SetString(PyExc_ValueError,
-                        "field id is required for Name");
+                        "field 'id' is required for Name");
         return NULL;
     }
     if (!ctx) {
         PyErr_SetString(PyExc_ValueError,
-                        "field ctx is required for Name");
+                        "field 'ctx' is required for Name");
         return NULL;
     }
     p = (expr_ty)PyArena_Malloc(arena, sizeof(*p));
@@ -3288,7 +3286,7 @@
     expr_ty p;
     if (!ctx) {
         PyErr_SetString(PyExc_ValueError,
-                        "field ctx is required for List");
+                        "field 'ctx' is required for List");
         return NULL;
     }
     p = (expr_ty)PyArena_Malloc(arena, sizeof(*p));
@@ -3311,7 +3309,7 @@
     expr_ty p;
     if (!ctx) {
         PyErr_SetString(PyExc_ValueError,
-                        "field ctx is required for Tuple");
+                        "field 'ctx' is required for Tuple");
         return NULL;
     }
     p = (expr_ty)PyArena_Malloc(arena, sizeof(*p));
@@ -3353,12 +3351,12 @@
     comprehension_ty p;
     if (!target) {
         PyErr_SetString(PyExc_ValueError,
-                        "field target is required for comprehension");
+                        "field 'target' is required for comprehension");
         return NULL;
     }
     if (!iter) {
         PyErr_SetString(PyExc_ValueError,
-                        "field iter is required for comprehension");
+                        "field 'iter' is required for comprehension");
         return NULL;
     }
     p = (comprehension_ty)PyArena_Malloc(arena, sizeof(*p));
@@ -3416,7 +3414,7 @@
     arg_ty p;
     if (!arg) {
         PyErr_SetString(PyExc_ValueError,
-                        "field arg is required for arg");
+                        "field 'arg' is required for arg");
         return NULL;
     }
     p = (arg_ty)PyArena_Malloc(arena, sizeof(*p));
@@ -3439,7 +3437,7 @@
     keyword_ty p;
     if (!value) {
         PyErr_SetString(PyExc_ValueError,
-                        "field value is required for keyword");
+                        "field 'value' is required for keyword");
         return NULL;
     }
     p = (keyword_ty)PyArena_Malloc(arena, sizeof(*p));
@@ -3460,7 +3458,7 @@
     alias_ty p;
     if (!name) {
         PyErr_SetString(PyExc_ValueError,
-                        "field name is required for alias");
+                        "field 'name' is required for alias");
         return NULL;
     }
     p = (alias_ty)PyArena_Malloc(arena, sizeof(*p));
@@ -3477,7 +3475,7 @@
     withitem_ty p;
     if (!context_expr) {
         PyErr_SetString(PyExc_ValueError,
-                        "field context_expr is required for withitem");
+                        "field 'context_expr' is required for withitem");
         return NULL;
     }
     p = (withitem_ty)PyArena_Malloc(arena, sizeof(*p));
@@ -3494,7 +3492,7 @@
     type_ignore_ty p;
     if (!tag) {
         PyErr_SetString(PyExc_ValueError,
-                        "field tag is required for TypeIgnore");
+                        "field 'tag' is required for TypeIgnore");
         return NULL;
     }
     p = (type_ignore_ty)PyArena_Malloc(arena, sizeof(*p));
@@ -4602,11 +4600,8 @@
         case Del:
             Py_INCREF(astmodulestate_global->Del_singleton);
             return astmodulestate_global->Del_singleton;
-        default:
-            /* should never happen, but just in case ... */
-            PyErr_Format(PyExc_SystemError, "unknown expr_context found");
-            return NULL;
     }
+    Py_UNREACHABLE();
 }
 PyObject* ast2obj_boolop(boolop_ty o)
 {
@@ -4617,11 +4612,8 @@
         case Or:
             Py_INCREF(astmodulestate_global->Or_singleton);
             return astmodulestate_global->Or_singleton;
-        default:
-            /* should never happen, but just in case ... */
-            PyErr_Format(PyExc_SystemError, "unknown boolop found");
-            return NULL;
     }
+    Py_UNREACHABLE();
 }
 PyObject* ast2obj_operator(operator_ty o)
 {
@@ -4665,11 +4657,8 @@
         case FloorDiv:
             Py_INCREF(astmodulestate_global->FloorDiv_singleton);
             return astmodulestate_global->FloorDiv_singleton;
-        default:
-            /* should never happen, but just in case ... */
-            PyErr_Format(PyExc_SystemError, "unknown operator found");
-            return NULL;
     }
+    Py_UNREACHABLE();
 }
 PyObject* ast2obj_unaryop(unaryop_ty o)
 {
@@ -4686,11 +4675,8 @@
         case USub:
             Py_INCREF(astmodulestate_global->USub_singleton);
             return astmodulestate_global->USub_singleton;
-        default:
-            /* should never happen, but just in case ... */
-            PyErr_Format(PyExc_SystemError, "unknown unaryop found");
-            return NULL;
     }
+    Py_UNREACHABLE();
 }
 PyObject* ast2obj_cmpop(cmpop_ty o)
 {
@@ -4725,11 +4711,8 @@
         case NotIn:
             Py_INCREF(astmodulestate_global->NotIn_singleton);
             return astmodulestate_global->NotIn_singleton;
-        default:
-            /* should never happen, but just in case ... */
-            PyErr_Format(PyExc_SystemError, "unknown cmpop found");
-            return NULL;
     }
+    Py_UNREACHABLE();
 }
 PyObject*
 ast2obj_comprehension(void* _o)