diff --git a/artiq/py2llvm/base_types.py b/artiq/py2llvm/base_types.py
index a922a2d75..f34646cf6 100644
--- a/artiq/py2llvm/base_types.py
+++ b/artiq/py2llvm/base_types.py
@@ -4,19 +4,9 @@ from artiq.py2llvm.values import VGeneric
 
 
 class VNone(VGeneric):
-    def __repr__(self):
-        return "<VNone>"
-
     def get_llvm_type(self):
         return lc.Type.void()
 
-    def same_type(self, other):
-        return isinstance(other, VNone)
-
-    def merge(self, other):
-        if not isinstance(other, VNone):
-            raise TypeError
-
     def alloca(self, builder, name):
         pass
 
@@ -52,7 +42,8 @@ class VInt(VGeneric):
             if other.nbits > self.nbits:
                 self.nbits = other.nbits
         else:
-            raise TypeError
+            raise TypeError("Incompatible types: {} and {}"
+                            .format(repr(self), repr(other)))
 
     def set_value(self, builder, n):
         self.set_ssa_value(
@@ -160,15 +151,9 @@ class VBool(VInt):
     def __init__(self):
         VInt.__init__(self, 1)
 
-    def __repr__(self):
-        return "<VBool>"
-
-    def same_type(self, other):
-        return isinstance(other, VBool)
-
-    def merge(self, other):
-        if not isinstance(other, VBool):
-            raise TypeError
+    __repr__ = VGeneric.__repr__
+    same_type = VGeneric.same_type
+    merge = VGeneric.merge
 
     def set_const_value(self, builder, b):
         VInt.set_const_value(self, builder, int(b))
diff --git a/artiq/py2llvm/fractions.py b/artiq/py2llvm/fractions.py
index 7bf652c73..498a916e8 100644
--- a/artiq/py2llvm/fractions.py
+++ b/artiq/py2llvm/fractions.py
@@ -70,16 +70,6 @@ class VFraction(VGeneric):
     def get_llvm_type(self):
         return lc.Type.vector(lc.Type.int(64), 2)
 
-    def __repr__(self):
-        return "<VFraction>"
-
-    def same_type(self, other):
-        return isinstance(other, VFraction)
-
-    def merge(self, other):
-        if not isinstance(other, VFraction):
-            raise TypeError
-
     def _nd(self, builder):
         ssa_value = self.get_ssa_value(builder)
         a = builder.extract_element(
diff --git a/artiq/py2llvm/values.py b/artiq/py2llvm/values.py
index 711b0cdb9..e5536181a 100644
--- a/artiq/py2llvm/values.py
+++ b/artiq/py2llvm/values.py
@@ -7,6 +7,17 @@ class VGeneric:
     def __init__(self):
         self._llvm_value = None
 
+    def __repr__(self):
+        return "<" + self.__class__.__name__ + ">"
+
+    def same_type(self, other):
+        return isinstance(other, self.__class__)
+
+    def merge(self, other):
+        if not self.same_type(other):
+            raise TypeError("Incompatible types: {} and {}"
+                            .format(repr(self), repr(other)))
+
     def get_ssa_value(self, builder):
         if isinstance(self._llvm_value, lc.AllocaInstruction):
             return builder.load(self._llvm_value)