Add type variables.

cranelift/docs/metaref.rst

@@ -38,3 +38,13 @@ Predefined types
 .. automodule:: cretonne.types
     :members:
 
+Parametric polymorphism
+-----------------------
+.. currentmodule:: cretonne
+
+Instruction operands can be defined with *type variables* instead of concrete
+types for their operands. This makes the instructions polymorphic.
+
+.. autoclass:: TypeVar
+
+

meta/cretonne/__init__.py

@@ -94,3 +94,19 @@ class FloatType(ScalarType):
 
     def __repr__(self):
         return 'FloatType(bits={})'.format(self.bits)
+
+#
+# Parametric polymorphism.
+#
+
+class TypeVar(object):
+    """
+    A Type Variable.
+
+    Type variables can be used in place of concrete types when defining
+    instructions. This makes the instructions *polymorphic*.
+    """
+
+    def __init__(self, name):
+        self.name = name
+