Define AST nodes and instruction transformations.

Enable syntax: iadd(x, y) which creates an Apply node.
Enable syntax: z << iadd(x, y) which creates a Def node.

Add an XForm class which represents source and destination patterns as
RTL lists.

meta/cretonne/test_ast.py

@@ -0,0 +1,28 @@
+from __future__ import absolute_import
+from unittest import TestCase
+from doctest import DocTestSuite
+from . import ast
+from .base import jump, iadd
+
+
+def load_tests(loader, tests, ignore):
+    tests.addTests(DocTestSuite(ast))
+    return tests
+
+
+x = 'x'
+y = 'y'
+a = 'a'
+
+
+class TestPatterns(TestCase):
+    def test_apply(self):
+        i = jump(x, y)
+        self.assertEqual(repr(i), "Apply(jump, ('x', 'y'))")
+
+        i = iadd.i32(x, y)
+        self.assertEqual(repr(i), "Apply(iadd.i32, ('x', 'y'))")
+
+    def test_single_ins(self):
+        pat = a << iadd.i32(x, y)
+        self.assertEqual(repr(pat), "('a',) << Apply(iadd.i32, ('x', 'y'))")