Starting to try to move some functions away from Evaluator.

This time eval_trailer.

jedi/evaluate/syntax_tree.py

@@ -0,0 +1,27 @@
+"""
+Functions evaluating the syntax tree.
+"""
+
+from jedi import debug
+
+
+def eval_trailer(context, base_contexts, trailer):
+    trailer_op, node = trailer.children[:2]
+    if node == ')':  # `arglist` is optional.
+        node = ()
+
+    if trailer_op == '[':
+        from jedi.evaluate import iterable
+        return iterable.py__getitem__(context.evaluator, context, base_contexts, trailer)
+    else:
+        debug.dbg('eval_trailer: %s in %s', trailer, base_contexts)
+        if trailer_op == '.':
+            return base_contexts.py__getattribute__(
+                name_context=context,
+                name_or_str=node
+            )
+        else:
+            assert trailer_op == '('
+            from jedi.evaluate import param
+            arguments = param.TreeArguments(context.evaluator, context, node, trailer)
+            return base_contexts.execute(arguments)