# HG changeset patch
# User Aurelien Campeas <aurelien.campeas@gmail.com>
# Date 1392503796 -3600
#      Sat Feb 15 23:36:36 2014 +0100
# Node ID 9b591f345b4898bdaaf2a19b962ebb90678d1f1e
# Parent  84e34cc7d1bd433abcefc9dcd0a0815e43414a07
dispatch: unroll mro computation to make it more palatable

diff --git a/dispatch.py b/dispatch.py
--- a/dispatch.py
+++ b/dispatch.py
@@ -19,15 +19,26 @@
 def clos_mro(types_func_map, callsig):
     """ David Mertz's clos mro """
     siglen = len(callsig)
-    table = [(sig, func) for sig, func in types_func_map.iteritems()
-             if len(sig) == siglen
-             and reduce(mul, map(issubclass, callsig, sig))]
+    # table of signature -> function
+    # matching the call signature
+    table = []
+    for signature, func in types_func_map.iteritems():
+        if len(signature) != siglen:
+            continue
+        for callklass, sigklass in zip(callsig, signature):
+            if not issubclass(callklass, sigklass):
+                break
+        else:
+            table.append((signature, func))
     mros = tuple(klass.__mro__ for klass in callsig)
     if len(check_ambiguity(table, mros)) > 1:
         raise TypeError("ambigous call; types=%r; candidates=%r" %
                         (types_func_map, table))
-    return (x[1] for x in sorted((map(proximity, sig, mros), func)
-                  for sig, func in table))
+    sorter = []
+    for signature, func in table:
+        sorter.append((map(proximity, signature, mros), func))
+    sorter.sort()
+    return [elt[1] for elt in sorter]
 
 
 class NoNextMethod(Exception): pass