Type inference of Joy expressions.

More remains to be done but it seems to work.

joy/utils/stack.py

@@ -156,7 +156,7 @@ def concat(quote, expression):
   # RuntimeError: maximum recursion depth exceeded
   # on quotes longer than sys.getrecursionlimit().
 
-##  return (quote[0], concat(quote[1], expression)) if quote else expression
+  return (quote[0], concat(quote[1], expression)) if quote else expression
 
   # Original implementation.
 
@@ -165,13 +165,13 @@ def concat(quote, expression):
   # In-lining is slightly faster (and won't break the
   # recursion limit on long quotes.)
 
-  temp = []
-  while quote:
-    item, quote = quote
-    temp.append(item)
-  for item in reversed(temp):
-    expression = item, expression
-  return expression
+##  temp = []
+##  while quote:
+##    item, quote = quote
+##    temp.append(item)
+##  for item in reversed(temp):
+##    expression = item, expression
+##  return expression