Nested Scopes ... next tail recursion?

[Richard Davies]

> I wonder if there is any chance of getting
> tail recusion handled properly in the future?

Well, regardless of the language, you can write it yourself.

Consider a recursive function:

def recursivefunction(i):
   if i==0:
      return "bottom"
   else:
      return recursivefunction(i-1)

On my system this works for small i, but the
stack overflows by i=1000.


We now make the definition (attempting to support making
fairly general functions with fairly general argument lists
tail recursive):

from __future__ import nested_scopes
from types import DictType

def tailrecursedef(f):
   def g(*a, **b):
      r = apply(f, a, b)
      while type(r)==DictType and r.has_key('tailrecurse'):
         r = apply(f, r['tailrecurse'][0], r['tailrecurse'][1])
      else:
         return r
   return g


following which we can rewrite in tail recursive form:

def bit(i):
   if i==0:
      return "bottom"
   else:
      return {'tailrecurse': ((i-1,),{})}

tailrecursivefunction = tailrecursedef(bit)


and tailrecursivefunction(100000) is fine!

Richard.