[Python-ideas] Tail recursion elimination

[spir]

On 01/19/2014 12:09 AM, Terry Reedy wrote:

I share all your views except for the following, which in my view is incomplete:

> 1) A tail call is a 'top level' call in a return statement.
>      return f(*args, **kwds)
> A directly recursive call, where f refers to the function with the return
> statement, is a special case.

This is also true for "actions" (rather than proper functions, which purpose is 
to compute a new piece of data). It's actually rather common (also in C ;-). 
There is no data procuct. (see PS)

Denis

PS: An example may be an "action" writing out list items which calls, or rather 
delegates to, another action that writes additional items preceded by a separator.

def write_items (stream, l):
     n = len(l)
     if n == 0:
         stream.write('\n')
         return

     stream.write(str(l[0]))
     if n == 1 : return

     write_other_items(stream, l, n)	# tail call

def write_other_items (stream, l, n):
     for i in range(1,n):
         stream.write(" ")
         stream.write(str(l[i]))
     stream.write('\n')

from sys import stdout
l = []
write_items(stdout, l)
l = [1]
write_items(stdout, l)
l = [1,2,3]
write_items(stdout, l)