How does your favorite language handle deep recursion? [closed]

Answer 1

Running ruby 1.9.2dev (2010-07-11 revision 28618) [x86_64-darwin10.0.0] on an older white macbook:

def f
  @i += 1
  f
end

@i = 0

begin
  f
rescue SystemStackError
  puts @i
end

outputs 9353 for me, meaning Ruby craps out with fewer than 10,000 calls on the stack.

With cross-recursion, such as:

def f
  @i += 1
  g
end

def g
  f
end

it craps out in half the time, at 4677 (~= 9353 / 2).

I can squeeze out a few more iterations by wrapping the recursive call in a proc:

def f
  @i += 1
  yield
end

@i = 0
@block = lambda { f(&@block) }

begin
  f(&@block)
rescue SystemStackError
  puts @i
end

which gets up to 4850 before erroring out.