[erlang-questions] newbie question of if guards

[Chris Rathman]

Thanks for the answers (from Mathias and Kostis)!  That gets me further 
along. 

As long as I'm asking annoying newbie questions and I'm on the pedagogic 
subject of square roots....  :-)

I'm trying to figure out the way Erlang does nested functions.  From 
what I gather, anonymous functions would be the way to go.  
Unfortunately, I can't figure out how to make the lambda functions be 
recursive, and searches for 'Erlang' and 'fun' don't narrow it down 
enough.  Here's what I am trying to do:

sqrt(X) ->
   Good_Enough =
      fun (Guess) ->
         abs(square(Guess) - X) < 0.001
      end,

   Improve =
      fun (Guess) ->
         average(Guess, X / Guess)
      end,

   Sqrt_Iter =
      fun (Guess) ->
         case (Good_Enough(Guess)) of
            true -> Guess;
            false -> Sqrt_Iter(Improve(Guess))
         end
      end,

   Sqrt_Iter(1.0, X).

The recursive call in Sqrt_Iter gives me an error informing me that it 
is unbound.  I can understand why it is unbound, but I was wondering if 
there's something similar to CaML's 'rec' modifier?  Or is there another 
Erlang idiom for achieving this effect?

Thanks,
Chris Rathman

Matthias Lang wrote:
> Erlang does not allow calling arbitrary functions from guards.
>
> One way to achieve what you're attempting below is to use 'case'
> instead:
> ....
> Matthias
>
>
>