Local functions

[Mark Mahieu]

On 10 Feb 2010, at 15:05, Rémi Forax wrote:

> Le 10/02/2010 14:52, Mark Mahieu a écrit :
>> On 10 Feb 2010, at 13:09, Rémi Forax wrote:
>>   
>>> There is a simple solution, if you want to write recursive function,
>>> create a static method
>>> and reference it as a lambda:
>>> 
>>> class A {
>>>   static int factorial(int x) {
>>>     return (x<= 1) ? 1 : x*factorial.(x-1);
>>>   }
>>> 
>>>      public static void main(String[] args) {
>>>          #int(int) lambda = A#factorial;
>>>      }
>>> }
>>> 
>>>     
>> I don't think that approach is quite so simple if your recursive function needs to use locals in the method which 'creates' it (eg. it references 'args' in 'main', in your example).
>> 
>> Regards,
>> 
>> Mark
>>   
> 
> In that case, the anonymous class syntax is your friend.
> 
> Or if lambdas are translated to method handles, you can write:
> 
> class A {
>  static int foo(String[] args, int x) {
>    return (x<= 1) ? args.length : x*foo.(x-1);
>  }
> 
>  public static void main(String[] args) {
>    #int(int) lambda = A#foo.bindTo(args);
>  }
> }
> 
> cheers,
> Rémi
> 
> 


You *can* do it without method references, method handles, or partial application too.  But you mentioned a simple solution, which to me suggests an ideal of being able to 'create' the lambda in approximately the same manner regardless of whether it's recursive or references local variables.

Anyway, we could do with finding some additional recursive examples - factorial is getting worn out ;-)  One which I frequently write involves walking a tree and doing something with (eg. collecting) all nodes which match some criteria.  I'm slightly surprised it didn't crop up in the recent codebase stats I submitted though... I might look into why that is.


Cheers,

Mark