Lambda recursive ...
Olexandr Demura
oleksander.demura at gmail.com
Sat Oct 20 12:53:12 PDT 2012
Or choose to be even more functional (-: replace recursion with
fixed-point combinator.
interface PreIntToInt {
int apply(PreIntToInt next, int i);
default IntToInt fix() { return (i) -> { return this.apply(this, i); }
}
PreIntToInt preFactorial = (self, i) -> { return i == 0 ? 1 : i *
self.apply(i - 1); };
IntToInt factorial = preFactorial.fix();
Have a nice weekend.
2012/10/20 Remi Forax <forax at univ-mlv.fr>:
> On 10/20/2012 06:29 PM, Maurice Naftalin wrote:
>> The FAQ page with this factorial example
>> (http://lambdafaq.org/can-lambda-expressions-be-used-to-define-recursive-functions/)
>> actually did make that point. It makes it more emphatically now.
>
> You can also define the recursive function and use the method referene
> syntax:
> class A {
> static int fibo(int n) {
> return (n < 2)? 1: fibo(n -1) + fibo(n - 2);
> }
> ...
> Mapper<Integer, Integer> mapper = A#fibo;
> }
>
> Rémi
>>
>> Maurice
>>
>> On 19/10/2012 14:18, Aleksey Shipilev wrote:
>>> On 10/19/2012 05:09 PM, Boaz Nahum wrote:
>>>
>>>> interface FactInt { int invoke(int i); }
>>>>
>>>> FactInt factorial = i ->
>>>> { return i == 0 ? 1 : i * factorial.invoke(i - 1); };
>>>>
>>>> But the compile (b61) says:
>>>> error: variable factorial might not have been initialized
>>>>
>>>> How can I write recursive expression like this ?
>>>>
>>> Lambda can not capture the uninitialized local variable; the trick is to
>>> use fields, in which case lambda will capture "this" or the reference to
>>> static field [1].
>>>
>>> -Aleksey.
>>>
>>> [1]
>>> https://github.com/shipilev/jdk8-lambda-samples/blob/master/src/test/java/net/openjdk/lambda/FibonacciTest.java
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