aioobe - 3 months ago 10

Scala Question

Is there a way to write an anonymous function that is recursive in Scala? I'm thinking of something like this:

`((t: Tree) => {`

print(t.value);

for (c <- t.children)

thisMethod(c)

})(root)

(Related question: Which languages support *recursive* function literals / anonymous functions?)

Answer

As described in the link you posted. You can use Y-combinator. Here is example:

```
scala> def fix[A,B](f: (A=>B)=>(A=>B)): A=>B = f(fix(f))(_)
fix: [A,B](f: ((A) => B) => (A) => B)(A) => B
scala> val fact = fix[Int,Int](f => a => if(a<=0) 1 else f(a-1) * a)
fact: (Int) => Int = <function1>
scala> fact(12)
res0: Int = 479001600
```

Note it doesn't work with big numbers. Be careful with tail call optimization.