aioobe aioobe - 3 months ago 10
Scala Question

Anonymous recursive function in Scala

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.