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scalarecursionanonymous-function

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?)

Solution

  • 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.