CODEWITHSUNDEEP
scalalambda
Xolve
Xolve

Reputation: 23220

What is wrong with use of lambda here

I wrote map1 function similar to List.map as:

def map1[A, B](xs: List[A], f: A => B): List[B] = {
  xs match {
    case List() => scala.collection.immutable.Nil
    case head :: tail => f(head) :: map1(tail, f)
  }
}

Now when I call the above as:

map1(List(1, 2, 3), x => x + 1)

I get error as: error: missing parameter type. But following works:

List(1, 2, 3).map(x => x + 1)

Why map1 doesn't work with lamdas?

Upvotes: 1

Views: 80

Answers (1)

Yuval Itzchakov
Yuval Itzchakov

Reputation: 149626

In Scala, argument type inference works between argument lists and not inside them. To help the compiler infer the type, move f to it's own argument list:

def map1[A, B](xs: List[A])(f: A => B): List[B] = {
  xs match {
    case Nil => scala.collection.immutable.Nil
    case head :: tail => f(head) :: map1(tail)(f)
  }
}

Upvotes: 4

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