Question

My code:

def power(x: Double, n: Int): Double = {
  if (n % 2 == 0 && n > 0) power(power(x, n/2), 2)
  else if (n % 2 == 1 && n > 0) x * power(x, n - 1)
  else if (n == 0) 1
  else if (n < 0) 1 / power(x, -n)
}

println(power(2, 2))

Terminal:

$ scala ch2ex10.scala 
/scala/impatient/ch2ex10.scala:5: error: type mismatch;
 found   : Unit
 required: Double
  else if (n < 0) 1 / power(x, -n)

Where is this Unit coming from?

Thanks!

Answer 1

It comes from the last “else if” in the block.

It doesn’t look like all possibilities are exhausted. If there is no other possibility left (which happens to be the case here), just write

 else 1 / power(x, -n)

if another possibility would be open, you would need to write

 else if (n < 0) 1 / power(x, -n)
 else ...

and fill out the dots. Else the compiler assumes

 else {}

for you.