taskPool.reduce vs algorithm.reduce

[Dorian Haglund via Digitalmars-d-learn]

Hi.

I'm trying to use taskPool.reduce with a delegate, for example:
import std.parallelism;

int main(string[] args)
{
  int f(int a, int b)
  {
    if (args.length > 1)
      return a+b;
    else
      return a-b;
  }

  auto res = taskPool.reduce!f([1, 2, 3]);

  return 0;
}

But it fails to compile (with gdc 8.1.0, dmd v2.081) complaining 
that

template instance reduce!(f) cannot use local 'f' as parameter to 
non-global template reduce(functions...)

The snippet above compiles with the reduce function from 
std.algorithm.

Is there a way to make the code compile with taskPool.reduce ?
(I don't want to write two functions and choosing one depending 
on args.length)

Why the interface difference between std.algorithm's reduce and 
taskPool.reduce ?

Best regards,

Dorian