Explain function syntax

[Brother Bill via Digitalmars-d-learn]

In the following from Programming in D, page 483, we use function 
keyword.

I expect that the first int in
```
int function(int);
```
represents the return value.

What does the second (int) refer to?

Then there is another example with 'delegate' instead of 
'function.

```
import std.stdio;

void main()
{

}

alias Calculator = int function(int);

Calculator makeCalculator()
{
        int increment = 10;
        return value => increment + value; // ← compilation ERROR
}

```