Explain function syntax

[kdevel]

On Wednesday, 17 September 2025 at 22:16:50 UTC, Brother Bill 
wrote:
> 	return value => increment + value; // ← compilation ERROR

```d
void main()
{
	auto calc = makeCalculator;
	writeln (calc (1));
}

alias Calculator = int function(int);

Calculator makeCalculator()
{
	enum increment = 10; // must not be a stack var
	return value => increment + value;
}

import std.stdio;
```

Compiles and prints 11.