tdlp: higher-order functions

[Jerome BENOIT]

Hello List:

In tDlp book in section 5.6 entitled `Higher-Order Functions. Function Literals,
the first code example is:

-----------------------------------------------------------------
T[] find(alias pred, T)(T[] input)
        if (is(typeof(pred(input[0])) == bool)) {
        for(; input.length > 0; input = input[1 .. $]) {
                if (pred(input[0])) break;
                }
        return input;
        }
-----------------------------------------------------------------

I can play it. Nevertheless, it is not clear for me right now
what is the role played by `T' in the generic argument list (alias pred, T).
(Its meaning is bypassed in this section via a `deduction' way.)

Any hint is welcome.

Thanks in advance,
Jerome