functions.barrett

var
    X, Y;
function ExecuteFunction(f, param);
    begin
        f(param);
    end;

function Print(a);
    begin
        WriteLn(a);
    end;

function AddFive(x);
    begin
        WriteLn(x + 5);
    end;

function GetFunction(num);
    function PrintHello;
        begin
            WriteLn("Hello");
        end;

    function PrintGoodbye;
        begin
            WriteLn("Goodbye");
        end;

    begin
        if num = 1 then
        begin
            Result := @PrintHello;
        end
        else
        begin
            Result := @PrintGoodbye;
        end;
    end;


begin
    { Pass a function to another function }
    { '@' is placed in front of function name to pass without evaluating }
    ExecuteFunction(@Print, "Hello World");
    ExecuteFunction(@AddFive, 3);

    { Functions can be returned as well }
    X := 1;
    Y := GetFunction(X); { Should return a function that prints "Hello" }
    Y; { Executes the function returned by GetFunction }

    X := 2;
    Y := GetFunction(X); { Should return a function that prints "Goodbye" }
    Y; { Executes the function returned by GetFunction }

end;