Function To Call Function By Name Given As Parameter

I want to write function to call another function which name is
parameter to first function. Other parameters should be passed to
called function.
If I call it function('f1',10) it should call f1(10). If I call it
function('f2',5) it should call f2(5).

So far i tried something like

CREATE FUNCTION [dbo].[func] (@f varchar(50),@m money)
RETURNS varchar(50) AS
BEGIN
return(select 'dbo.'+@f+'('+convert(varchar(50),@m)+')')
END

When I call it select dbo.formuła('f_test',1000) it returns
'select f_test(1000)', but not value of f_test(1000).

What's wrong?

Mariusz