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4.22: How do I expand function calls in a string?

    (contributed by brian d foy)

    This is documented in perlref, and although it's not the easiest thing
    to read, it does work. In each of these examples, we call the function
    inside the braces used to dereference a reference. If we have more than
    one return value, we can construct and dereference an anonymous array.
    In this case, we call the function in list context.

            print "The time values are @{ [localtime] }.\n";

    If we want to call the function in scalar context, we have to do a bit
    more work. We can really have any code we like inside the braces, so we
    simply have to end with the scalar reference, although how you do that
    is up to you, and you can use code inside the braces. Note that the use
    of parens creates a list context, so we need "scalar" to force the
    scalar context on the function:

            print "The time is ${\(scalar localtime)}.\n"

            print "The time is ${ my $x = localtime; \$x }.\n";

    If your function already returns a reference, you don't need to create
    the reference yourself.

            sub timestamp { my $t = localtime; \$t }

            print "The time is ${ timestamp() }.\n";

    The "Interpolation" module can also do a lot of magic for you. You can
    specify a variable name, in this case "E", to set up a tied hash that
    does the interpolation for you. It has several other methods to do this
    as well.

            use Interpolation E => 'eval';
            print "The time values are $E{localtime()}.\n";

    In most cases, it is probably easier to simply use string concatenation,
    which also forces scalar context.

            print "The time is " . localtime() . ".\n";

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