Attaching a block to []

Hello,

Talking to Tilman Sauerbeck on IRC lead me to an interesting bug in
ruby. The following code gives a syntax error using both 1.8.2 and my
recent build of 1.9:

class Hash
    alias_method :orig_lookup, :[]

    def [](key)
        value = self.orig_lookup(key)
        block_given? ? (yield value) : value
    end
end

Foo = { :key => :value }

Foo[:key] do |v| # Syntax Error!
    p v
end

As you can see the code is trying to yield the lookup on the hash
table if a block was passed. Running the code will simply not let the
block be passed unless you make this change:

Foo.[](:key) do |v| # No syntax error.

I would hope that this could be fixed so the first case would work.

Thank you for your time.

Brian.