Sending arguments to filter methods


I want to set up a before_filter, and I want to be able to pass it
some parameters. My method looks like

def my_filter(a)


And I want to do

before_filter :myfilter ‘a’

I’ve tried the above and
before_filter :myfilter, ‘a’

but neither one is acceptable. How can I specify an argument to pass
in to the filter method?