Why does the function go into an infinite cycle?

[Anatoli Sakhnik]

Hello!
Can anyone tell me what's wrong in the following function. I select
something, press \/, enter _graph on the prompt and get another prompt
immediately...

function! VisualRangeSearch(flags)
    let pat = input("'<,'>/")
    let s = '\%V'.pat
    call search(s, a:flags)
endf

vnoremap <Leader>/ :call VisualRangeSearch('')
vnoremap <Leader>? :call VisualRangeSearch('b')

-- Anatoli Sakhnik