[Haskell-beginners] find problem

Hello, Sorry for asking so much but I really want to understand this. I have the function find k t [v, (k',v') <- t,k = v] Let's say k = false and t = [false, true, false, true] Then It will be find "false" ["false", "true", "false", "true] But where on earth are t,k = v and (k', v') come from ? Roelof