when I learn Haskell write some good examples to remember some special
- first-element's order number is 0
- ++ add list from left to the end
- : instanuously add list or just some expression in list
- !! get something out of list ( !! )
- there is a example show what different : ++ in haskell and how to use it smart 1:[]:[1,2,3] it's wrong but 1:[]++[1,2,3] it's true
- list can be compared if the element in list can be compared head take a list and return its head