4. List and String Manipulation Routines

In Haskell, strings are represented and treated as linked lists of characters. Thus, all the functions that operate on lists, operate on strings as well.
Here are some common routines:

Function Name	Description
`head`	The first element in the list
`tail`	The list containing the second to the other elements
`length`	The length of the list.
`reverse`	A list whose elements are reversed.
`take num_elems list`	Extracts a list with the first `num_elems` from `list`.
`drop num_elems list`	Extracts the list starting with the num_elems+1's element.
`filter callback list`	Extracts the list of elements that match a certain callback. A kin to `grep` in Perl.
`map callback list`	transforms each element in the list according to the callback
`a ++ b`	Concatenates the lists a and b