The computation appendFile file str function appends the string str, to the file file.
Note that writeFile and appendFile write a literal string to a file. To write a value of any printable type, as with print, use the show function to convert the value to a string first.
> main = appendFile "squares" (show [(x,x*x) | x <- [0,0.1..2]])
Write a string the end of a file.