appendFile package:xmonad-contrib

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]])
A prompt for appending a single line of text to a file. Useful for keeping a file of notes, things to remember for later, and so on--- using a keybinding, you can write things down just about as quickly as you think of them, so it doesn't have to interrupt whatever else you're doing. Who knows, it might be useful for other purposes as well!
Given an XPrompt configuration and a file path, prompt the user for a line of text, and append it to the given file.
Given an XPrompt configuration, string transformation function and a file path, prompt the user for a line of text, transform it and append the result to the given file.