Welcome back to Haskell Function of the Day! Today we'll talk about cute little function in
Prelude that can be useful for processing text: 'words'. It takes a string and breaks it into
words delimited by white space. It returns a list of strings where each item in the string is a
particular word. For example

> words "This is a test"
["This","is","a","test"]

One thing to keep in mind is that 'words' regards punctuation marks as part of the words to
which they are attached... or even as separate words entirely.

> words "This, my friend, is a test !"
["This,","my","friend,","is","a","test","!"]

Notice the trailing commas on "This," and "friend," and notice that the final '!' is a word by
itself (due to the space separating it from "test" in the original string). Sophisticated text
processing applications would probably find this behavior a little simplistic so some
preprocessing or post processing might be necessary.

There is a corresponding 'unwords' function that does the reverse of 'words.' Thus

> unwords ["This", "is", "a", "test"]
"This is a test"

The cool part is that you can combine these functions with other list handling techniques.

> let sentence = "This is a test"
> length (words sentence)
4
> (words sentence) !! 3
"test"
> unwords (reverse (words sentence))
"test a is This"

Be sure you understand why these results are produced. Notice the difference between the last
example and

> reverse sentence
"tset a si sihT"

And, of course, pattern matching works.

> let (firstWord:remainingWords) = words sentence
> firstWord
"This"
> unwords remainingWords
"is a test"

That's it for today's edition of Haskell Function of the Day. I hope you enjoyed it!

Peter