bigrams.hs

import Data.Char 

x = "the quick brown fox jumps over the lazy dog"
y = "it was the best of times, it was the worst of times"
z = "to be or not to be"

bigrams :: [Char] -> [(Char,Char)]
-- generate a list of bigram pairs for a string
bigrams sentence = removeNonAlphaChars $ zip sentence $ tail sentence

removeNonAlphaChars :: [(Char,Char)] -> [(Char,Char)]
-- filter out bigrams that contain spaces, punctuation, etc
removeNonAlphaChars = filter $ \(x,y) -> isLetter x && isLetter y

insert :: Eq a => a -> [(a,Int)] -> [(a,Int)]
-- the list counts occurrences of a's
-- NOTE would be better to do this with a Data.Map
insert x [] = [(x,1)]
insert x ((y,count):rest) = if x==y then (y,count+1):rest
                                    else (y,count):(insert x rest)

freqlist :: Eq a => [a] -> [(a,Int)]
-- take list of elements, produce list of (element,count) pairs
-- NOTE would be better to do this with a Data.Map
freqlist elts = foldl (\lst elt -> insert elt lst) [] elts


-- now try something like:
-- freqlist $ bigrams z

and it would be nicer to define a newtype for Bigram too