weird-adder.hs

-- weird-adder.hs - Josh Sandlin - 6:45PM - 2/14/2010
-- Really weird way to add a range of numbers

-- takes an upper limit and returns a list of pairs
pairedRange :: Int -> [(Int, Int)]
pairedRange x = zip [ a | a <- [1..x], odd a ] [ b | b <- [1..x], even b ]

-- adds a list of pairs
addPairs :: (Num a) => [(a, a)] -> [a]
addPairs x = [ a + b | (a, b) <- x ]

-- takes a number, builds a range, adds the pairs, then sums the list
sumPairedRange :: Int -> Int
sumPairedRange x = sum (addPairs (pairedRange x))

sum' :: Int -> Int
sum' x = sumPairedRange x

-- sum [1..20] => 210
-- sum' 20     => 210 <- 20 is the upper limit of the range