Solutions to the week 3 homework exercises in Brent Yorgey's 2013 offering of cis194. The focus of this week was to use higher order functions and move away from heavy usage of recursion and pattern matching.
These solutions use the (.) function which had not yet been coverered at this point in the course. You can find plenty
of information about comopse on the interwebs and can of course start your investigation in ghci with :t (.).
| module Week03.Golf | |
| ( skips | |
| , localMaxima | |
| , histogram | |
| , histogramGen | |
| ) where | |
| skips :: [a] -> [[a]] | |
| skips xs = map (`everyNth` xs) [1..(length xs)] | |
| where everyNth n = map snd . filter ((==0) . (`mod` n) . fst) . zip [1..] | |
| localMaxima :: [Integer] -> [Integer] | |
| localMaxima = map (\(_, x, _) -> x) . filter (\(x, y, z) -> y > x && y > z) . triples | |
| where | |
| triples (x:y:z:rs) = (x,y,z) : triples (y:z:rs) | |
| triples _ = [] | |
| -- general version that allows for any domain, not just 0..9 | |
| -- e.g. putStr (histogramGen [0..3] [0,0,1,2,2,2,3]) | |
| histogramGen :: [Integer] -> [Integer] -> String | |
| histogramGen domain xs = | |
| let | |
| freq n = length . filter (== n) | |
| freqs = map (`freq` xs) domain | |
| buildRow n = map (\f -> if f >= n then '*' else ' ') freqs | |
| rows = map buildRow (reverse [1..(maximum freqs)]) | |
| separator = take (length domain) (repeat '=') | |
| legend = foldl (++) "" (map show domain) | |
| in | |
| unlines (rows ++ [separator, legend]) | |
| histogram :: [Integer] -> String | |
| histogram = histogramGen [0..9] |