Faulhaber's triangle: Difference between revisions

{{works with|GHC|7.10.3}}

import Control.Arrow ((&&&))

-- FAULHABER -------------------------------------------------------------------

-- DISPLAY ---------------------------------------------------------------------

-- (Max numerator+denominator widths) -> Column width -> Filler -> Ratio -> String

justifyRatio :: (Int, Int) -> Int -> Char -> Rational -> String

justifyRatio (wn, wd) n c nd =

let [num, den] = [numerator, denominator] <*> [nd]

w = max n (wn + wd + 2) -- Minimum column width, or more if specified.

in if 1 == den

then center w c (show num)

else let (q, r) = quotRem (w - 1) 2

in concat

[ justifyRight q c (show num)

, "/"

, justifyLeft (q + r) c (show den)

]

center, justifyLeft, justifyRight :: Int -> Char -> String -> String

center n c s =

let (q, r) = quotRem (n - length s) 2

in concat [replicate q c, s, replicate (q + r) c]

justifyLeft n c s = take n (s ++ replicate n c)

justifyRight n c s = drop (length s) (replicate n c ++ s)

-- List of Ratios -> (Max numerator width, Max denominator width)

maxWidths :: [[Rational]] -> (Int, Int)

maxWidths xss =

let widest f xs = maximum $ fmap (length . show . f) xs

in widest numerator &&& widest denominator $ concat xss

-- TEST ------------------------------------------------------------------------

]</lang>