Choosing data from a list of tuples in Haskell.

Answer 1

You can use maximumBy with comparing:

module Main where

import Data.Ord (comparing)
import Data.List (maximumBy)

findMaxVal :: (Num a, Ord a, Num b, Ord b) => [((a, b), (a, b), (a, b))] -> b
findMaxVal = xWidth . maximumBy (comparing tWidth)
  where
    xWidth ((_, x1), (_, x2), _) = x2 - x1
    tWidth ((t1, _), _, (t3, _)) = t3 - t1