7 languages, Haskell, day 1, map-coloring

mapcoloring.hs

-- Author: Bart Groeneveld
-- License: GPLv3
module Main where

    data Color = Red
               | Green
               | Blue
               deriving (Eq, Show, Enum)
    colors = [Red ..]

    coloring = head [[("Tennessee"  , cr1),
                      ("Mississippi", cr2),
                      ("Alabama"    , cr3),
                      ("Georgia"    , cr4),
                      ("Florida"    , cr5)]
                     | cr1 <- colors,
                       cr2 <- colors,
                       cr3 <- colors,
                       cr4 <- colors,
                       cr5 <- colors,
                       cr1 `notElem` [cr2, cr3, cr4],
                       cr3 `notElem` [cr2,      cr4],
                       cr5 `notElem` [cr2, cr3, cr4]]

One more thing: Try to solve it in parts. You currently are trying to solve it in one big function, which makes it harder to reason about it IMO. Clearly c2 and c4 have no restrictions, thus you can extract those.