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]]

I actually want to shorten this part:

 | cr1 <- colors,
   cr2 <- colors,
   cr3 <- colors,
   cr4 <- colors,
   cr5 <- colors,

to something like (cr1, cr2, cr3, cr4, cr5) <- colors. Any suggestions to do that?

You could make different list comprehensions to solve it more clear. For example:

getC2and4s = [(c2,c4) | cr2 <- colors, cr4 <- colors]

getC234s = [  (c2,c3,c4) | c3 <- colors, (c2,c4) <- getC2and4s, myCheck]

getC12345s = ...

In the end I would map the tuple with 5 colors to the tuples with state names. Something with the signature

colorsWithStates :: (Color,Color,Color,Color,Color) -> (StateColor, StateColor, StateColor,StateColor,StateColor)

To introduce StateColor you should look into the type keyword.

I think you will get the idea. Otherwise you can always contacts me.

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.