qzchenwl

{-# LANGUAGE TemplateHaskell #-}
{-# LANGUAGE OverloadedStrings #-}

module Main where

import qualified Data.ByteString.Char8 as B
import qualified Data.Text as T
import           Data.Maybe
import           Snap
import           Snap.Snaplet.Heist

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-- file: ch03/GrahamScan.hs

import Data.List
import Data.Ord

type Point = (Double, Double)

data Direction = LeftTurn
               | RightTurn
               | Straight

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import Control.Monad
import Data.Maybe

maybeToMonad :: (MonadPlus m) => Maybe a -> m a
maybeToMonad Nothing  = mzero
maybeToMonad (Just x) = return x

type Sheep = Int

father :: Sheep -> Maybe Sheep

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-- file: ch15/Supply.hs
next = S $ do st <- get
              case st of
              [] -> return Nothing
              (x:xs) -> do put xs
                           return (Just x)

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getD n = getD' n 2 where
         getD' n factor | n == factor = factor
                        | n `mod` factor == 0 = getD' (n `div` factor) factor
                        | otherwise = getD' n (succ factor)

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import Data.List

isUnique :: (Ord a) => [a] -> Bool
isUnique = all (null . drop 1) . group . sort

cols = [0..7]

solutions = [vec | vec <- permutations cols
                 , isUnique [vec!!i + i | i <- cols]
                 , isUnique [vec!!i - i | i <- cols]]

qzchenwl

import Data.List

isUnique :: (Ord a) => [a] -> Bool
isUnique = all (null . drop 1) . group . sort

cols = [0..7]
solutions = [vec | vec <- permutations cols
                 , isUnique [vec!!i + i | i <- cols]
                 , isUnique [vec!!i - i | i <- cols]]