From 6db87806aadc680edaa37a0143a60525629b660e Mon Sep 17 00:00:00 2001
From: Ben Sima <ben@bsima.me>
Date: Tue, 7 Aug 2018 10:57:08 -0700
Subject: WIP from last week

---
 rain/main.hs | 39 ++++++++++++++++++++++++++++-----------
 1 file changed, 28 insertions(+), 11 deletions(-)

diff --git a/rain/main.hs b/rain/main.hs
index 41ab03b..0133c2b 100755
--- a/rain/main.hs
+++ b/rain/main.hs
@@ -8,6 +8,7 @@
 -}
 
 {-# LANGUAGE TypeSynonymInstances #-}
+{-# LANGUAGE FlexibleInstances #-}
 
 {-
 
@@ -48,25 +49,41 @@ data Suit
   | Diamond
   | Heart
   | Spade
-  deriving (Show, Enum)
+  deriving (Show, Enum, Bounded)
 
 suits :: [Suit]
 suits = [ Club .. ]
 
-allCards :: [(Name, Suit)]
+type Card = (Name, Suit)
+
+instance Random Suit where
+    randomR (a, b) g =
+        case randomR (fromEnum a, fromEnum b) g of
+            (x, g') -> (toEnum x, g')
+    random g = randomR (minBound, maxBound) g
+
+instance Random Name where
+    randomR (a, b) g =
+        case randomR (fromEnum a, fromEnum b) g of
+            (x, g') -> (toEnum x, g')
+    random g = randomR (minBound, maxBound) g
+
+-- Dot product is same as 'liftA2 (,)'
+allCards :: [Card]
 allCards = liftA2 (,) names suits
 
-data CardsGen = CardsGen
-    deriving (Show)
+shuffle' :: [Card] -> _
+shuffle' (i:is) xs = (last firsts) : shuffle' is (init firsts ++ rest)
+    where (firsts, rest) = splitAt (i `mod` length xs) xs
 
---instance RandomGen CardsGen where
---    genRange _ = (0, cardsLength)
---    next CardsGen = stdNext (StdGen 0 cardsLength)
---    split = stdSplit (StdGen 0 cardsLength)
 
-suffle :: [cards] -> [cards]
-suffle arr = undefined
+shuffle g xs = shuffle (randoms g) xs
 
 main :: IO [()]
 main = do
-    sequence $ map (putStrLn.show) allCards
+    g <- getStdGen
+    let namesLength = length names
+    let randomNames = map fromEnum $ take namesLength $ randomRs (0, namesLength-1) g
+    let suitsLength = length suits
+    let randomSuits = map fromEnum $ take suitsLength $ randomRs (0, suitsLength-1) g
+    sequence $ map (putStrLn.show) $ liftA2 (,) randomNames randomSuits
-- 
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