From a32f460a998b2d4b24ac619292c9c5f599e28c7d Mon Sep 17 00:00:00 2001
From: Tristan Cacqueray <tdecacqu@redhat.com>
Date: May 09 2019 11:42:32 +0000
Subject: Add tdecacqu answers for the first week


Depends-On: https://pagure.io/cis194/pull-request/1

---

diff --git a/assignments/tdecacqu/01.lhs b/assignments/tdecacqu/01.lhs
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+Syntax note:
+
+* otherwise == True
+* 5 `mod` 2  == mod 5 2
+
+Useful function
+
+* fromIntegral: convert Int to other numeric types
+* round, floor, ceiling: convert numeric types to Int
+
+Enable unicode symbols:
+
+> {-# LANGUAGE UnicodeSyntax #-}
+> -- https://stackoverflow.com/questions/24441661/haskell-mode-not-working-for-my-project-cant-find-module
+> import Prelude.Unicode
+
+Add a main
+
+> main :: IO ()
+> main = print "Hello"
+
+** Exercise 1
+
+First the toDigitsRev as it's more natural with cons:
+
+> toDigitsRev ∷ Integer → [Integer]
+> toDigitsRev x
+>   | x ≤ 0      = []
+>   | x ≥ 10     = mod x 10 : toDigitsRev (div x 10)
+>   | otherwise  = [x]
+
+Then a procedure to reverse a list:
+
+> listRev ∷ [a] → [a]
+> listRev (x:xs) = listRev xs ++ [x]
+> listRev []     = []
+
+
+> toDigits ∷ Integer → [Integer]
+> toDigits x = listRev (toDigitsRev x)
+
+** Exercise 2
+
+The exercise requires the list to be processed from right to left.
+This implementation uses a Do function that works on the reversed list
+
+> doubleEveryOtherDo ∷ [Integer] → [Integer]
+> doubleEveryOtherDo (x:y:xs) = x : y ⋅ 2 : doubleEveryOtherDo xs
+> doubleEveryOtherDo (x:[]) = [x]
+> doubleEveryOtherDo [] = []
+
+> doubleEveryOther ∷ [Integer] -> [Integer]
+> doubleEveryOther x = reverse (doubleEveryOtherDo (reverse x))
+
+** Exercise 3
+
+> sumDigits ∷ [Integer] → Integer
+> sumDigits (x:xs) = sum (toDigits x) + sumDigits xs
+> sumDigits [] = 0
+
+** Exercise 4
+
+> validate ∷ Integer → Bool
+> validate x = rem (sumDigits (doubleEveryOther (toDigits x))) 10 ≡ 0
+
+** Exercise 5
+
+> type Peg = String
+> type Move = (Peg, Peg)
+> hanoi ∷ Integer → Peg → Peg -> Peg → [Move]
+> hanoi count source dest spare
+>  | count ≡ 0 = []
+>  | otherwise = hanoi (count - 1) source spare dest ++
+>                [(source, dest)] ++
+>                hanoi (count - 1) spare dest source
+
+** Exercise 6
+
+-- TODO