From 6a106374d560e9a0b24c54858d5f601b38434f4e Mon Sep 17 00:00:00 2001
From: Mysaa <samy.avrillon@ens-lyon.fr>
Date: Mon, 3 Jan 2022 12:06:30 +0100
Subject: [PATCH] Fiche Haskell 13

---
 HSK13.md   | 85 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 fstfunc.hs | 63 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 148 insertions(+)
 create mode 100644 HSK13.md

diff --git a/HSK13.md b/HSK13.md
new file mode 100644
index 0000000..6d3e914
--- /dev/null
+++ b/HSK13.md
@@ -0,0 +1,85 @@
+# Haskell 13
+
+### Exercice 1
+1. Le pattern matching est un moyen d'extraire des variables d'une variable *composite* comme une liste, un tuple par exemple. Cela permet aussi de vérifier qu'une variable a bien une forme donnée, ou de faire une disjonction de cas.
+2. Cela permet d'écrire des fonctions très proches de la notation mathématiques et très simple à écrire et surtout à comprendre ca très visuelles.
+3. 
+```
+greaterTwo :: [Char] -> Bool
+greaterTwo "one" = False
+greaterTwo "two" = False
+greaterTwo _ = True
+```
+4. Les motifs sont lus dans l'ordre dans lequel ils ont été écrits. C'est à dire que les premiers motifs prévalent.
+5. 
+```
+divide :: Fractional a => Eq a => a -> a -> a
+divide _ 0 = -9999
+divide p q = p/q
+```
+
+### Exercice 2
+```
+myand :: Bool -> Bool -> Bool
+myand False False = False
+myand True False = True
+myand False True = True
+myand True True = False
+
+myand2 :: Bool -> Bool -> Bool
+myand2 False b = b
+myand2 True b = not b
+```
+
+### Exercice 3
+```
+compVectOld :: (Double,Double) -> (Double,Double) -> Double
+compVectOld u v = ((fst u) + (fst v)) * ((snd u) + (snd v))
+
+compVect :: Real a => (a,a) -> (a,a) -> a
+compVect (x,y) (w,z) = (x+y)*(w+z)
+```
+
+L'intéret du *pattern matching* est de rendre la lecture et la compréhension du code beaucoup plus simple.
+
+### Exercice 4
+Voir fstfunc.hs
+
+### Exercice 5
+Voir fstfunc.hs
+
+### Exercice 6
+1. OK
+2. Pour ajouter un élément en tête de liste, il suffit d'utiliser l'opérateur *cons* dénoté par `:`.
+3. Le premier pattern correspond uniquement à la liste vide. Le second correspond à toute liste avec pour dernier constructeur *cons*. Ce qui veut dire qu'il correspond à toute liste non vide (il n'y a que deux constructeurs). La variable de tête est assignée au nom `x` et le reste est ignoré.
+4. Correspondent toutes les listes non vides.
+
+### Exercice 7
+1. 
+```
+twoEq :: Eq a => [a] -> [a] -> Bool
+twoEq (x:_) (y:_) = (x==y)
+twoEq [] [] = True
+twoEq _ _ = False
+```
+2. Les éléments doivent être de la classe `Eq` afin de pouvoir être comparés.
+
+### Exercice 8
+1. 
+```
+myLength :: PrintfType r => [a] -> r
+myLength [] = printf "The list has no elements\n"
+myLength [x] = printf "The list has one element\n"
+myLength [x,y] = printf "The list has two elements\n"
+myLength _ = printf "The list has more than two elements\n"
+```
+2. Les objets doivent étendrent la classe `Show` pour être affichés.
+
+3. 
+```
+myLengthShow :: PrintfType r => Show a => [a] -> r
+myLengthShow [] = printf "The list has no elements\n"
+myLengthShow [x] = printf "The list has one element: %s\n" (show x)
+myLengthShow [x,y] = printf "The list has two elements: %s and %s\n" (show x) (show y)
+myLengthShow _ = printf "The list has more than two elements\n"
+```
diff --git a/fstfunc.hs b/fstfunc.hs
index 60e519c..7efbb39 100644
--- a/fstfunc.hs
+++ b/fstfunc.hs
@@ -1,4 +1,6 @@
 {-# LANGUAGE ParallelListComp #-}
+import Text.Printf
+
 addTwo :: Num a => a -> a
 addTwo x = x + 2
 
@@ -17,3 +19,64 @@ addList xs ys = [x+y | x <- xs, y <- ys]
 
 length2 :: [a] -> Int
 length2 xs = last [n | _ <- xs | n <- [2,4..]]
+
+greaterTwo :: [Char] -> Bool
+greaterTwo "one" = False
+greaterTwo "two" = False
+greaterTwo _ = True
+
+divide :: Fractional a => Eq a => a -> a -> a
+divide _ 0 = -9999
+divide p q = p/q
+
+myand :: Bool -> Bool -> Bool
+myand False False = False
+myand True False = True
+myand False True = True
+myand True True = False
+
+myand2 :: Bool -> Bool -> Bool
+myand2 False b = b
+myand2 True b = not b
+
+compVectOld :: (Double,Double) -> (Double,Double) -> Double
+compVectOld u v = ((fst u) + (fst v)) * ((snd u) + (snd v))
+
+compVect :: Real a => (a,a) -> (a,a) -> a
+compVect (x,y) (w,z) = (x+y)*(w+z)
+
+myFst :: (a,a,a) -> a
+myFst (x,y,z) = x
+
+mySnd :: (a,a,a) -> a
+mySnd (x,y,z) = y
+
+myThd :: (a,a,a) -> a
+myThd (x,y,z) = z
+
+listPat :: Num a => [(a,a,a)] -> [a]
+listPat [] = []
+listPat ((x,y,z):s) = (x+y*z):(listPat s)
+
+myHead :: [a] -> a
+myHead [] = error "The list is empty !"
+myHead (x:_) = x
+
+twoEq :: Eq a => [a] -> [a] -> Bool
+twoEq (x:_) (y:_) = (x==y)
+twoEq [] [] = True
+twoEq _ _ = False
+
+myLength :: PrintfType r => [a] -> r
+myLength [] = printf "The list has no elements\n"
+myLength [x] = printf "The list has one element\n"
+myLength [x,y] = printf "The list has two elements\n"
+myLength _ = printf "The list has more than two elements\n"
+
+myLengthShow :: PrintfType r => Show a => [a] -> r
+myLengthShow [] = printf "The list has no elements\n"
+myLengthShow [x] = printf "The list has one element: %s\n" (show x)
+myLengthShow [x,y] = printf "The list has two elements: %s and %s\n" (show x) (show y)
+myLengthShow _ = printf "The list has more than two elements\n"
+
+