1. Haskell Examples
10-May-19

2. Factorial fact n = if n == 0 then 1 else n * fact (n - 1) fac 0 = 1
fac (n+1) = (n+1)*fac n

3. Quadratic Formula quadsolve a b c
| delta < 0 = error "complex roots"
| delta == 0 = [-b/(2*a)]
| delta > 0 = [-b/(2*a) + radix/(2*a),
-b/(2*a) - radix/(2*a)]
where
delta = b*b - 4*a*c
radix = sqrt delta
Main> quadsolve 1 4 (-12)
[2.0,-6.0]

4. Permutations perms :: [a] -> [[a]] perms [] = [[]] perms (h:t) =
[take n x ++ [h] ++ drop n x
| n <- [0..length t], x <- perms t]
Main> perms "abc"
["abc","acb","bac","cab","bca","cba"]

5. a p p l e -> a p p l e h a y s t r i p e -> i p e s t r a y
Pig Latin
Pig Latin is a child’s “secret language”
Rearranges sounds in words depending on whether word begins with a vowel sound
a p p l e -> a p p l e h a y
s t r i p e -> i p e s t r a y

6. Pig Latin for single words
latinizeWord w = back w ++ front w ++ suffix w
where front w = fst (breakWord w)
back w = snd (breakWord w)
suffix w = if front w == "" then "hay"
else "ay"
breakWord w = span (`notElem` "aeiou") w
Main> latinizeWord "stripe"
"ipestray"

7. Pig Latin for sentences I
Main> words "Haskell is fun"
["Haskell","is","fun"]
Main> unwords (words "Haskell is fun")
"Haskell is fun"
Main> unwords (words "Haskell is fun")
"Haskell is fun"

8. Pig Latin for sentences II
latinize s = unwords (map latinizeWord (words s))
Main> latinize "Haskell is fun"
"askellHay ishay unfay"

9. unwords unwords :: [String] -> String unwords [] = ""
words and unwords are already defined in the Standard Prelude
unwords :: [String] -> String
unwords [] = ""
unwords ws = foldr1 (\w s -> w ++ ' ':s) ws

10. unwords (again) unwds :: [[Char]] -> [Char] unwds [] = []
unwds (h:t) = h ++ " " ++ unwds t

11. Fibonacci Numbers Main> zip ['a'..'z'] [1..5]
[('a',1),('b',2),('c',3),('d',4),('e',5)]
fib = 1:1:[a+b | (a, b) <- zip fib (tail fib)]
Main> take 10 fib
[1,1,2,3,5,8,13,21,34,55]

12. The End