1. Haskell
Chapter 1, Part II

2. List Comprehension
List comprehensions are a way to filter, transform and combine lists
Similar to mathematical set comprehensions
{2 * x | x e N, X <= 10}
In Haskell:
[x * 2 | x <- [1..10]]
“draw” our elements from the list [1..10]
so x takes on each value from 1 to 10
part before the pipe (|) is the output

3. With a predicate [x * 2 | x <- [50..100], x `mod` 7 == 3]
Using a predicate in this way is called filtering
Can separate predicates with a comma
[x | x <- [10..20], x /= 13, x /= 15, x /= 19]
Can draw from several lists
[x+y| x<-[1,2,3], y <- [10,100, 1000]]
result: [11,101,1001,12,102,1002,13,103,1003]

4. More list comprehensions
Can use a temporary variable
length' xs = sum [1 | _ <- xs]
Can be used with strings (they’re lists too)
removeNonUppercase st = [c | c <- st, c `elem` ['A'..'Z']]
Nested list comprehensions
-- let xxs = [[1,3,5,2,3,1,2,4,5],[1,2,3,4,5,6,7,8,9],[1,2,4,2,1,6,3,1,3,2,3,6]]
removeOdd xxs = [[x | x <- xs, even x] | xs <- xxs]
Function definitions – must load, not just interpret. Use let to bind.

5. Tuples Used to store several heterogeneous elements as a single value
Tuples have a fixed size
Elements surrounded by parentheses
(1,3)
(3, ‘a’, “hello”)
(50, 50.4, “hello”, ‘b’)
tuple of size 2 is a different type from tuple of size 3
tuples with different member elements are different types

6. More tuples Storing pairs is common in Haskell
Useful functions to manipulate:
fst
snd
zip [1,2,3] [4,5,6] => [(1,4),(2,5),(3,6)]
zip [1..] ["apple", "orange", "banana"] => [(1,"apple"),(2,"orange"),(3,"banana")]

7. Tuples in list comprehensions
Generate tuples
triples = [(a,b,c) | c <- [1..10], a<-[1..10], b<-[1..10]]
Generate tuples with filter
rightTriangle = [(a,b,c) | c <- [1..10], a<-[1..c], b<-[1..a],
a^2 + b^2 == c^2]

8. Play and Share evenOddPairs [1..4][20, 17, 23, 42]
evenCubes [1..20]
[8,64,216,512,1000,1728,2744,4096,5832,8000]
onlyBig [200,30,50,20,120] 100
[200,120]
noDiagonal [1..4]
[(1,2),(1,3),(1,4),(2,1),(2,3),(2,4),(3,1),(3,2),(3,4),(4,1),(4,2),(4,3)]
diagonal 10
[(0,0),(1,1),(2,2),(3,3),(4,4),(5,5),(6,6),(7,7),(8,8),(9,9),(10,10)]
countOdd [1..30] 15
evenOddPairs [1..4][20, 17, 23, 42]
[(2,17),(4,17),(2,23),(4,23)]
removeDigits "abc1d23A.98"
"abcdA.“
ends [[4,5,6],[1,2],[7,1,0]]
[6,2,0]
* These are parameters