EdX Introduction to Functional Programming in Haskell
Haskell uses lists instead of sets
[x^2 | x <-[1..5]]
x <-[1..5] called a generator as it defines how to generate values for x
can have multiple comma separated generators, which act like nested loops with later generators acting as the nested value.
>[(x, y) | x <-[1,2,3], y <- [4,5]]
[(1,4),(1,5),(2,4),(2,5),(3,4),(3,5)]
> [(x, y) | y <-[4,5], x <- [1,2,3]]
[(1,4),(2,4),(3,4),(1,5),(2,5),(3,5)]
2nd generator varies vaster as it acts as inner loop.
List comprehensions same idea as LINQ and SQL
later generators can refer to earlier generator variables just like an inner loop can reference variables in an outer loop
> [(x, y) | x <-[1..3], y <- [x..3]]
[(1,1),(1,2),(1,3),(2,2),(2,3),(3,3)]
-- flatten list
concat :: [[a]] -> [a]
concat xss = [x | xs <- xss, x <- xs]
[x | x <- [1..10], even x]
factors :: Int -> [Int]
factors n = [x | x <- [1..n], n `mod` x == 0]
prime :: Int -> Bool
prime n = factors n == [1,n]