haskell-syntax-bonus-exercises-questions.md

Haskell Syntax Bonus Exercises

Questions

Expression forms

Identify the form (normal form, weak head normal form, or redex) of each of the following expressions:

1. 23
2. (2,3)
3. \x -> 2 + 3
4. (\x -> x + 2) 3
5. (\x -> \y -> x + y) 2
6. 2 + 3
7. (2 + 2, 3 + 3)
8. Just (2 + 3)
9. Just 5
10. [1,2,3] ++ [4,5,6]
11. Just $ [1,2,3] ++ [4,5,6]
12. [Just 1, Just 2, Just (2 + 3)]
13. [Just (1,2), Just (2,3), Just (4,5)]
14. \x -> \y -> \z -> x + y(z)
15. \x -> ((\y -> y + 1) 1) + x
16. [[1,2,3]]
17. [1,2,3] : []
18. [1 + 1]
19. [1] ++ []
20. (+) 1
21. (+) 1 2
22. print
23. div (1 + 2 * 3 - 4)
24. (+ 2)
25. (- 3)

Application operator

Replace the parentheses with the $ operator in the following expressions:

1. take 1 (drop 1 [1..10])
2. fst (swap (swap (2,3)))
3. unwords (words (str ++ "!"))
4. intersect (nub (union [1,2,2,3,4,5,5,5,6,6,7] [2,4,6,8])) [2,4,6,8]
5. map snd (zip (zipWith ($) [(+3),(+2),(+1)] [1,2,3]) "abc")

let vs. where

Rewrite the following let expressions to use where instead.

1. whiteLines colors = let w = "white" in intersperse w colors
2. abs n = let n' = negate n in if n < 0 then n' else n
3. f x y z = let a = x * (y - z) in a <= 0