Goals

The purpose of this worksheet is to practice using laziness, by creating some cyclic structures.

What to do

• Cut and paste the template below
• Fill in the undefined, so the structures have the
• To test your code properties described in the comments.

Your code will start something like:

module Lazy where
import Test.QuickCheck
import Data.Ratio

-- ones is an infinite list of ones. i.e. [1,1,1,1,...]
ones:: [Int]
ones = undefined

prop_ones n = all (==1) (take n ones)

-- from n is an infinite list of ascending numbers starting at n
from:: Int -> [Int]
from n = undefined

prop_from n m = ok (take n (from m))
  where ok [] = True
        ok [x] = True
        ok (x:y:zs) = (x+1)==y && ok (y:zs)

-- Another way to compute an infinite list of ascending unmbers
from2 = 2 : (map (+1) from2)

-- Define a property for quickcheck to test for from2
prop_from2 = undefined

-- Use the technique of from2 to create the list [1, 1/2, 1/4, 1/8, 1/16, ...]
-- You will need to use the operator (%) that builds ratios.  (1 % 4) --> 1/4
-- Two important ratios are:

one :: Ratio Integer
one = 1

half :: Ratio Integer
half = 1 % 2

converge :: [Ratio Integer]
converge = undefined

-- write test that shows the sum of the first n terms of
-- converge is always less than 2

prop_converge n = undefined

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