module CS254 where

import Char

--------------------
-- Some examples for early CS 254
-- Fritz Ruehr * Willamette * Spr 08


-- the Fibonacci numbers (as an infinite list)

fibs = 0 : 1 : zipWith (+) fibs (tail fibs)

infinity = 1 + infinity

n = n


-- the prime numbers (as an infinite list)

primes = sieve [2..]

sieve (n:ns) = n : sieve (filter ndiv ns)
               where ndiv k = k `mod` n /= 0


-- a quicksort program

qsort []     = []
qsort (x:xs) = qsort [ sm | sm <- xs, sm <  x ] ++ [x] ++
               qsort [ lg | lg <- xs, lg >= x ]

qs []     = []
qs (x:xs) = rec (<) ++ x : rec (>=)
            where rec p = qs (filter (`p` x) xs)


-- a program to test for palindromes

pal str = (new == reverse new)
          where new = norm str

norm = map toLower . filter isAlpha


-- some palindromes for testing

tests = [ "Madam, in Eden, I'm Adam." ,
          "A man, a plan, a canal ... Panama!" ,
          "" ,
          "A dog, a plan, a canal: pagoda." ,
          "Are we not drawn onward to new era?" ,
          "Cigar? Toss it in a can. It is so tragic." ,
          "Ed, I saw Harpo Marx ram Oprah W. aside." ,
          "No misses ordered roses, Simon." ,
          "A man, a plan, a cat, a ham, a yak, a yam, a hat, a canal - Panama!",
          "does it just work for everything?"

        ]

palword = "You can cage a swallow, can't you, but you can't swallow a cage, can you?"