scmu

{-

A program searching for solutions of a board puzzle
given by a friend.

The aim is to fill in a 8 by 8 square using the
given 8 pieces. Each piece has a particular shape and
can be rotated and flipped.

I am not satisfied with this program yet. The program

scmu

{-
   Richard Bird's quick algorithm for generating prime numbers.
   Note that the usual "one-liner" Haskell definition of the
   sieve is not an honest implementation of the sieve of Eratosthenes.
   The following algorithm by Bird is a more faithful implementation
   that is not asymptotically the best, but practically
   fast enough. Further more, we can reuse the "union" function.

   For more info see: Melissa E. O’Neill, The genuine sieve of

scmu

import Control.Arrow ((&&&))
import Data.String (unlines)
import Data.List (unfoldr,foldl')

histogram :: [Int] -> String
histogram = graph . histo

histo :: [Int] -> [Int]
histo = foldl' oplus [0,0,0,0,0,0,0,0,0,0]
  where oplus xs i = zipWith ($) (replicate i id ++ [(1+)] ++ repeat id) xs

scmu

import Data.Ord
import Data.List

nubSimple :: [Int] -> [Int]
nubSimple = map head . group . sort

nubStable :: [Int] -> [Int]
nubStable = map fst . sortBy (comparing snd). map head .
              groupBy ((. fst).(==).fst) . sort . flip zip [0..]