blob: 5af5b9b5dfa70b8c56403aacd793d0aa1648c0f3 (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
|
-- | Basic utilities
module PGF.Utilities where
import Data.Set(empty,member,insert)
-- | Like 'nub', but O(n log n) instead of O(n^2), since it uses a set to lookup previous things.
-- The result list is stable (the elements are returned in the order they occur), and lazy.
-- Requires that the list elements can be compared by Ord.
-- Code ruthlessly taken from http://hpaste.org/54411
nub' :: Ord a => [a] -> [a]
nub' = loop empty
where loop _ [] = []
loop seen (x : xs)
| member x seen = loop seen xs
| otherwise = x : loop (insert x seen) xs
-- | Replace all occurences of an element by another element.
replace :: Eq a => a -> a -> [a] -> [a]
replace x y = map (\z -> if z == x then y else z)
|
