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<!doctype html><title>CodeMirror: Haskell mode</title><meta charset="utf-8" /><link rel=stylesheet href="../../doc/docs.css"><link rel="stylesheet" href="../../lib/codemirror.css"><link rel="stylesheet" href="../../theme/elegant.css"><script src="../../lib/codemirror.js"></script><script src="../../addon/edit/matchbrackets.js"></script><script src="haskell.js"></script><style type="text/css">.CodeMirror {border-top: 1px solid black;border-bottom: 1px solid black;}</style><div id=nav><a href="http://codemirror.net"><h1>CodeMirror</h1><img id=logo src="../../doc/logo.png"></a><ul><li><a href="../../index.html">Home</a><li><a href="../../doc/manual.html">Manual</a><li><a href="https://github.com/codemirror/codemirror">Code</a></ul><ul><li><a href="../index.html">Language modes</a><li><a class=active href="#">Haskell</a></ul></div><article><h2>Haskell mode</h2><form><textarea id="code" name="code"> module UniquePerms ( uniquePerms ) where -- | Find all unique permutations of a list where there might be duplicates. uniquePerms :: (Eq a) => [a] -> [[a]] uniquePerms = permBag . makeBag -- | An unordered collection where duplicate values areallowed, -- but represented with a single value and a count. type Bag a = [(a, Int)] makeBag :: (Eq a) => [a] -> Bag a makeBag [] = [] makeBag (a:as) = mix a $ makeBag as where mix a [] = [(a,1)] mix a (bn@(b,n):bs) | a == b = (b,n+1):bs |otherwise = bn : mix a bs permBag :: Bag a -> [[a]] permBag [] = [[]] permBag bs = concatMap (\(f,cs) -> map (f:) $ permBag cs) . oneOfEach $ bs where oneOfEach [] = [] oneOfEach (an@(a,n):bs) = let bs' = if n == 1 then bs else (a,n-1):bsin (a,bs') : mapSnd (an:) (oneOfEach bs) apSnd f (a,b) = (a, f b) mapSnd = map . apSnd </textarea></form><script>var editor = CodeMirror.fromTextArea(document.getElementById("code"),{lineNumbers: true,matchBrackets: true,theme: "elegant"});</script><p><strong>MIME types defined:</strong> <code>text/x-haskell</code>.</p></article>