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1 <!doctype html>
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2
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3 <title>CodeMirror: Haskell mode</title>
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4 <meta charset="utf-8"/>
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5 <link rel=stylesheet href="../../doc/docs.css">
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6
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7 <link rel="stylesheet" href="../../lib/codemirror.css">
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9 <script src="../../lib/codemirror.js"></script>
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11 <script src="haskell.js"></script>
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12 <style>.CodeMirror {border-top: 1px solid black; border-bottom: 1px solid black;}</style>
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13 <div id=nav>
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14 <a href="https://codemirror.net/5"><h1>CodeMirror</h1><img id=logo src="../../doc/logo.png" alt=""></a>
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15
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16 <ul>
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17 <li><a href="../../index.html">Home</a>
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20 </ul>
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21 <ul>
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22 <li><a href="../index.html">Language modes</a>
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23 <li><a class=active href="#">Haskell</a>
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24 </ul>
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25 </div>
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26
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27 <article>
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28 <h2>Haskell mode</h2>
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29 <form><textarea id="code" name="code">
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30 module UniquePerms (
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31 uniquePerms
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32 )
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33 where
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34
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35 -- | Find all unique permutations of a list where there might be duplicates.
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36 uniquePerms :: (Eq a) => [a] -> [[a]]
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37 uniquePerms = permBag . makeBag
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38
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39 -- | An unordered collection where duplicate values are allowed,
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40 -- but represented with a single value and a count.
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41 type Bag a = [(a, Int)]
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42
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43 makeBag :: (Eq a) => [a] -> Bag a
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44 makeBag [] = []
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45 makeBag (a:as) = mix a $ makeBag as
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46 where
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47 mix a [] = [(a,1)]
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48 mix a (bn@(b,n):bs) | a == b = (b,n+1):bs
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49 | otherwise = bn : mix a bs
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50
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51 permBag :: Bag a -> [[a]]
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52 permBag [] = [[]]
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53 permBag bs = concatMap (\(f,cs) -> map (f:) $ permBag cs) . oneOfEach $ bs
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54 where
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55 oneOfEach [] = []
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56 oneOfEach (an@(a,n):bs) =
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57 let bs' = if n == 1 then bs else (a,n-1):bs
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58 in (a,bs') : mapSnd (an:) (oneOfEach bs)
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59
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60 apSnd f (a,b) = (a, f b)
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61 mapSnd = map . apSnd
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62 </textarea></form>
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63
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64 <script>
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65 var editor = CodeMirror.fromTextArea(document.getElementById("code"), {
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66 lineNumbers: true,
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67 matchBrackets: true,
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68 theme: "elegant"
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69 });
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70 </script>
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71
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72 <p><strong>MIME types defined:</strong> <code>text/x-haskell</code>.</p>
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73 </article>
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