| 1 | <!doctype html> |
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| 2 | <html> |
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| 3 | <head> |
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| 4 | <title>CodeMirror 2: Haskell mode</title> |
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| 5 | <link rel="stylesheet" href="../../lib/codemirror.css"> |
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| 6 | <script src="../../lib/codemirror.js"></script> |
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| 7 | <script src="haskell.js"></script> |
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| 8 | <link rel="stylesheet" href="haskell.css"> |
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| 9 | <style type="text/css">.CodeMirror {border-top: 1px solid black; border-bottom: 1px solid black;}</style> |
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| 10 | <link rel="stylesheet" href="../../css/docs.css"> |
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| 11 | </head> |
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| 12 | <body> |
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| 13 | <h1>CodeMirror 2: Haskell mode</h1> |
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| 14 | |
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| 15 | <form><textarea id="code" name="code"> |
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| 16 | module UniquePerms ( |
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| 17 | uniquePerms |
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| 18 | ) |
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| 19 | where |
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| 20 | |
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| 21 | -- | Find all unique permutations of a list where there might be duplicates. |
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| 22 | uniquePerms :: (Eq a) => [a] -> [[a]] |
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| 23 | uniquePerms = permBag . makeBag |
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| 24 | |
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| 25 | -- | An unordered collection where duplicate values are allowed, |
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| 26 | -- but represented with a single value and a count. |
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| 27 | type Bag a = [(a, Int)] |
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| 28 | |
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| 29 | makeBag :: (Eq a) => [a] -> Bag a |
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| 30 | makeBag [] = [] |
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| 31 | makeBag (a:as) = mix a $ makeBag as |
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| 32 | where |
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| 33 | mix a [] = [(a,1)] |
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| 34 | mix a (bn@(b,n):bs) | a == b = (b,n+1):bs |
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| 35 | | otherwise = bn : mix a bs |
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| 36 | |
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| 37 | permBag :: Bag a -> [[a]] |
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| 38 | permBag [] = [[]] |
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| 39 | permBag bs = concatMap (\(f,cs) -> map (f:) $ permBag cs) . oneOfEach $ bs |
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| 40 | where |
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| 41 | oneOfEach [] = [] |
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| 42 | oneOfEach (an@(a,n):bs) = |
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| 43 | let bs' = if n == 1 then bs else (a,n-1):bs |
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| 44 | in (a,bs') : mapSnd (an:) (oneOfEach bs) |
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| 45 | |
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| 46 | apSnd f (a,b) = (a, f b) |
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| 47 | mapSnd = map . apSnd |
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| 48 | </textarea></form> |
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| 49 | |
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| 50 | <script> |
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| 51 | var editor = CodeMirror.fromTextArea(document.getElementById("code"), { |
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| 52 | lineNumbers: true, |
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| 53 | matchBrackets: true |
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| 54 | }); |
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| 55 | </script> |
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| 56 | |
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| 57 | <p><strong>MIME types defined:</strong> <code>text/x-haskell</code>.</p> |
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| 58 | </body> |
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| 59 | </html> |
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