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1 module AllEven where
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2 allEven :: [Integer] -> [Integer]
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3 allEven [] = []
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4 -- Note: "h:allEven t" doesn't parse the same as some other languages. We're not invoking anything on "h".
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5 -- It is literally "h" joined to the list made by "allEven t"
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6 allEven (h:t) = if even h then h:allEven t else allEven t
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7
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8 allEvenGuard :: [Integer] -> [Integer]
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9 allEvenGuard [] = []
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10 -- We can't include the empty list case because decomposing an empty list with "h:t" gives the exception "Non-exhaustive patterns in h : t"
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11 allEvenGuard (h:t)
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12 | even h = h:allEven t
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13 | otherwise = allEven t
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14
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15 allEvenComp :: [Integer] -> [Integer]
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16 allEvenComp lst = [x | x <- lst, even x] |
