39 lines
919 B
Haskell
39 lines
919 B
Haskell
extract :: [a] -> a
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extract [] = error("Too few objects")
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extract (x:xs) = x
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a = extract [1,2,3,4,5]
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-- a == 1
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-- better use fst
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addto :: (Num a) => [a] -> a -> [a]
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addto [] _ = [] -- edge case (list empty)
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addto (x:xs) y = (x+y) : addto xs y
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b = [1..4]
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c = addto b 4
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-- c == [5,6,7,8]
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-- better use c = map (+4) b
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-- d == [25,36,49,64]
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d = map (^2) c
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e = filter (\x -> (mod x 2) == 0) c
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-- e == [6,8]
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mfold :: (t -> t1 -> t1) -> t1 -> [t] -> t1
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mfold f z [] = z
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mfold f z (x:xs) = f x (mfold f z xs)
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msum = mfold (+) 0
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g = msum [1..100]
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-- use sum [1..100] instead, and use right folds
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pt = [(a,b,c) | a <- [1..15], b <- [1..a], c <- [1..b], a^2 == b^2 + c^2]
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bsort :: (t -> t -> Bool) -> [t] -> [t]
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bsort f [] = []
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bsort f (x:xs) = (bsort f a) ++ [x] ++ (bsort f b)
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where a = [ y | y <- xs, not (f x y) ]
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b = [ y | y <- xs, (f x y) ]
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mbsort = bsort (\x y -> (x < y))
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h = [1, 20, -10, 5]
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i = mbsort h
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