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48 lines
1.2 KiB
Plaintext
48 lines
1.2 KiB
Plaintext
use Universal == <
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use Optional None Some
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uncons : [a] -> Optional (a, [a])
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uncons a = match at 0 a with
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None -> None
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Some hd -> Some (hd, drop 1 a)
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merge : (a -> a -> Boolean) -> [a] -> [a] -> [a]
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merge lte a b =
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go acc a b = match (uncons a, uncons b) with
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(None, _) -> acc ++ b
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(_, None) -> acc ++ a
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(Some (h1,t1), Some (h2,t2)) ->
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if lte h1 h2 then go (snoc acc h1) (drop 1 a) b
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else go (snoc acc h2) a (drop 1 b)
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go [] a b
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-- let's make sure it works
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> merge (<) [1,3,4,99,504,799] [0,19,22,23]
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isEmpty : [a] -> Boolean
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isEmpty a = size a == 0
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halve : [a] -> Optional ([a], [a])
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halve as =
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if isEmpty as then None
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else Some (take (size as / 2) as, drop (size as / 2) as)
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sort : (a -> a -> Boolean) -> [a] -> [a]
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sort lte as = if size as < 2 then as else match halve as with
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None -> as
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Some (left, right) ->
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l = sort lte left
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r = sort lte right
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merge lte l r
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-- let's make sure it works
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> sort (<) [3,2,1,1,2,3,9182,1,2,34,1,23]
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-- > sort (<) ["Dave", "Carol", "Eve", "Alice", "Bob", "Francis", "Hal", "Illy", "Joanna", "Greg", "Karen"]
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-- > sort (<) [3,2,1,1,2,3,9182,1,2,34,1,"oops"]
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-- > merge (<) [1,4,5,90,102] ["a", "b"]
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