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47 lines
1.1 KiB
Plaintext
47 lines
1.1 KiB
Plaintext
use Optional None Some
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use Universal <
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uncons : [a] -> Optional (a, [a])
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uncons as = match at 0 as with
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None -> None
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Some hd -> Some (hd, drop 1 as)
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halve : [a] -> ([a], [a])
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halve s = splitAt (size s / 2) s
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splitAt : Nat -> [a] -> ([a], [a])
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splitAt n as = (take n as, drop n as)
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merge : (a -> a -> Boolean) -> [a] -> [a] -> [a]
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merge lte a b =
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use List ++
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go out a b = match (uncons a, uncons b) with
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(None,_) -> out ++ b
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(_,None) -> out ++ a
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(Some (hA, tA), Some (hB, tB)) ->
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if hA `lte` hB then go (out `snoc` hA) tA b
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else go (out `snoc` hB) a tB
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go [] a b
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sort : (a -> a -> Boolean) -> [a] -> [a]
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sort lte as =
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if size as < 2 then as
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else match halve as with (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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> uncons [1, 2, 3]
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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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-- these programs have some type errors
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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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