110 lines
2.5 KiB
AppleScript
110 lines
2.5 KiB
AppleScript
----------------------- QUICKSELECT ------------------------
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-- quickSelect :: Ord a => [a] -> Int -> a
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on quickSelect(xxs)
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script
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on |λ|(k)
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script go
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on |λ|(xxs, k)
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set {x, xs} to {item 1 of xxs, rest of xxs}
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set {ys, zs} to partition(gt(x), xs)
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set lng to length of ys
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if k < lng then
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|λ|(ys, k)
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else
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if k > lng then
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|λ|(zs, k - lng - 1)
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else
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x
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end if
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end if
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end |λ|
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end script
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if 0 ≤ k and k < length of xxs then
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tell go to |λ|(xxs, k)
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else
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missing value
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end if
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end |λ|
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end script
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end quickSelect
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--------------------------- TEST ---------------------------
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on run
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set xs to {9, 8, 7, 6, 5, 0, 1, 2, 3, 4}
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map(quickSelect(xs), enumFromTo(0, (length of xs) - 1))
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end run
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----------- GENERAL AND REUSABLE PURE FUNCTIONS ------------
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-- enumFromTo :: Int -> Int -> [Int]
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on enumFromTo(m, n)
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if m ≤ n then
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set lst to {}
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repeat with i from m to n
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set end of lst to i
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end repeat
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lst
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else
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{}
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end if
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end enumFromTo
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-- gt :: Ord a => a -> a -> Bool
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on gt(x)
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script
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on |λ|(y)
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x > y
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end |λ|
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end script
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end gt
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-- map :: (a -> b) -> [a] -> [b]
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on map(f, xs)
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-- The list obtained by applying f
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-- to each element of xs.
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tell mReturn(f)
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set lng to length of xs
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set lst to {}
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repeat with i from 1 to lng
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set end of lst to |λ|(item i of xs, i, xs)
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end repeat
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return lst
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end tell
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end map
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-- mReturn :: First-class m => (a -> b) -> m (a -> b)
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on mReturn(f)
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-- 2nd class handler function lifted into 1st class script wrapper.
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if script is class of f then
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f
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else
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script
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property |λ| : f
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end script
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end if
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end mReturn
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-- partition :: (a -> Bool) -> [a] -> ([a], [a])
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on partition(p, xs)
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tell mReturn(p)
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set {ys, zs} to {{}, {}}
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repeat with x in xs
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set v to contents of x
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if |λ|(v) then
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set end of ys to v
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else
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set end of zs to v
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end if
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end repeat
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end tell
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{ys, zs}
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end partition
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