122 lines
2.5 KiB
AppleScript
122 lines
2.5 KiB
AppleScript
---------------------- CATAMORPHISMS ---------------------
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-- the arguments available to the called function f(a, x, i, l) are
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-- a: current accumulator value
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-- x: current item in list
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-- i: [ 1-based index in list ] optional
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-- l: [ a reference to the list itself ] optional
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-- foldl :: (a -> b -> a) -> a -> [b] -> a
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on foldl(f, startValue, xs)
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tell mReturn(f)
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set v to startValue
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set lng to length of xs
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repeat with i from 1 to lng
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set v to |λ|(v, item i of xs, i, xs)
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end repeat
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return v
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end tell
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end foldl
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-- the arguments available to the called function f(a, x, i, l) are
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-- a: current accumulator value
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-- x: current item in list
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-- i: [ 1-based index in list ] optional
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-- l: [ a reference to the list itself ] optional
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-- foldr :: (a -> b -> a) -> a -> [b] -> a
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on foldr(f, startValue, xs)
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tell mReturn(f)
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set v to startValue
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set lng to length of xs
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repeat with i from lng to 1 by -1
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set v to |λ|(v, item i of xs, i, xs)
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end repeat
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return v
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end tell
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end foldr
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--- OTHER FUNCTIONS DEFINED IN TERMS OF FOLDL AND FOLDR --
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-- concat :: [String] -> string
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on concat(xs)
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foldl(my append, "", xs)
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end concat
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-- product :: Num a => [a] -> a
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on product(xs)
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script
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on |λ|(a, b)
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a * b
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end |λ|
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end script
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foldr(result, 1, xs)
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end product
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-- str :: a -> String
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on str(x)
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x as string
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end str
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-- sum :: Num a => [a] -> a
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on sum(xs)
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script
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on |λ|(a, b)
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a + b
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end |λ|
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end script
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foldl(result, 0, xs)
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end sum
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--------------------------- TEST -------------------------
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on run
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set xs to {1, 2, 3, 4, 5, 6, 7, 8, 9, 10}
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{sum(xs), product(xs), concat(map(str, xs))}
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--> {55, 3628800, "10987654321"}
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end run
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-------------------- GENERIC FUNCTIONS -------------------
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-- append :: String -> String -> String
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on append(a, b)
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a & b
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end append
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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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-- Lift 2nd class handler function into 1st class script wrapper
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-- mReturn :: Handler -> Script
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on mReturn(f)
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if class of f is script 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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