104 lines
2.3 KiB
AppleScript
104 lines
2.3 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 :: [[a]] -> [a] | [String] -> String
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on concat(xs)
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script append
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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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if length of xs > 0 and class of (item 1 of xs) is string then
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set unit to ""
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else
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set unit to {}
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end if
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foldl(append, unit, 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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-- 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(xs)}
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--> {55, 3628800, "10987654321"}
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end run
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-- GENERIC FUNCTION -----------------------------------------------
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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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