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Task/Amicable-pairs/AppleScript/amicable-pairs-1.applescript

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+-- AMICABLE PAIRS ------------------------------------------------------------
+
+-- amicablePairsUpTo :: Int -> Int
+on amicablePairsUpTo(max)
+
+    -- amicable :: [Int] -> Int -> Int -> [Int] -> [Int]
+    script amicable
+        on |λ|(a, m, n, lstSums)
+            if (m > n) and (m ≤ max) and ((item m of lstSums) = n) then
+                a & [[n, m]]
+            else
+                a
+            end if
+        end |λ|
+    end script
+
+    -- divisorsSummed :: Int -> Int
+    script divisorsSummed
+        -- sum :: Int -> Int -> Int
+        script sum
+            on |λ|(a, b)
+                a + b
+            end |λ|
+        end script
+
+        on |λ|(n)
+            foldl(sum, 0, properDivisors(n))
+        end |λ|
+    end script
+
+    foldl(amicable, {}, ¬
+        map(divisorsSummed, enumFromTo(1, max)))
+end amicablePairsUpTo
+
+
+-- TEST ----------------------------------------------------------------------
+on run
+
+    amicablePairsUpTo(20000)
+
+end run
+
+
+-- PROPER DIVISORS -----------------------------------------------------------
+
+-- properDivisors :: Int -> [Int]
+on properDivisors(n)
+
+    -- isFactor :: Int -> Bool
+    script isFactor
+        on |λ|(x)
+            n mod x = 0
+        end |λ|
+    end script
+
+    -- integerQuotient :: Int -> Int
+    script integerQuotient
+        on |λ|(x)
+            (n / x) as integer
+        end |λ|
+    end script
+
+    if n = 1 then
+        {1}
+    else
+        set realRoot to n ^ (1 / 2)
+        set intRoot to realRoot as integer
+        set blnPerfectSquare to intRoot = realRoot
+
+        -- Factors up to square root of n,
+        set lows to filter(isFactor, enumFromTo(1, intRoot))
+
+        -- and quotients of these factors beyond the square root,
+        -- excluding n itself (last item)
+        items 1 thru -2 of (lows & map(integerQuotient, ¬
+            items (1 + (blnPerfectSquare as integer)) thru -1 of reverse of lows))
+    end if
+end properDivisors
+
+-- GENERIC FUNCTIONS ---------------------------------------------------------
+
+-- enumFromTo :: Int -> Int -> [Int]
+on enumFromTo(m, n)
+    if m > n then
+        set d to -1
+    else
+        set d to 1
+    end if
+    set lst to {}
+    repeat with i from m to n by d
+        set end of lst to i
+    end repeat
+    return lst
+end enumFromTo
+
+-- filter :: (a -> Bool) -> [a] -> [a]
+on filter(f, xs)
+    tell mReturn(f)
+        set lst to {}
+        set lng to length of xs
+        repeat with i from 1 to lng
+            set v to item i of xs
+            if |λ|(v, i, xs) then set end of lst to v
+        end repeat
+        return lst
+    end tell
+end filter
+
+-- foldl :: (a -> b -> a) -> a -> [b] -> a
+on foldl(f, startValue, xs)
+    tell mReturn(f)
+        set v to startValue
+        set lng to length of xs
+        repeat with i from 1 to lng
+            set v to |λ|(v, item i of xs, i, xs)
+        end repeat
+        return v
+    end tell
+end foldl
+
+-- map :: (a -> b) -> [a] -> [b]
+on map(f, xs)
+    tell mReturn(f)
+        set lng to length of xs
+        set lst to {}
+        repeat with i from 1 to lng
+            set end of lst to |λ|(item i of xs, i, xs)
+        end repeat
+        return lst
+    end tell
+end map
+
+-- Lift 2nd class handler function into 1st class script wrapper
+-- mReturn :: Handler -> Script
+on mReturn(f)
+    if class of f is script then
+        f
+    else
+        script
+            property |λ| : f
+        end script
+    end if
+end mReturn