2016 Update

Task/Apply-a-callback-to-an-array/AppleScript/apply-a-callback-to-an-array-1.applescript

@@ -0,0 +1,11 @@
+on callback for arg
+    -- Returns a string like "arc has 3 letters"
+    arg & " has " & (count arg) & " letters"
+end callback
+
+set alist to {"arc", "be", "circle"}
+repeat with aref in alist
+    -- Passes a reference to some item in alist
+    -- to callback, then speaks the return value.
+    say (callback for aref)
+end repeat

Task/Apply-a-callback-to-an-array/AppleScript/apply-a-callback-to-an-array-2.applescript

@@ -0,0 +1,78 @@
+on run
+
+    set xs to {1, 2, 3, 4, 5, 6, 7, 8, 9, 10}
+
+    {map(square, xs), ¬
+        filter(isEven, xs), ¬
+        foldl(sum, 0, xs)}
+
+    --> {{1, 4, 9, 16, 25, 36, 49, 64, 81, 100}, {2, 4, 6, 8, 10}, 55}
+
+end run
+
+-- square :: Num -> Num -> Num
+on square(x)
+    x * x
+end square
+
+-- sum :: Num -> Num -> Num
+on sum(a, b)
+    a + b
+end sum
+
+-- isEven :: Int -> Bool
+on isEven(n)
+    n mod 2 = 0
+end isEven
+
+
+-- GENERIC HIGHER ORDER FUNCTIONS
+
+-- 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 lambda(item i of xs, i, xs)
+        end repeat
+        return lst
+    end tell
+end map
+
+-- 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 lambda(v, item i of xs, i, xs)
+        end repeat
+        return v
+    end tell
+end foldl
+
+-- 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 lambda(v, i, xs) then set end of lst to v
+        end repeat
+        return lst
+    end tell
+end filter
+
+-- 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 lambda : f
+        end script
+    end if
+end mReturn

Task/Apply-a-callback-to-an-array/AppleScript/apply-a-callback-to-an-array.applescript

@@ -1,11 +0,0 @@
-on callback for arg
-	-- Returns a string like "arc has 3 letters"
-	arg & " has " & (count arg) & " letters"
-end callback
-
-set alist to {"arc", "be", "circle"}
-repeat with aref in alist
-	-- Passes a reference to some item in alist
-	-- to callback, then speaks the return value.
-	say (callback for aref)
-end repeat