September 2017 Update

Task/Filter/AppleScript/filter-3.applescript

@@ -1,30 +1,40 @@
 -- filter :: (a -> Bool) -> [a] -> [a]
--- filter :: (a -> Int -> Bool) -> [a] -> [a]
--- filter :: (a -> Int -> [a] -> Bool) -> [a] -> [a]
 on filter(f, xs)
-    script mf
-        property lambda : f
-    end script
-
-    set lst to {}
-    set lng to length of xs
-    repeat with i from 1 to lng
-        set v to item i of xs
-        if mf's lambda(v, i, xs) then
-            set end of lst to v
-        end if
-    end repeat
-    return lst
+    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
 
-
--- Ordinary AppleScript predicate function, rather than a script object
+-- TEST -----------------------------------------------------------------------
 
 -- isEven :: (a -> Bool)
 on isEven(x)
     x mod 2 = 0
 end isEven
 
-set lstRange to {0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10}
+on run
 
-filter(isEven, lstRange)
+    filter(isEven, {0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10})
+
+    -- {0, 2, 4, 6, 8, 10}
+end run
+
+-- GENERIC FUNCTION -----------------------------------------------------------
+
+-- 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