June 2018 Update

Task/Greatest-element-of-a-list/AppleScript/greatest-element-of-a-list-2.applescript

@@ -1,9 +1,9 @@
--- maximumBy :: (a -> a -> Ordering) -> [a] -> a
-on maximumBy(f, xs)
+-- maximumByMay :: (a -> a -> Ordering) -> [a] -> Maybe a
+on maximumByMay(f, xs)
     set cmp to mReturn(f)
     script max
         on |λ|(a, b)
-            if a is missing value or cmp's |λ|(a, b) < 0 then
+            if cmp's |λ|(a, b) < 0 then
                 b
             else
                 a
@@ -11,8 +11,8 @@ on maximumBy(f, xs)
         end |λ|
     end script
 
-    foldl(max, missing value, xs)
-end maximumBy
+    foldl1May(max, xs)
+end maximumByMay
 
 -- TEST -----------------------------------------------------------------------
 on run
@@ -34,16 +34,33 @@ on run
         end |λ|
     end script
 
-    return {¬
-        maximumBy(comparing(|length|), lstWords), ¬
-        maximumBy(comparing(population), lstCities)}
+
+    return catMaybes({¬
+        maximumByMay(comparing(|length|), lstWords), ¬
+        maximumByMay(comparing(|length|), {}), ¬
+        maximumByMay(comparing(population), lstCities)})
 
     --> {"epsilon", {name:"Shanghai", population:24.15}}
+
 end run
 
 
 -- GENERIC FUNCTIONS ----------------------------------------------------------
 
+-- catMaybes :: [Maybe a] -> [a]
+on catMaybes(mbs)
+    script emptyOrListed
+        on |λ|(m)
+            if nothing of m then
+                {}
+            else
+                {just of m}
+            end if
+        end |λ|
+    end script
+    concatMap(emptyOrListed, mbs)
+end catMaybes
+
 -- comparing :: (a -> b) -> (a -> a -> Ordering)
 on comparing(f)
     set mf to mReturn(f)
@@ -64,23 +81,62 @@ on comparing(f)
     end script
 end comparing
 
--- foldl :: (a -> b -> a) -> a -> [b] -> a
-on foldl(f, startValue, xs)
+-- concatMap :: (a -> [b]) -> [a] -> [b]
+on concatMap(f, xs)
+    set acc to {}
     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)
+        repeat with x in xs
+            set acc to acc & |λ|(contents of x)
         end repeat
-        return v
     end tell
-end foldl
+    return acc
+end concatMap
+
+-- foldl1May :: (a -> a -> a) -> [a] -> Maybe a
+on foldl1May(f, xs)
+    set lng to length of xs
+    if lng > 0 then
+        if lng > 1 then
+            tell mReturn(f)
+                set v to item 1 of xs
+                set lng to length of xs
+                repeat with i from 2 to lng
+                    set v to |λ|(v, item i of xs, i, xs)
+                end repeat
+                return just(v)
+            end tell
+        else
+            just(item 1 of xs)
+        end if
+    else
+        nothing("Empty list")
+    end if
+end foldl1May
+
+-- just :: a -> Just a
+on just(x)
+    {nothing:false, just:x}
+end just
 
 -- length :: [a] -> Int
 on |length|(xs)
     length of xs
 end |length|
 
+-- max :: Ord a => a -> a -> a
+on max(x, y)
+    if x > y then
+        x
+    else
+        y
+    end if
+end max
+
+-- nothing :: () -> Nothing
+on nothing(msg)
+    {nothing:true, msg:msg}
+end nothing
+
 -- Lift 2nd class handler function into 1st class script wrapper
 -- mReturn :: Handler -> Script
 on mReturn(f)