September 2017 Update

Task/Sort-using-a-custom-comparator/AppleScript/sort-using-a-custom-comparator.applescript

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+use framework "Foundation"
+
+-- SORTING LISTS OF ATOMIC (NON-RECORD) DATA WITH A CUSTOM SORT FUNCTION
+
+-- In sortBy, f is a function from () to a tuple of two parts:
+-- 1. a function from any value to a record derived from (and containing) that value
+--  The base value should be present in the record under the key 'value'
+--  additional derivative keys (and optionally the 'value' key) should be included in 2:
+-- 2. a list of (record key, boolean) tuples, in the order of sort comparison,
+--    where the value *true* selects ascending order for the paired key
+--    and the value *false* selects descending order for that key
+
+-- sortBy :: (() -> ((a -> Record), [(String, Bool)])) -> [a] -> [a]
+on sortBy(f, xs)
+    set {fn, keyBools} to mReturn(f)'s |λ|()
+    script unWrap
+        on |λ|(x)
+            value of x
+        end |λ|
+    end script
+    map(unWrap, sortByComparing(keyBools, map(fn, xs)))
+end sortBy
+
+-- SORTING APPLESCRIPT RECORDS BY PRIMARY AND N-ARY SORT KEYS
+
+-- sortByComparing :: [(String, Bool)] -> [Records] -> [Records]
+on sortByComparing(keyDirections, xs)
+    set ca to current application
+
+    script recDict
+        on |λ|(x)
+            ca's NSDictionary's dictionaryWithDictionary:x
+        end |λ|
+    end script
+    set dcts to map(recDict, xs)
+
+    script asDescriptor
+        on |λ|(kd)
+            set {k, d} to kd
+            ca's NSSortDescriptor's sortDescriptorWithKey:k ascending:d selector:dcts
+        end |λ|
+    end script
+
+    ((ca's NSArray's arrayWithArray:dcts)'s ¬
+        sortedArrayUsingDescriptors:map(asDescriptor, keyDirections)) as list
+end sortByComparing
+
+
+-- GENERIC 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 |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
+
+
+-- TEST ----------------------------------------------------------------------
+on run
+    set xs to ["Shanghai", "Karachi", "Beijing", "Sao Paulo", "Dhaka", "Delhi", "Lagos"]
+
+    -- Custom comparator:
+
+    -- Returns a lifting function and a sequence of {key, bool} pairs
+
+    -- Strings in order of descending length,
+    -- and ascending lexicographic order
+    script lengthDownAZup
+        on |λ|()
+            script
+                on |λ|(x)
+                    {value:x, n:length of x}
+                end |λ|
+            end script
+            {result, {{"n", false}, {"value", true}}}
+        end |λ|
+    end script
+
+    sortBy(lengthDownAZup, xs)
+end run