Add hlint warning

lang/app/Main.hs

@@ -7,7 +7,7 @@ append xs ys = λ xs . λ ys . case xs of
     Nil => ys
     Cons x' xs' => Cons x' (append xs' ys)
 -}
-f x y = (x + y)
+f = concat $ map (+ 1) [1, 2, 3]
 
 bodyOfAppend :: Expression
 bodyOfAppend =