More general

app/7.hs

@@ -8,21 +8,16 @@ data D = D { target :: Int, parts :: [Int]}
 parse :: String -> [D]
 parse = ((\(a:as) -> D (read $ takeWhile (/= ':') a) (read <$> as)) . words <$>) . lines
 
-canBeTarget :: Int -> [Int] -> Bool
-canBeTarget _ [] = False
-canBeTarget t [x] = t == x
-canBeTarget t (x:y:xs) = any (canBeTarget t) [x+y:xs, x*y:xs]
+canBeTarget :: Int -> [Int -> Int -> Int] -> [Int] -> Bool
+canBeTarget _ _   [] = False
+canBeTarget t _   [x] = t == x
+canBeTarget t ops (x:y:xs)  = any (canBeTarget t ops . (:xs)) ((uncurry <$> ops) <*> pure (x,y))
 
 solve1 :: [D] -> Int
-solve1 = sum . (target <$>) . filter (\(D t p) -> canBeTarget t p)
-
-canBeTarget' :: Int -> [Int] -> Bool
-canBeTarget' _ [] = False
-canBeTarget' t [x] = t == x
-canBeTarget' t (x:y:xs) = any (canBeTarget' t) [x+y:xs, x*y:xs, read (show x ++ show y):xs]
+solve1 = sum . (target <$>) . filter (\(D t p) -> canBeTarget t [(*), (+)] p)
 
 solve2 :: [D] -> Int
-solve2 =  sum . (target <$>) . filter (\(D t p) -> canBeTarget' t p)
+solve2 =  sum . (target <$>) . filter (\(D t p) -> canBeTarget t [(*), (+), \a b -> read (show a ++ show b)] p)
 
 main :: IO ()
 main = readFile "inputs/7" <&> parse >>= \i ->