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import qualified Data.Foldable as F
import Control.Monad
import Control.Monad.Instances
 
monkeyNum :: Integer -> Integer
monkeyNum = F.foldMap ((^ 5) . read . (:[])) . show
 
isMonkey :: Integer -> Bool
isMonkey = monkeyNum >>= (==)
 
main :: IO ()
main = print $ sum $ filter isMonkey [10..99999]
 

[1 of 1] Compiling Main             ( prog.hs, prog.o )

prog.hs:6:12:
    No instance for (Data.Monoid.Monoid Integer)
      arising from a use of `F.foldMap' at prog.hs:6:12-43
    Possible fix:
      add an instance declaration for (Data.Monoid.Monoid Integer)
    In the first argument of `(.)', namely
        `F.foldMap ((^ 5) . read . (: []))'
    In the expression: F.foldMap ((^ 5) . read . (: [])) . show
    In the definition of `monkeyNum':
        monkeyNum = F.foldMap ((^ 5) . read . (: [])) . show

Standard output is empty