T5283.hs 502 Bytes
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{-# LANGUAGE Arrows #-}
-- Failed in ghci

module T where

import Prelude
import Control.Arrow

mapAC :: Arrow arr => Integer -> arr (env, b) c -> arr (env, [b]) [c]  
mapAC n farr = go 1
  where
    go i | i == succ n = arr (\(_env, []) -> [])
         | otherwise = proc ~(env, b : bs) ->
             do c  <- farr -< (env, b)
                cs <- go (succ i) -< (env, bs)
                returnA -< c : cs

t :: Arrow arr => arr [a] [a]
t = proc ys ->
     (| (mapAC 3) (\y -> returnA -< y) |) ys