†を()に

†.hs

import Data.List

parens 0 = [""]
parens n = [ x ++ y
           | a <- [0..n-2]
           , let b = n-2-a
           , x <- map ('(':) (parens a)
           , y <- map (')':) (parens b)
           ]

merge c s1 s2 = snd $ mapAccumL f s1 s2
  where
    f (x:xs) c' | c == c' = (xs,x)
    f xs c' = (xs,c')

solve c xs = [ merge c ys xs | ys <- parens $ length $ elemIndices c xs ]

f = solve '†'