Typo fixing suggestions based on the Levenshtein distance

suggestion.hs

import Data.List   (sortOn)
import Text.Printf (printf)

type Env a  = [(String, a)]
type Dist a = a -> a -> Int

lev :: Dist String
lev  x      ""    = length x
lev  ""     y     = length y
lev (x:xs) (y:ys) = if x == y
  then lev xs ys
  else 1 + minimum [lev (x:xs) ys, lev xs (y:ys), lev xs ys]

sortEnv :: Env a -> Dist String -> String -> Env a
sortEnv env dist str = sortOn (dist str . fst) env

put :: String -> a -> Env a -> Env a
put str val env = (str, val) : env

getS :: Dist String -> Env a -> String -> Either String a
getS dist env str = case sortEnv env dist str of
  []         -> Left $ printf "Couldn't find %s." str
  (s, x) : _ -> if s == str then Right x else Left msg
    where msg = printf "Couldn't find %s. Did you mean %s?" str s