When the typesystem fails

stat.purs

module Main where

import Prelude
import Control.Monad.Eff (Eff)
import Control.Monad.Eff.Console (CONSOLE, log)
import Control.Monad.Eff.Exception (EXCEPTION, Error, catchException, message)

import Node.FS (FS)
import Node.FS.Sync (stat)

import Data.Traversable (traverse)
import Data.Either (Either(..))

catch :: forall a eff. Eff ( err :: EXCEPTION | eff ) a -> Eff eff (Either Error a)
catch e = catchException (pure <<< Left) (e >>= pure <<< Right)

arr :: Array String
arr = ["these", "do", "not", "exist"]

main :: forall e. Eff (console :: CONSOLE, fs :: FS | e) Unit
main = do
  xs <- catch $ traverse stat arr
  case xs of
      Left err -> log $ message err
      _ -> log "success!"