Caught should be internal

[shajra]

This example shows how we can use Caught directly to bypass safety:

{-# LANGUAGE FlexibleContexts #-}


module Main where


import           Control.Exception.Checked
import           Control.Monad
import           Data.Proxy


falseSecurity :: Throws IOException e => CheckedIO e String
falseSecurity =
    throws' (Proxy :: Proxy IOException) $ readFile "no file here"

harshReality :: CheckedIO (Caught IOException e) String
harshReality = falseSecurity

-- explodes
main :: IO ()
main = void $ runChecked harshReality

This doesn't use fancy extensions that have come out since the 2009 paper Explicitly Typed Exceptions for Haskell, so the problem was there even in the original work. And this paper suggests exposing Caught to support explicitly typed user-created exception hierarchies. So in a way, we want to expose Caught as an implementation detail that can be extended. But we also want to discourage users from trying to use it directly.

So I'm thinking I'll create an “Internal” module with everything, and then re-export what's safe out in the normal module.