How to hack GHCi (or Hugs) so that it prints Unicode chars unescaped?

Question

Look at the problem: Normally, in the interactive Haskell environment, non-Latin Unicode characters (that make a part of the results) are printed escaped, even if the locale

Answer 1

Option 1 (bad):

Modify this line of code:

https://github.com/ghc/packages-base/blob/ba98712/GHC/Show.lhs#L356

showLitChar c s | c > '\DEL' =  showChar '\\' (protectEsc isDec (shows (ord c)) s)

And recompile ghc.

Option 2 (lots of work):

When GHCi type checks a parsed statement it ends up in tcRnStmt which relies on mkPlan (both in https://github.com/ghc/ghc/blob/master/compiler/typecheck/TcRnDriver.lhs). This attempts to type check several variants of the statement that was typed in including:

let it = expr in print it >> return [coerce HVal it]

Specifically:

print_it  = L loc $ ExprStmt (nlHsApp (nlHsVar printName) (nlHsVar fresh_it))
                                      (HsVar thenIOName) placeHolderType

All that might need to change here is printName (which binds to System.IO.print). If it instead bound to something like printGhci which was implemented like:

class ShowGhci a where
    showGhci :: a -> String
    ...

-- Bunch of instances?

instance ShowGhci Char where
    ...  -- The instance we want to be different.

printGhci :: ShowGhci a => a -> IO ()
printGhci = putStrLn . showGhci

Ghci could then change what is printed by bringing different instances into context.