> *A Typeclass for user-facing output*
## Description
The `text-display` library offers a way for developers to print a textual representation of datatypes that does not
have to abide by the rules of the [Show typeclass][Show].
If you wish to learn more about how things are done and why, please read the [DESIGN.md](https://github.com/haskell-text/text-display/blob/main/DESIGN.md) file.
## Examples
There are two methods to implement `Display` for your type:
The first one is a manual implementation:
```haskell
data ManualType = MT Int
-- >>> display (MT 32)
-- "MT 32"
instance Display ManualType where
displayPrec prec (MT i) = displayParen (prec > 10) $ "MT " <> displayPrec 11 i
```
But this can be quite time-consuming, especially if your datatype already has
an existing `Show` that you wish to reuse. In which case, you can piggy-back
on this instance like this:
```haskell
{-# LANGUAGE DerivingVia #-}
data AutomaticallyDerived = AD
-- We derive 'Show'
deriving Show
-- We take advantage of the 'Show' instance to derive 'Display' from it
deriving Display
via (ShowInstance AutomaticallyDerived)
```
But let's say you want to redact an instance of `Display`? You can do it locally, through
the `OpaqueInstance` helper. It is most useful to hide tokens or passwords:
```haskell
data UserToken = UserToken UUID
deriving Display
via (OpaqueInstance "[REDACTED]" UserToken)
display $ UserToken "7a01d2ce-31ff-11ec-8c10-5405db82c3cd"
-- => "[REDACTED]"
```
[Show]: https://hackage.haskell.org/package/base/docs/Text-Show.html#v:Show