@neongreen I think the problem with pretty-simple is two-fold:

pretty-simple doesn't handle non-balanced brackets: allow non-balanced brackets, parens, etc #27. Here's the expression that "[']']" is parsed into:
```
[ Brackets 
    ( CommaSeparated 
        { unCommaSeparated = 
            [ [ Other "'" ] ]
        }
    )
, Other "'" 
]
```
Basically this means there are brackets surrounding a ', and then a single '. The final bracket is removed. The reason there are spaces around the first quote is that pretty-simple prints spaces inside of brackets by default.

This should instead be parsed into something like this:
```
[ Brackets 
    ( CommaSeparated 
        { unCommaSeparated = 
            [ [ CharLit ']' ] ]
        }
    )
]
```
pretty-simple doesn't have a special parser for Haskell characters (e.g. things like 'a' or 'X' or ']'). So it doesn't realize that ']' is supposed to be a character (and not a closing bracket).

It would be nice to add an expression for characters (like the CharLit I've used above).

If you want to send a PR fixing either of these things, it would definitely be accepted!

If you wanted to fix this, you'd mainly have to edit the expression parser, which lives in these two files:

the parser doesn't understand Haskell characters like 'a' #45

Description