Unclear semantics of `Error.unread`

[lrworth]

It is not clear whether Error.unread is meant to be given an error message or the value that produced an error.

On one hand, we have char that contains this snippet:

Error.unread "must be a one-character string"

On the other hand, we have this error message template in handleUnreadError:

fmap (\val -> indent 2 (name ++ " has value " ++ val ++ " that cannot be parsed")) . Error.tryUnread

This results in the following confusing error printed to the console:

MY_VARIABLE has value must be a one-character string that cannot be parsed