Obviously order does matter here, since ‘Monoid’ instance for ‘Hints’ is
derived from [], so (<>) is the same as (++) and we should be careful
to keep things in the right order.
If ‘x’ in ‘x >>= y’ consumes input but produces some hints, we should
accumulate them nonetheless. Why it's important can be demonstrated by
the following test:
many (char 'a') >> many (char 'b') >> eof
This should fail on input "ac" with the following message:
parse error at line 1, column 2:
unexpected 'c'
expecting 'a', 'b' or end of input
As you can see even though parser ‘many (char 'a')’ consumed input, its
hits may be useful later.
* Removed ‘optionMaybe’ parser, because ‘optional’ from
‘Control.Applicative’ does the same thing.
* Renamed ‘tokenPrim’ → ‘token’, removed old ‘token’, because
‘tokenPrim’ is more general and ‘token’ is little used.
* Fixed bug with ‘notFollowedBy’ always succeeded with parsers that
don't consume input, see #6.
* Hint system introduced that greatly improved quality of error messages
and made code of ‘Text.Megaparsec.Prim’ a lot clearer.
The improvements affected other modules too:
* Some parsers from ‘Text.Megaparsec.Combinators’ now live in
‘Text.Megaparsec.Prim’.
* Hint system improved error messages, so I needed to rewrite test for
‘Text.Megaparsec.Char.eol’, since it's error messages are very
intelligent now and cannot be emulated by ‘newline’ and ‘crlf’ parsers
used separately.
* Test for Bug9 from old-tests is passed successfully again.
