Close#95.
Here we introduce ‘scientific’ parser that can parse arbitrary big
numbers without error or memory overflow. ‘float’ still returns
‘Double’, but it's defined in terms of ‘scientific’ now. Since
‘Scientific’ type can reliably represent integer values as well as
floating point values, ‘number’ now returns ‘Scientific’ instead of
‘Either Integer Double’ (‘Integer’ or ‘Double’ can be extracted from
‘Scientific’ value anyway). This in turn makes ‘signed’ parser more
natural and general, because we do not need ad-hoc ‘Signed’ type class
anymore.
This should improve experience of users who use Megaparsec with Alex and
Happy. The commit also introduces some minor changes in
‘Text.Megaparsec.Pos’ module (improving argument order).
This was Parsec's legacy that we should eliminate now. ‘Message’ does
not constitute enumeration, ‘toEnum’ was never properly defined for
it. The idea to use ‘fromEnum’ to determine type of ‘Message’ is also
ugly, for this purpose new functions ‘isUnexpected’, ‘isExpected’, and
‘isMessage’ are defined in ‘Text.Megaparsec.Error’.
In particular, if input has no newline at the end, we need to treat it
specially, because otherwise we will get confusing “incorrect
indentation” message.
After some thinking I decided that this may be not desirable in some
cases, so we should not enable it by default. I've edited documentation
of ‘makeExprParser’ to explain why this doesn't work by default and how
to make it work.
Close#64.
‘makeExprParser’ now generates parser that can handle several
occurrences of the same prefix or postfix operator in a row. This allows
to parse something like C pointers (for example ‘**i’) without resorting
to hacks.
The feature is experimental, I'm not entirely sure it's not
buggy. Upcoming additional tests for ‘Text.Megaparsec.Expr’ will show
whether it behaves correctly in all cases and doesn't have adverse
effects. For now, I've edited existing test to generate data with
repeating prefix negations and postfix factorials. Current code-base
passes the test.
