Ragel 6.0 Changes
=================

Remove old action embedding and condition setting syntax.

Expressions of the form: ( expr1 <: expr2 . expr3 ) sometimes don't behave as
expected. If expr2 contains the empty string then it's possible for the machine
to escape to expr3. This is somewhat unexpected.  The empty string does count
as moving through the right machine so there should not be an exception for
this case. Using the stronger implementation: ( expr1 $1 %0 . expr2 ) will
solve the problem.

Also, there is potential for nondeterminism to persist via the empty string
with the :> and :>> operators. Should also guard against this using leaving
priorities.

fbreak should advance the current char. Depreciate fbreak and add
    fctl_break;
    fctl_return <expr>;
    fctl_goto <label>;

fbreak should execute the to-state actions of the target state. The semantics
of fbreak should be identical to reaching the end of a buffer block.

Introduce a new variable "eof" which is a pointer like pe. It gets set to pe
when the input has ended. This would enable eof actions to go into the main
loop, granting them the ability to manipulate p and cs. This would free us from
requiring some eof character to be sent to scanners to 'flush out' the last
token.  Instead an eof action can now execute scanner pattern actions and
backtrack if necessary.

The tokstart/tokend variable should be shortened to ts/te.

Eliminate tokend, replace it with the marker variable and add ftokend/ftoklen.

Add the accept action embedding operator: like eof but only for states that end
up final. Add the combined pending/accept action. This becomes a good idea when
eof action execution is moved into the main loop.

Include file searching should be relative to the source file. Should add a -I
option.

================
END 6.0 Features

Add a prefix operator which sets every state final.

Minimization should remove a condition when the character allows both
the positive and negative sense of the condition. This happens in:
test_every_10_chars = ( ( c when test_len ) c{0,9} )**;
In this example there is non-determinsm that is killed by the priorities, but
since conditions are expanded before priorities are tested, many transitions
end up with test_len || !test_len.

Should be possible to include scanner definitions in another scanner.

Need an "entry name;" feature, causing name to get written out with the other
entry points in the data.

Possibly bring back the old semantics of > in a new operator, or allow it to be
defined somehow.

When priorities are embedded without a name, the name of the current machine is
used. Perhaps a unique name for each instance of the current machine should be
used instead. This idea could work well if applied to user-defined embeddings. 

User defined embeddings <-name(a1,a2,...).
User defined operators expr1 <name> expr2.

Doesn't make make sense for [] to be the lambda (zero-length) machine. This
should be the empty set (the empty machine). But then would it be invalid in a
regular expression?

The |> guarded operator and the <| guarded operator need to be added.

An option to turn off the removal of duplicate actions might be useful for
analyzing unintentional nondeterminism.

Might be a good idea to add in some protection against using up all of a
system's memory. This protection could then be removed by people when someone
is sure they want to use a lot of memory.


If a scanner can be optimized into a pure state machine, maybe permit it to be
referenced as a machine definition. Alternately: inline scanners with an
explicit exit pattern.

The split codegen needs a profiler connected to a graph partitioning algorithm.

Die a graceful death when rlcodegen -F receives large alphabets.

It's not currently possible to have more than one machine in a single function
because of label conflicts. Labels should have a unique prefix.

Emit a warning when a subtraction has no effect.

Emit a warning when unnamed priorities are used in longest match machines.
These priorities may unexpectedly interact across longest-match items. Changing
the language such that unwated interaction cannot happen would require naming
longest-match items.

Testing facilities: Quick easy way to query which strings are accepted.
Enumerate all accepted strings. From Nicholas Maxwell Lester.

Add more examples, add more tests and write more documentation.

A debugger would be nice. Ragel could emit a special debug version that
prompted for debug commands that allowed the user to step through the machine
and get details about where they are in their RL.

A quick and easy alternative would be a trace code generation option. This
would open a trace file and list all the active machines at each step of the
input.

Frontend should allow the redefinition of fsm section delimiters.

Do more to obscure ragel's private variables. Just a leading underscore is not
enough. Maybe something more like __ri__.

Some talk about capturing data:

Separate tokstart/tokend from the backtracking.  One var for preservation,
called preserve.  Write delcarations;  produces the necessary variables used by
ragel.  Move pattern start pattern end concepts into the general?  The
variables which may need to influence the preserve is dependent on the state.
States have a concept of which variables are in use.  Can be used for length
restrictions.  If there is an exit pattern, it is the explicit way out,
otherwise the start state and all final states are a way out.