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RELEASE NOTES Ragel 6.X
This file describes the changes in Ragel version 6.X that are not backwards
compatible. For a list of all the changes see the ChangeLog file.
Leaving Actions in Scanners (new in 6.1)
========================================
Scanners now ensure that any leaving actions at the end of a pattern are
executed. They are always executed before the pattern action.
The EOF Event
=============
There is a new execution variable called "eof". This should be set to pe on the
execution of the last buffer block. When p == eof the state machine's EOF
actions are executed. The variable is required only when EOF actions have been
embedded.
The advantage of this over "write eof" is that EOF actions are now executed in
the same context as regular actions. They are free to manipulate p, and jump to
a new portion of the machine to reprocess input. This was not possible with
"write eof".
The "write eof" directive was consequently removed.
Scanners now use EOF actions to to flush out the last token, if needed. This
eliminates the need to manually flush the last token.
Semantics of > % and Error Actions
==================================
Ragel has gone back to the 3.X semantics for >, % and error actions.
Those that have been using Ragel since the 3.X days will remember that the
entering operator > embedded a leaving action/priority into the start state
when it was final. The leaving operator % would embed EOF actions when the
final states stayed final all the way to the end of compilation. Also, error
actions would embed EOF actions when at the end of compilation the states the
error actions were embedded into were not final.
The problem before was that EOF actions and regular actions were executed in
different contexts ("write exec" and "write eof"), and a single action block
could easily end up in two different functions. This could lead to compile
errors and other subtle errors. Now that all actions are executed in the same
context ("write exec") these problems go away. The original semantics has been
restored.
Backend Automatically Executed
==============================
The "ragel" program now automatically executes the appropriate backend. If you
need the intermediate XML format you can use the -x option.
The fbreak Statement
====================
The fbreak statement now advances p. It is now possible to break out of the
machine and restart it without having to fix p first. Originally, fbreak did
not advance p because it was intended to be used to terminate processing.
Advancing p was more work than necessary in that case. But fbreak turns out to
be useful for stopping to return a token as well. In this case the failure to
advance p is an inconvenience.
Guarded Concatenation Operators are Stronger
============================================
The :> :>> and <: guarded concatenation operators have been strengthened. In
the previous version of Ragel is was possible for the priority assignments to
be bypassed via the the zero length string. Running the following examples
through 5.25 you will see that the a and b actions are executed on a single
transition, showing the guard fails. This happens because the operators did not
consider that the middle machine might have a start state that is final. In 6.0
these cases have been fixed.
(' '@a)* <: 'x'* . ' '@b;
(' '@a)* :> 'x'? . ' '@b;
(' '@a)* :>> 'xyz'? . ' '@b;
The tokstart and tokend Variables Renamed
=========================================
The "tokstart" and "tokend" variables were changed to "ts" and "te". These
variables get referenced a lot in scanner actions. They should be shorter.
To update your code simply search and replace:
tokstart => ts
tokend => te
Options
=======
The -l option in rlgen-cd was changed to -L because -l is used in the frontend,
which now must pass options through.
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