CFengine Parser

[Bas van der Vlies]

I find cfengine3 much better then previous version (1 and 2), The only main 
concern for me is the parser and how it reports syntax
errors, Previous cfengine versions had the same problem. A lot can improved in 
this area. The syntax for cfengine is clear and can
easily be checked. It will also be easier for starters when syntax errors are 
reported in a better way (See c-ompiler). I see a lot
of people spending hours of debugging and mostly they have spelling errors or 
forgot a keyword.

Here are a few examples to show how it could improved.

the keyword 'bundle` can only have a few values:
  * common| agent | server | edit_line | ..

So for the lexer/parser is must be easy to find out when an invalid keyword is 
used, eg:
  bundle comon maui
  {
    vars:
        any::

            "dir"           string => "/var/spool/maui";
            "default_file"  string => "/etc/default/maui";

        debian::
            "restart"       string => "/usr/sbin/service maui restart";
  }

cf-promises see this as valid syntax. It should report:
  * comon is unknown keyword for bundle, and maybe have some suggestions

This also holds for body. You can declare bodies that are unknown to cfengine, 
eg:
  body edit_lines jaap
  {
     select_field    => "2";
  }

cf-promisses should report 'edit_lines' is an unknown body.


Sometimes i forgot a keyword:
  bundle common maui
  {
    vars:
        any::

            "dir"           => "/var/spool/maui";
  }

For a parser it must be easy to detect that a keyword is missing, namely the 
type of the variable.



In cfengine3 there is some syntax checking. If you make an spelling error in 
the body then cf-promises does the right thing:
  body edit_line jaap
  {
    select_fields    => "2";
  }

  14:07 install2:/var/tmp/bas/cfengine/cf-config
  root# cf-promises  -f ./promises.cf
  cf3> ./bundles/maui.cf:19,27: Constraint lvalue "select_fields" is not 
allowed in 'edit_line' constraint body, near token '2"'


It would be nice if the kind of checking could be done for other sections.

-- 
********************************************************************
*  Bas van der Vlies                    e-mail: b...@sara.nl       *
*  SARA - Academic Computing Services   Amsterdam, The Netherlands *
********************************************************************

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