Sorry for the delay, the branch is now merged.

Looks good. I made another change so that we also discard other actions with
empty effect (i.e., ":effect (and)") and so that the final syntax test is not
skipped if we have ":effect ()". If you're happy with the latest changeset,
please merge.

Discarding actions with an empty effect during parsing requires only a minor
change in the code. Malte, I pushed a patch to the issue412 branch. Should we
merge this?

The patch looks good. Thanks Malte! Before I merge it, I just would like to ask
whether it wouldn't make sense to directly discard actions without an effect
when parsing them. Is there any use case of a translator-variant where we would
need them?

I pushed a patch to the issue412 branch of the master repository.
Gabi, does it look OK to you?

Dear Yan,

thanks for letting us know!

Checking the PDDL 3.0 BNF, I have found two places where empty lists are allowed
and we don't currently support them: :precondition and :effect. They don't seem
to be allowed in :goal or in the condition part of conditional effects.

It's probably a good idea to fix both of these at the same time. We'll look into it.

Hi all,

we have found out that the translator script fails to parse actions with empty 
preconditions like this:

(:action action-name                                                              
    :parameters ()
    :precondition ()
    :effect     (something)                                                                  
)

It produces the following error message:

  File "src/translate/pddl/conditions.py", line 17, in parse_condition_aux
    tag = alist[0]
IndexError: list index out of range

It seems to us that an empty precondition list is a valid PDDL syntax.  We have 
created a patch that you can find attached.  Use it at your will.

Sincerely,

yan