Hyphens are extensively used in existing benchmarks. If I got my regex right, 111 out of 114 files with the name "domain.pddl" in our benchmark repository use hyphens as part of a symbol. (For comparison, 30 out of 114 use underscores.)

They also occur in symbols with special meaning in PDDL such as the fluent "total-cost", most of the requirements ("action-costs", "negative-preconditions" etc.) and PDDL syntax like ":durative-action". This is because Lisp traditionally uses hyphens in names where most current programming languages use underscores.

Currently there is no check if e. g. predicate names or object names contain forbidden symbols.

We would like to implement stricter syntax checking. For this we should first define what syntax is allowed, e. g. according to the PDDL book "Names made up of alphanumeric characters (a-z,0-9) and underscores (_) should be acceptable to all planners." McDermott et al., 1998 also allow hyphens (-) though.

Also we need to differentiate between variables which always start with a question mark and other names.