I'm trying to write a program which can solve a maze in PDDL, for example by using graphplan. From the examples I have seen on the internet one gets A solution to the problem(e.g. PDDL Graphplan can't find plan), but only one. I have some specific restrictions on my project which requires me to get ALL possible solutions to solve the maze and then evaluate theses solutions separately. Is this possible?
PDDL is a specification for describing problems, it has nothing to do with the output. The implementation of the search system is in charge of returning the results. For most of the competitions that use PDDL, they only require a single plan for the result and so many of the planning systems out there return only a single result (the ones I've seen from the competitions). If you're rolling you're own, then you can just return all, or if the one you choose is open source, it's probably not that difficult to update it to support multiple optimal plans when found.