We used juel as an expression language EL implementation in one our projects. The problem we had, was that we could not afford waiting for the expression to be checked at runtime. For example if you are accessing a pojo field, and that field does not exist, they you only know it in runtime.
To fix this, I created an extension and added a validate method. This method traverses the tree and checks all possible options to make sure the expression is valid with given objects.
I offered the new extention to the community, but they thought it is better to keep the Juel to minimum required to match the standard.
I am going to publish as an extension to Juel in seperate branch. Maybe someone else also can make use of it. Not planned yet though.