peter brinkmann is the guy who who would know best, but i seem to remember pretty clearly that he stated somewhere [expr] and [expr~] were ok to use with libPD on the AppStore. in other words (i assume) they had been recompiled from source in
a more compatible license.
here's the bit that clearly states that the vanilla version of PD does not have the right version of [expr] and [expr~] this is older news from about 2011 i think:
and here's the bit where they mention [expr] and [expr~] are now under LGPL, but it doesn't appear to solve the issue definitively:
the total solution if you want that specific functionality (that i am aware of) is to recompile [expr] and [expr~] from source and put it under a BSD or MIT license.
the alternative is to redo that functionality with simple vanilla objects. there's a nice thread her on the PD forum about it:
hope this helps somewhat,
best,
scott