We've split the non-associative exceptions into the base class, X::Syntax::NonAssociative, with a subclass off X::Syntax::NonListAssociative. nqp's EXPR now calls a different method to fail list associativity, and rakudo provides the alternate method to get the appropriate message.
nqp fix in 9073af7ab6049485a245fce383a034a41603cfd8 rakudo fix in f568db26f85909a2431325491405fea6a1efed87 tests in 5939e74f80322a1288fbd891b24311186b015eb8
