J's arrays are homogeneously typed, for example the list 1 2 3 is a list of integers despite 1 being a bit. For the most part, these sorts of type issues are transparent to programmers. Only certain specialized operations reveal differences in type. For example, the list 1.0 0.0 1.0 0.0 would be treated exactly the same, by most operations, as the list 1 0 1 0 .
