Let's say you write some code that handles numbers differently, say a library that implements quaternion math. For doing graphics manipulations. Then you try to use it with tensorflow maybe for some ai-driven optimization. Is it going to work? Probably not out of the box. You will have to do some munging of quaternion data type to shove them into tensorflow tensors. Do the same thing in Julia with Julia's flux, it probably will, and maybe even with the gpu That's the difference.