Comment by DonaldFisk

This helps the compiler, but only works for languages with type declarations, and is less helpful to the programmer, as to find a variable's kind (e.g. valid data vs. raw data) you need to look at its declaration, which may involve scrolling. The original idea, described in Joel Spolsky's original article on Apps vs. Systems Hungarian (https://www.joelonsoftware.com/2005/05/11/making-wrong-code-...) is that the programmer can see, in the expression that the variable is used or the function is called, that the code is wrong.

I apply a variant of Apps Hungarian in my own code, e.g.

    (setf input
          (inputOfEdge 
           (first (edgesOfSocket
                   (outputOfGate
                    (nth (position visibleInput (inputsOfVertex node))
                         (ingatesOfEnclosure enclosure)))))))

(In the system this is lifted from, node was confirmed to be a Vertex a few lines earlier, and Output is a subclass of Socket.)

The general idea is language independent: you could write similar code in Java or C.