Forth (or Postscript by the way) works exactly like that, but writing the function first also makes sense in functional programming, specifically when you care about currying functions: writing "f(g(h(x)))" (or "f g h x" or whetever) makes more sense, since you are not supposed to put all expected arguments at once.

Do you have to write a function first before it is referenced in PostScript? (I did a lot of PostScript programming in NeWS once - but it was ~35 years ago...)