I've been trying to write a bunch of Forth, and I've gotta say stack comments (essentially type signatures, though typically not checked) are invaluable; that,

I've been trying to write a bunch of Forth, and I've gotta say stack comments (essentially type signatures, though typically not checked) are invaluable; that, and making definitions small enough that you can verify that they're obviously correct within a few seconds. (Typically, most definitions are one-liners.)