levels of forth --
level 1: stack manipulation words and reverse polish notation
level 1.5: using the return stack for temporary storage
level 2 (dark path): control flow via return stack manipulation
level 2 (light path): control flow via control flow words
level 3: metaprogramming with immediate and postpone
level 3.5 (dark path): immediate words that parse the input buffer
level ∞ (dark path): rolling your own string literal word s" that works in both compiler and interpreter mode