Stack notation: "<stack before> -- <stack after>". Rightmost is top of stack
                (TOS). For example, in "a b -- c d", b is TOS before, d is TOS
                after. "R:" means that the Return Stack is modified.

: x ... ;   --              Define a new word
.           n --            Print n in its decimal form
@           a -- n          Set n to value at address a
!           n a --          Store n in address a
+           a b -- c        a + b -> c
-           a b -- c        a - b -> c
*           a b -- c        a * b -> c
/           a b -- c        a / b -> c
CREATE x    --              Create cell named x
EMIT        c --            Spit char c to stdout
EXECUTE     a --            Execute word at addr a
EXIT        R:I --          Exit a colon definition
HERE        -- a            Push HERE's address
QUIT        R:drop --       Return to interpreter promp immediately
KEY         -- c            Get char c from stdin
INTERPRET   --              Get a line from stdin, compile it in tmp memory,
                            then execute the compiled contents.