The article’s argument is that it’s not a stack machine because entry of a block is a barrier for accessing what’s on the stack. (AFAIK, exiting a block also i

The article’s argument is that it’s not a stack machine because entry of a block is a barrier for accessing what’s on the stack. (AFAIK, exiting a block also is limited in that it can only return a single item) You can’t do what’s typical in forths: push intermediate values, enter a loop, use and/or change intermediate values, check for end of loop, loop or exit, read intermediate values. An example from http://www.murphywong.net/hello/simple.htm#L15 http://www.murphywong.net/hello/simple.htm#L15): : INTEGERS ( +n -- ) 1 \ Initialize i to 1 ( +n i=1 ) BEGIN \ Start loop: i is TOS ( +n i ) 2DUP \ Duplicate 2 items ( +n i +n i ) < \ Is +n less than i ? ( +n i flag ) IF \ Act on flag ( +n i ) 2DROP \ True: drop 2 items ( ) EXIT \ True: leave word ( ) THEN \ End IF ... THEN ( ) DUP \ DUPlicate TOS ( +n i i ) . \ Display TOS ( +n i ) 1+ \ Increment TOS ( +n i=i+1 ) AGAIN \ Loop back ( +n i ) ; \ End definition Here, both the value of n and the loop counter are on the stack when entering the loop, and the loop removes them before exiting (using 2DROP) Edit: you also can’t take multiple values from the stack in a loop, as in 111 108 108 101 72 5 0 DO EMIT LOOP which, if I didn’t mess things up, prints “Hello”.