Hi All,
> I particularly like the vertical visual representation of the stack. In fact
> I think it is crucial. A stack is after all a "stack" and not some other
> structure.
I see your point here - the name "stack" is evocative of a vertical
orientation. Of course, the data structure itself doesn't have an innate
orientation. I don't want to argue about something so subjective, but perhaps
let me flesh out why thinking of Factor code as having a horizontal stack works
for me, in the hopes that it helps someone else think about Factor code:
When I was first learning to read and write Factor (the first concatenative
language I've learned) I was visualizing a vertical stack. I was thinking of
things as being on the "top" of the stack or "the next one below the top" and
so on, based on the usual notion of a stack. All Factor code, though, shows
items on the stack in a left-to-right manner. For example, stack effects show (
a b -- c ). When first trying to understand a word's effect, I kept having to
remind myself whether the top of the stack was on the left or right. Having a
horizontal orientation in code and a vertical one in my head was extra mental
effort.
When I started to focus less on a vertical stack and more on the idea of
concatenating words, this became much easier for me. When looking at a word ":
foo ( a b -- c ) swap / ;", I could imagine that when we call "1 2 foo", we
instead evaluate "1 2 swap /". As we evaluate this we can imagine: (with |
representing the top of the stack)
| 1 2 swap /
1 | 2 swap / ! literals just "move over"
1 2 | swap /
2 1 | / ! we can visually see this right from swap's effect ( x
y -- y x )
2 |
That is, since Factor code shows stack effects and word bodies in a
left-to-right manner, I found it easiest to keep them that way. Especially with
combinators like over ( x y -- x y x ), I find it begs to be read as though the
second x on the right-hand side has been stuck on to the right end of the stack.
On a side note: when Factor shows a data stack in the listener, it does it with
the top of the stack at the bottom.
Well, I hope that helps someone learning Factor.
- Jesse
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