Hi Maxim,
Factor is flexible enough that you can implement your proposal and
play around with it.
It should be possible to make it efficient too; locals don't have any
support from the compiler either.
Also note that Factor's locals library supports mutable locals too
(suffix the name with !, and use foo! to write; see the docs for
details).
Slava
On Apr 7, 2008, at 1:41 AM, Maxim Savtchenko wrote:
> I have mixed feelings about extra/locals library. It is good to have
> local named storage, but current design of extra/locals looks very
> "lispish" (FP-style immutable variables). I think, there is a way to
> make it closer to Factor stack-shuffling paradigm. So I have a
> suggestion. What if we can use not local variables, but local
> additional retain stacks, just like ">r" and "r>"? Let me show you
> this concept on example from recent Slava's blog-post:
>
> :: julian-day-number>date ( n -- year month day )
> #! Inverse of julian-day-number
> [let* | a [ n 32044 + ]
> b [ 4 a * 3 + 146097 /i ]
> c [ a 146097 b * 4 /i - ]
> d [ 4 c * 3 + 1461 /i ]
> e [ c 1461 d * 4 /i - ]
> m [ 5 e * 2 + 153 /i ] |
> 100 b * d + 4800 -
> m 10 /i + m 3 +
> 12 m 10 /i * -
> e 153 m * 2 + 5 /i - 1+
> ] ;
>
> This is how it looks with lisp-style locals. And here is my
> suggestion:
>
> : julian-day-number>date ( n -- year month day )
> #! Inverse of julian-day-number
> [rest n a b c d e f | >n
> n 32044 + >a
> 4 a * 3 + 146097 /i >b
> a 146097 b * 4 /i - >c
> 4 c * 3 + 1461 /i >d
> c 1461 d * 4 /i - >e
> 5 e * 2 + 153 /i >m
> 100 b * d + 4800 -
> m 10 /i + m 3 +
> 12 m 10 /i * -
> e 153 m * 2 + 5 /i - 1+
> ] ;
>
> "[rest" - is fo REtain STacks. It creates additional local stacks with
> accessors to them. Each stack ("x" for example) have three accessors.
> Traditional ">x" and "x>" with semantics of ">r" and "r>". And
> abbreviation "x" with semantics of "x> dup >x". At the end of "[rest
> ... ]" block remaining values on additional stacks are simply
> dismissed. Looks good for me.
>
> This raises major question. Is it possible to compile efficient code
> with more than one retain stack?
>
> Maxim Savchenko.
>
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