Hi Wilhelm,
> that (get ...) has a side effect! It moves the
> key that was accessed to the head of the
> symbol "tail". I assume this is a performance
> optimization to cause recently accessed
> properties to "bubble up" to the front of the
> list in case they are re-accessed soon.
Yes, exactly.
> 1. I understand why (cdr) doesn't function on
> a symbol (semantically it's not a pair) but
> I'm curious why (car) is allowed to work
> (returning the VAL)?
This is a result of the pointer structure of PicoLisp. As you may know (from
e.g. doc64/structures), a cell is
|
V
+-----+-----+
| CAR | CDR |
+-----+-----+
while a symbol is
|
V
+-----+-----+
| | VAL |
+--+--+-----+
This means, a pointer to a cell points direcly to its CAR, while a pointer to a
symbol points to its VAL. In both cases (car ...) or (val ...) are just a single
pointer derefernces (memory fetches).
> 2. Is there anyway within the REPL to inspect
> the tail structure of the symbol directly?
It is in fact possible, with some tricky pointer arithmetics:
: (put 'A 'a 1)
-> 1
: (put 'A 'b 2)
-> 2
: (val (adr (abs (adr 'A))))
-> ((2 . b) (1 . a) . 65)
> 3. Again from curiosity, I'm wondering why the
> bytes of the name are seemingly stored
> "backwards"? I'm assuming this also provides
> some performance optimization.
Correct. The first character(s) need to be accessed more prominently.
☺/ A!ex
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