Re: First class : (was Re: Regarding the name 'pairs')
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- Subject: Re: First class : (was Re: Regarding the name 'pairs')
- From: Mark Hamburg <mark@...>
- Date: 2009年9月14日 22:58:38 -0700
On Sep 14, 2009, at 10:44 PM, Mark Hamburg wrote:
On Sep 14, 2009, at 5:26 AM, steve donovan wrote:
On Mon, Sep 14, 2009 at 2:16 PM, Luiz Henrique de Figueiredo
<lhf@tecgraf.puc-rio.br> wrote:
One important reason for not having "set:values" is that it'd be
sugar
for "function (...) return set:values(...) end" and this would imply
the creation of a hidden closure.
Yes, it did feel like an incompatible proposal.
So, is there some support for Mark Hamburg's closure sugar in
Rio ;) ?
To be fair, though I'm not sure to whom, I think someone promoted it
before I did. ;-)
But the full details of my proposal included:
1. Binds early.
2. Binds strongly. (Weak closures are a separate implementation
problem.)
3. Only generates a closure when not used at a call site though this
should be purely an optimization.
The piece of syntax I will take credit for promoting since I don't
think I'd seen it elsewhere before is:
obj:[method](...)
and in this case:
obj:[method]
Thereby allowing the method name to be an expression while at the
same time not forcing the repetition of obj in an expansion of the
colon operator.
I believe this is actually moderately easy to implement as a patch
on the current Lua implementation. (I'd have to go find my notes on
how to do so.)
In primaryexp (lparser.c), the colon operator case becomes:
case ':': { /* `:' NAME funcargs */
expdesc key;
luaX_next(ls);
/* PATCH: Add support for obj:[ exp ] syntax for calling methods. */
if (ls->t.token == '[') {
yindex(ls, &key);
}
else {
checkname(ls, &key);
}
luaK_self(fs, v, &key);
/* Compiles each expression evaluating them into a sequence of
registers. */
switch (ls->t.token) { /* PATCH: Check for a call before
going to the funcargs case, otherwise curry. */
case '(': case TK_STRING: case '{': { /* funcargs */
funcargs(ls, v);
break;
}
default: {
currymethod(ls, v);
return;
}
}
break;
}
I'm afraid I don't have an implementation for currymethod. Without
that support, the inner switch just becomes a call to funcargs(ls,v).
But to get the rest of obj:[ method ] working one also needs to revise
luaK_self in lcode.c:
void luaK_self (FuncState *fs, expdesc *e, expdesc *key) {
int func;
luaK_exp2anyreg(fs, e);
freeexp(fs, e);
func = fs->freereg;
luaK_reserveregs(fs, 2);
luaK_codeABC(fs, OP_SELF, func, e->u.s.info, luaK_exp2RK(fs, key));
freeexp(fs, key);
fs->freereg = func + 2; /* PATCH: Make sure that freeing the key
won't have just cost us a register. Why??? */
e->u.s.info = func;
e->k = VNONRELOC;
}
As the comments, suggest it would be good to have someone who knows
the register behavior in the Lua code generator better than I review
this code.
Mark