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- Subject: Re: More on environments and objects
- From: Chris Marrin <chris@...>
- Date: Sat, 27 Aug 2005 20:44:15 -0700
Rici Lake wrote:
On 27-Aug-05, at 9:58 AM, Chris Marrin wrote:
Couldn't you have a rule that first tried the first way and if that
did not work (because there is not __tonumber metamethod for that
object, for instance) you would try __add? I agree that __add is
needed for things like complex numbers. I don't happen to have that
But why should you prefer __tonumber to __add? That's an entirely
problem-domain-specific preference. Put another way, if my primary
concern were complex numbers but I accepted that you also had an
application, I might say, try __add and then try __tonumber :)
That rule would work for me too! To be honest, tonumber is of no use to
me, as long as I can override all the arithmetic instructions.
__toboolean is the killer. It prevents me from saying using a bare
SFBoolean in an if test. This is easy to fix by fiddling the source to
add __boolean. But I have a dream of using a stock Lua distro!
In any event, I'm generally of the opinion that coercions should be
explicit; I'd be happier if 3+"2" where an error. I have learned the
hard way that not doing numeric conversions explicitly leads to obscure
Yes, you can never avoid obscure bugs. And I have no problem disallowing
explicit type-casting. In my system I have:
local a = 3 + SFDouble("2")
which works today.
To be honest, Lua is tantalizing close to exactly what I need. I have
already changed my source base to handle __lt, __eq and __le the way I
need them to work (allowing dissimilar types). All I need to do is add
__toboolean support. But as I said, I have this dream...
But for all intents and purposes an SFBoolean object IS a boolean
primitive. The extra features that SFBoolean provides has nothing to
do with its data type, only with how it can interact with other
properties in the system. What I really want is for Lua not to judge
me for how I want to coerce the object system :-)
That's fine. But presumably there are only two singleton members, SFTrue
and SFFalse (or am I prejudging your Boolean system? :) Relating two
enums to each other doesn't seem to me to be that painful.
If I found this acceptable:
local a = SFBoolean(true)
if a == SFTrue then...
then all would be well. But I don't. Even these two:
if a == true then...
if a:valueOf() then...
which both work after I made my "fix" to __eq, is not acceptable to me.
It has to be:
if a then...
so I will have to make the change to the VM.
This brings up what seems to be a dirty word here and many other
all over the place mention the "top languages" as Python, C++, Java,
Let me be clear that when I mention "Self" I mean "Self" :) (And I have
And for me, some of those choices are things non-programmer authors
Anyway, many of these concepts come from
Since you asked (sort of), let me list them...
to cope with corner cases. Python is even worse. Lua scopes may not be
the be-all and end-all (I would like dynamic scoping once in a blue
moon), but you can describe the entire semantics in a paragraph.
I could not agree with this more. I love Lua's static scoping rule for
its simplicity and performance. I have written and tried to cope with
destroyed performance every time. You might be interested to know that
there is an addendum for the ECMAScript spec which calls for a "compact
profile", which gets rid of "with" and all the other fiddly bits which
demand dynamic scoping, making it possible to create a statically scoped
available implementations. That is why I think there is some value in
avoid worrying about some of the issues that would make a Lua
implementation difficult. But would still give me the syntax I, for some
reason, feel I need :-)
chris marrin ,""$, "As a general rule,don't solve puzzles
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